BMJ Open€¦ · Benjawan Tawatsupa, The Australian National University Building 62 – NCEPH,...

For peer review only

Heat stress, health, and wellbeing: findings from a large national cohort of Thai adults

Journal: BMJ Open

Manuscript ID: bmjopen-2012-001396

Article Type: Research

Date Submitted by the Author: 30-Apr-2012

Complete List of Authors: Tawatsupa, Benjawan; Health Impact Assessment Division, Department of Health; National Centre for Epidemiology and Population Health, ANU College of Medicine, Biology and Environment Yiengprugsawan, Vasoonatara; The Australian National University, National Centre for Epidemiology and Population Health Kjellstrom, Tord; Centre for Global Health Research, Umeå University; The Australian National University, National Centre for Epidemiology and Population Health Seubsman, Sam-ang; Sukhothai Thammathirat Open University, School of Human Ecology Sleigh, Adrian; The Australian National University, National Centre for Epidemiology and Population Health

<b>Primary Subject Heading</b>:

Occupational and environmental medicine

Secondary Subject Heading: Epidemiology, Public health

Keywords: OCCUPATIONAL & INDUSTRIAL MEDICINE, EPIDEMIOLOGY, Epidemiology < TROPICAL MEDICINE

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Heat stress, health, and wellbeing: findings from a large

national cohort of Thai adults

Benjawan Tawatsupa1, 2,*, Vasoontara Yiengprugsawan1, Tord Kjellstrom1, 3,

Sam-ang Seubsman4, Adrian Sleigh1, and the Thai Cohort Study Team

1 National Centre for Epidemiology and Population Health, ANU College of Medicine, Biology

and Environment, the Australian National University, Canberra, Australia

2 Health Impact Assessment Division, Department of Health, Ministry of Public Health,

Nonthaburi, Thailand

3 Centre for Global Health Research, Umeå University, Umeå, Sweden

4 School of Human Ecology, Sukhothai Thammathirat Open University, Nonthaburi, Thailand

*Corresponding author:

Benjawan Tawatsupa,

The Australian National University

Building 62 – NCEPH, Mills Rd, 0200, Canberra, Australia

Email [email protected], [email protected]

Tel: +61 2 6125 5615; Fax: +61 2 6125 0740

The Thai Cohort Study Team

Thailand: Jaruwan Chokhanapitak, Chaiyun Churewong, Suttanit Hounthasarn, Suwanee

Khamman, Daoruang Pandee, Suttinan Pangsap, Tippawan Prapamontol, Janya

Puengson, Yodyiam Sangrattanakul, Sam-ang Seubsman, Boonchai Somboonsook,

Nintita Sripaiboonkij, Pathumvadee Somsamai, Duangkae Vilainerun, Wanee

Wimonwattanaphan Australia: Chris Bain, Emily Banks, Cathy Banwell, Bruce Caldwell,

Gordon Carmichael, Tarie Dellora, Jane Dixon, Sharon Friel, David Harley, Matthew

Kelly, Tord Kjellstrom, Lynette Lim, Roderick McClure, Anthony McMichael, Tanya

Mark, Adrian Sleigh, Lyndall Strazdins, Vasoontara Yiengprugsawan.

Keywords: Heat stress, health, wellbeing, Thailand Word count: 2,294 words

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Abstract

Objectives: This study aims to examine the association between hot season heat stress

interference with daily activities (sleeping, work, travel, housework, exercise) and three graded

holistic health and wellbeing outcomes (energy, emotions, life satisfaction).

Design: A cross-sectional study.

Setting: The setting is tropical and developing countries as Thailand, where high temperature

and high humidity are common, particularly during the hottest seasons.

Participants: This study is based on an ongoing national Thai Cohort Study of distance-

learning open-university adult students (N=60,569) established in 2005 to study the health-risk

transition.

Primary and secondary outcome measures: Health impacts from heat stress in our study are

categorized as physical health impacts (energy levels), mental health impacts (emotions), and

wellbeing (life satisfaction). For each health and wellbeing outcome we report Odds Ratios

(ORs) and 95% confidence intervals using multinomial logistic regression adjusting for a wide

array of potential confounders.

Results: Negative health and wellbeing outcomes (low energy level, emotional problems, and

low life satisfaction) increased with increasing frequency of heat stress interfering with daily

activities. Adjusted Odds Ratios for emotional problems were between 1·5 and 4·8 and in general

worse than energy level (between 1·31 and 2·91), and life satisfaction (between 1·10 and 2·49).

The worst health outcomes were when heat interfered with sleeping, followed by interference

with daily travel, work, housework and exercise.

Conclusions: In tropical Thailand there already are substantial heat stress impacts on health and

wellbeing. Increasing temperatures from climate change as well as the growing urban population

could significantly worsen the situation. There is a need to improve public health surveillance

and public awareness regarding the risks of heat stress in daily life.

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Article summary

• Article focus:

o To examine the association between heat stress interference with daily activities

(sleeping, work, travel, housework, exercise) during hot season and three graded

holistic health outcomes (energy, emotions, life satisfaction) in Thailand.

• Key messages:

o Negative health and wellbeing outcomes (low energy level, emotional problems,

and low life satisfaction) increased with increasing frequency of heat stress

interfering with daily activities.

o The worst health outcomes were when heat interfered with sleeping, followed

by interference with daily travel, work, housework and exercise.

o The results from this study point to the need for improving public health

surveillance and public awareness regarding the risks of heat stress in daily life in

a tropical country like Thailand.

• Strengths and limitations of this study:

o The possible limitation of self-reports, but note that questions on heat stress and

health outcomes were in different parts of the questionnaire.

o The strength of this study is its large scale with participation from a national

group of adults embedded in the socioeconomic mainstream of Thai society and

used the comprehensive questionnaire which captures a detailed assessment of

health and an array of geodemographic, environmental and social attributes.

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Introduction

Over the last decade interest has grown in the impact of global warming on human health.1

Increasing heat stress has substantial adverse effects on population mortality and morbidity.2-5

This information is from developed and temperate countries3 and leaves unanswered questions

for tropical and developing countries where high temperature and humidity are common.

Furthermore, heat stress in tropical cities is increasing due to urban heat island effects caused by

industrial development and urbanisation in developing countries.6

Heat stress can have a major influence on daily human activities. The body absorbs external heat

due to high air temperature and humidity, low air movement, and high solar radiation; as well,

some physical activities generate heat internally.7 Excess heat exposure during normal daily

activities creates a high risk of recurrent dehydration and can cause other effects on physical

health (eg, exhaustion, heat cramps, heat stroke, or death).7 Heat stress affects mood, increases

psychological distress and mental health problems,8-10 and also reduces key human psychological

performance variables.11

Other heat stress impacts may arise from increased mistakes in daily activities and accidental

injuries. As well, disturbed sleep and degraded physical performance from heat exhaustion

reduce work capacity and lead to loss of income.8,12,13 Populations at risk of heat stress are not

only the elderly but also young people and adults who are more likely to carry out heavy labour

outdoors or work indoors without air conditioning or other effective cooling systems during the

hot season.8, 12, 14

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Global warming (or “global heating” may be a better description in relation to Thailand) is now

causing increasing alarm in many tropical areas. For example, from 1951 to 2003, the monthly

mean maximum temperature in Thailand increased by 0·56˚C and the monthly mean minimum

temperature increased even more at 1·44 ˚C.15 Heat stress is already a concern in Thailand and

the observed trends indicate further increase in air temperature.16 A recent study of occupational

heat stress in Thailand by Langkulsen et al17 revealed a very serious problem (“extreme caution”

or “danger”) in an array of work settings (they tested a pottery factory, a power plant, a knife

manufacture site, a construction site and an agricultural site).

Heat stress in Thailand, its effects and pathways to exposure have been reported for two cities18,

19 and for workers.10, 20 However, there is no available information on how much heat interferes

with normal daily activities and heat stress effects on health and well-being in the general Thai

population. Here we report an investigation of heat stress effects on daily activities and on health

and wellbeing in a large national cohort of young and middle aged Thai adults.

Methods

Study population

In 2005, a baseline questionnaire was mailed out to adult students enrolled at Sukhothai

Thammathirat Open University (STOU). The questionnaire was developed by a multi-

disciplinary team in both Thailand and Australia to cover a wide range of topics for a

longitudinal study of the Thai Health-Risk Transition – transformation of the health-risk and

outcome pattern in Thailand as infectious diseases recede and chronic diseases emerge. Overall,

87,134 distance learning students aged 15 to 87 years responded from all areas of Thailand.

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Cohort participants were generally similar to the population of Thailand, especially in the 30-39

years age group, for sex ratio, income and geographical location.21

Data collected included demographic, socioeconomic and geographic characteristics, physical

and mental health status, personal wellbeing, health service use, risk behaviors, injuries, diet,

physical activity, and family background. A four-year follow-up was conducted in 2009 and the

next one is due in 2013.

This report is based on the 2009 follow-up which included questions on heat interference with

normal daily activities. The heat stress and health outcome measures (both described below)

were in different parts of the questionnaire. They could not easily be linked in the respondents

mind so answers on these issues were independent. Covariates analyzed are described with the

results and include age, sex, marital status, geographic location, work status, smoking, drinking,

and Body Mass Index.

Measures of heat stress

Questions related to heat stress were as follows: “How often did the hot period this year interfere

with the following activities?” 1) sleeping; 2) housework; 3) daily travel; 4) work; and 5)

exercise. Responses were ‘not applicable – use air conditioning’, ‘never’, ‘1-3 times per month’,

‘1-6 times per week’, and ‘every day’. For analysis, we grouped heat stress into ‘never’,

‘sometimes’ (1-3 times per month), and ‘often’ (1-6 times per week or every day).

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Measures of health and wellbeing outcomes

Health is defined by World Health Organization (WHO) as “a complete state of physical, mental,

and social wellbeing and not merely the absence of disease or infirmity”.22 Health impacts from

heat stress in our study are categorized as physical health impacts (eg, energy levels), mental

health impacts (eg, emotions), and wellbeing (eg, life satisfaction). These three outcomes were

selected because they match the holistic WHO health definition and represent fundamental health

states. Many other more specific diseases would be expected to follow adverse outcomes for

these health measures (see Discussion).

To measure the physical and mental health impacts we used two questions from the standard

Medical Outcomes Short Form Instrument (SF8) as follows: Energy: “During the past four

weeks, how much energy did you have?” Responses were ‘very much’, ‘quite a lot’, ‘some’, ‘a

little’, and ‘none’. For analysis we combined the last two categories. Emotions: “During the past

four weeks, how much have you been bothered by emotional problems (such as feeling anxious,

depressed, or irritable)?” Responses were ‘not at all’, ‘slightly’, ‘moderately’, ‘quite a lot’, and

‘extremely’. For analysis the last two categories were combined. To measure Wellbeing we used

a standardised question:23, 24 “Thinking about your own life and personal circumstances, how

satisfied are you with your life as a whole?” Scores range from 0 (‘completely dissatisfied’) to 10

(‘completely satisfied’).

Data processing and statistical analysis

Data scanning and editing involved checking the actual questionnaire response against its digital

value using Thai Scandevet, SQL and SPSS software. For analysis we used multinomial logistic

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regression reporting odds ratios (adjusted for potential confounders) based on Stata version 12.25

For all three fundamental health outcomes (energy, emotions, wellbeing), the multinomial

regression estimates the odds with which each of three increasingly severe abnormalities occurs

relative to the odds of an optimal outcome. Individuals with missing data were excluded so totals

presented vary a little according to information available.

Ethical considerations

Ethics approval was obtained from Sukhothai Thammathirat Open University Research and

Development Institute (protocol 0522/10) and the Australian National University Human

Research Ethics Committee (protocol 2009/570). Informed written consent was obtained from all

participants.

Results

Socio-demographic and health characteristics of the 60,569 cohort members followed up in 2009

are presented in Table 1. There were slightly more females (54·8%), 70% were aged less than 40

years, and 55·3% were married. Nearly 20% reported household monthly income of less than

10,000 Baht (300 $US) per month, 73·2% reported doing paid work, and 56% resided in urban

areas. Health risk behaviors - regular smoking or regular alcohol drinking -were reported by

7·7% and 13·7%, respectively. By Asian standards,26 half the cohort members were in the normal

weight range, 9·5% were underweight, 18·8% were overweight, and 22·1% were obese.

Daily activities and heat interference frequency categories are shown in Table 2. Heat

interference ‘often’ was reported (in order of frequency) by 37·5% for daily travel, 34·5% for

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work, 29·9% for housework, 27·4% for sleeping, and 25·9% for exercise. Health and wellbeing

frequency outcomes are reported in Table 3: 37·6% reported being very satisfied with their life,

around 40% reported having quite a lot or very much energy in the past 4 weeks and close to

60% reported having slight or no emotional problems in the past 4 weeks.

Daily activities show a clear trend connecting increasing heat interference with worse health and

wellbeing (Table 4). For example, cohort members who experienced heat interference ‘often’

while sleeping reported ‘extreme’ emotional problems (38·9%) much more frequently than ‘no’

emotional problems (16·4%). A similar pattern for ‘little or none’ energy levels was found for

those reporting heat interference ‘often’ while sleeping (36·1% vs 22·0%) and the same trend

was observed for life satisfaction (39·8% vs 22·2%). Daily travel and work have also shown

strong gradients connecting frequent heat interference and worse health outcomes.

The multinomial logistic regression, adjusting for a wide array of potential confounders (see

footnote for Table 5), supported the descriptive results. For all three health outcomes, when each

of the three graded adverse outcome categories is compared to the optimal outcome, the relative

odds ranged from 1·10 to 4·81. Furthermore, most ORs show a dose-response (for each health

outcome, more heat interference associates more strongly with a given grade of abnormality).

And 95% confidence intervals for all odds ratios indicated statistical significance. So heat stress

interfering with normal daily activities (sleep, housework, travel, work, exercise) associates with

adverse outcomes for all three holistic measures of health. For example, reporting heat

interference ‘often’ while sleeping was strongly associated with ‘little or none’ energy [OR =

2·23, 95% CI 2·02-2·46], ‘extreme’ emotional problems [OR = 4·81, 95% CI 4·32-5·36] and

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‘low’ life satisfaction [OR = 2·49, 95% CI 2·28-2·71]. At work, reporting heat interference

‘often’ was associated with ‘little or none’ energy [OR = 2·45, 95% CI 2·22-2·71] and ‘extreme’

emotional problems [OR = 3·64, 95% CI 3·31-4·00]. Similar results were found during daily

travel and doing housework. A statistically significant association was also found for heat

inference during exercise but the magnitude of the effect was lower than for other activities.

Discussion

Our study shows that climate-related heat stress in tropical Thailand adversely affects self-

reported health and wellbeing if the heat interferes with daily activities such as sleep, housework,

travel, work, and exercise. The large study group included young and middle-age Thai adults,

mostly doing paid work, with over half residing in urban areas. These people are active and over

20% reported often experiencing heat interference for daily activities during the hot season.

Daily travel and work were sources of heat stress more often than other activities, probably

because they involve time spent in traffic or outdoors during hot periods. Other activities such as

housework have less heat stress than daily travel and work, perhaps because these activities are

home-based where air-conditioning or other ventilation is available.

We found negative health and wellbeing outcomes (low life satisfaction, low energy level, and

emotional problems) increased with higher frequency of heat stress while performing daily

activities. Odds Ratios of heat stress across all daily activities for emotional problems are

between 1·55 and 4·81 and in general worse than energy level effects (between 1·31 and 2·91)

and life satisfaction effects (between 1·10 and 2·49). The worst health outcomes were for heat

stress while sleeping followed by daily travel, work, housework and exercise.

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Our studied outcomes were holistic fundamental measures of health. We can expect that those

who had abnormal findings would also (already or eventually) manifest other more specific

chronic diseases such as depression, obesity, hypertension, and kidney disease. If so, the eventual

burden of heat-related disease will be higher than currently recognized.27-29

We acknowledge the possible limitation of self-reports, but note that questions on heat stress and

health outcomes were in different parts of the questionnaire. However, the findings show a

strong and highly consistent trend especially for adverse health effects of frequent heat

interference during sleep, daily travel, and work. The strength of this study is its large scale with

participation from a national group of adults embedded in the socioeconomic mainstream of Thai

society. Other strengths include the comprehensive questionnaire which captures a detailed

assessment of health and an array of geodemographic, environmental and social attributes. Also,

the cohort has been set up for future longitudinal analysis which will provide better insight into

causal pathways between heat stress and subsequent health outcomes in the long run.

Our findings add to some previous reports on working in hot environments which found that heat

stress significantly reduced people’s motivation to do their work. Lan et al30 assessed office

workers’ perceptions of thermal environment, emotions, well-being, and motivation to work, and

found that participants had lower motivation to work and experienced more negative moods in

hot environments. Anderson found that the prolonged, continuous repetitive actions required to

maintain performance at work and achieve target goals (such as getting a job finished) can lead

to hypertension.31 And when more effort was required to complete a task in hot conditions loss

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of motivation was experienced leading to lower productivity and increased injury risk. The

impact of heat stress on psychological performance variables11 is a likely factor in these work

related impacts of heat. Psychological effects of heat stress have been noted in other settings as

well. Nitschke et al32 reported a positive association between high ambient temperature and

hospital admissions for mental and behavioral disorders in Adelaide, Australia. Specific illnesses

for which admissions increased included anxiety, symptomatic mood disorders, and

psychological development disorders among elderly people when temperature exceeded

26·7°C.33 Moreover, excessive heat stress exposure may also increase violence.31-34 Increasing

heat stress had been associated with higher rates of aggressive behavior,35 and higher violent

suicide rates.36 In a meta-analysis, Bouchama et al37 concluded that pre-existing mental health

problems tripled the risk of all-cause mortality during a heat wave. A related issue is the physical

and psychological exhaustion caused by extreme heat stress.7

Thai populations are at high risk of heat stress during daily activities. Also, in Thailand an

anticipated increase in temperature from climate change plus the growing urban population could

significantly increase heat impacts on health and wellbeing. There is a need for improvements in

public health surveillance and public awareness regarding the risks of heat stress which hitherto

have been considered unremarkable in such a tropical environment.

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Tables

Table 1 Socio-demographic and health characteristics of Thai cohort members in 2009

Cohort characteristics N = 60,569 %

Demographic characteristics

Sex Male 45.3

Female 54.8

Age (year) ≤ 29 27.4

30-39 42.6

40+ 30.0

Marital status Married 55.3

Never married 37.9

Separated, divorced, widowed 6.8

Socio-geographic characteristics

Monthly income (Baht)* <10,000 18.8

10,000-19,999 22.4

20,000-30,000 35.7

>30,000 23.1

Work status Doing paid work 73.2

Unpaid family workers 7.3

Seeking work 2.2

Others 17.3

Residence Rural residence 44.0

Urban residence 56.0

Health risk behaviors

Regular smokers 7.7

Regular alcohol drinkers 13.7

Body Mass Index (kg/m2)

Underweight (<18.5) 9.5

Normal (18.5-22.9) 49.5

Overweight at risk (23-24.9) 18.8

Obese (25+) 22.1

*Household monthly income in 2009 (US$ = 35 Baht)

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Table 2 Daily activities and heat interference category among Thai cohort members in 2009

Daily activities

N = 60,569

Heat interference (%)

Not applicable* Never Sometimes Often

Sleeping 15.7 24.3 32.5 27.4

Housework 1.3 37.1 31.7 29.9

Daily travel 3.0 33.7 25.8 37.5

Work 14.0 30.3 21.2 34.5

Exercise 0.8 43.1 30.1 25.9

*Use air conditioner

Table 3 Health and wellbeing outcomes among Thai cohort members in 2009

Outcomes

N = 60,569

%

Overall life satisfaction (score ranged from 0 to 10)

9-10 very satisfied (highest) 37.6

8 (high) 28.8

6-7 (medium) 21.7

0-5 not very satisfied (low) 12.0

Energy level in the past 4 weeks

very much 14.4

quite a lot 25.8

some 48.4

a little or none 11.3

Emotional problems in the past 4 weeks

not at all 14.9

slightly 44.0

moderately 32.0

quite a lot/extremely 9.1

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Table 4 Frequency of heat interference with daily activities by health & wellbeing outcomes among cohort members

Daily activities and

heat interference

category

Health and wellbeing outcomes N=60,569

% Life satisfaction

score ranged from 0 to 10

% Energy level

in the past 4 weeks

% Emotional problems

in the past 4 weeks

9-10

highest

8

high

6-7

medium

0-5

low

very much quite a lot some

little/ none not at all slightly

moderate

extreme

Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)

never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6

sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3

often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9

Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)

never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7

sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4

often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9

Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)

never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2

sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4

often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0

Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)

never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6

sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9

often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7

Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)

never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2

sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9

often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2

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Table 5 Association between heat interference with daily activities and health & wellbeing outcomes among cohort members

Heat

interference

category

N=60,569

Adjusted* Odds Ratios and 95% Confidence Interval

Life satisfaction (score 0-10)** Energy level in the past 4 weeks Emotional problems in the past 4 weeks

high

vs

highest

medium

vs

highest

low

vs

highest

quite a lot

vs

very much

some

vs

very much

little/none

vs

very much

slightly

vs

not at all

moderate

vs

not at all

extreme

vs

not at all

Sleep

never ref ref ref ref ref ref ref ref ref

sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]

often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]

Housework


sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]

often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]

Daily travel


sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]

often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]

Work


sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]

often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]

Exercise


sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]

often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]

*Multivariate regression adjusting for potential confounders: age, sex, marital status, work status, household income, urban-rural residence, exercise, housework, hours of

sleep, body mass index, smoking , and drinking

**Life satisfaction scores: highest = 9-10, high = 8, medium = 6-7, low = 0-5

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Tawatsupa Page 17

Acknowledgments

This study was supported by the International Collaborative Research Grants Scheme with

joint grants from the Wellcome Trust UK (GR071587MA) and the Australian National Health

and Medical Research Council (NHMRC 268055), and as a global health grant from the

NHMRC (585426). These funding bodies play no role in the preparation or submission of this

manuscript. We thank the staff at Sukhothai Thammathirat Open University (STOU) who

assisted with student contact, and the STOU students who are participating in the cohort

study. We also thank Dr Bandit Thinkamrop and his team from Khon Kaen University for

guiding us successfully through the complex data processing.

Competing interests

We declare that we have non-financial competing interests.

Contributor statement

The corresponding author had full access to all data used in the study and had final

responsibility for the decision to submit for publication. BT and VY conceptualized the

analysis for this paper with contributions from all authors. BT and VY wrote the first draft.

BT did the literature search and VY did statistical analyses. TK had the initial idea for the

heat stress study. SS and AS conceived and executed the Thai Cohort Study and assisted with

the writing and interpretation. All authors contributed to and approved the final version.

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29. Kjellstrom T, Butler AJ, Lucas RM, et al. Public health impact of global heating due to

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32. Nitschke M, Tucker GR, Bi P. Morbidity and mortality during heatwaves in metropolitan

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34. Anderson C, Anderson K, Dorr N, et al. Temperature and aggression Adv Experimental

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36. Maes M, De Meyer F, Thompson P, et al. Synchronized annual rhythms in violent suicide

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STROBE 2007 (v4) Statement—Checklist of items that should be included in reports of cross-sectional studies

Section/Topic Item

# Recommendation Reported on page #

Title and abstract 1 (a) Indicate the study’s design with a commonly used term in the title or the abstract 2

(b) Provide in the abstract an informative and balanced summary of what was done and

what was found

2

Introduction

Background/rationale 2 Explain the scientific background and rationale for the investigation being reported 4

Objectives 3 State specific objectives, including any prespecified hypotheses 5

Methods

Study design 4 Present key elements of study design early in the paper 7

Setting 5 Describe the setting, locations, and relevant dates, including periods of recruitment,

exposure, follow-up, and data collection

5

Participants

6

(a) Give the eligibility criteria, and the sources and methods of selection of participants 5

Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and effect

modifiers. Give diagnostic criteria, if applicable

6

Data sources/

measurement

8* For each variable of interest, give sources of data and details of methods of assessment

(measurement). Describe comparability of assessment methods if there is more than

one group

6

(Our heat exposed group include respondents who

reported heat interfere their daily activities at 1-6 times

per week or every day. An unexposed group include

those who reported never experienced heat or 1-3 times

per month)

Bias 9 Describe any efforts to address potential sources of bias 6

Study size 10 Explain how the study size was arrived at 8

Quantitative variables 11 Explain how quantitative variables were handled in the analyses. If applicable, describe

which groupings were chosen and why

7

Statistical methods 12 (a) Describe all statistical methods, including those used to control for confounding 7

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(b) Describe any methods used to examine subgroups and interactions 7

(c) Explain how missing data were addressed 8

(d) If applicable, describe analytical methods taking account of sampling strategy -

(e) Describe any sensitivity analyses -

Results

Participants 13* (a) Report numbers of individuals at each stage of study—eg numbers potentially

eligible, examined for eligibility, confirmed eligible, included in the study, completing

follow-up, and analysed

8

(b) Give reasons for non-participation at each stage -

(c) Consider use of a flow diagram -

Descriptive data 14* (a) Give characteristics of study participants (eg demographic, clinical, social) and

information on exposures and potential confounders

8

(b) Indicate number of participants with missing data for each variable of interest -

Outcome data 15* Report numbers of outcome events or summary measures 9

Main results 16 (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and

their precision (eg, 95% confidence interval). Make clear which confounders were

adjusted for and why they were included

9

(b) Report category boundaries when continuous variables were categorized -

(c) If relevant, consider translating estimates of relative risk into absolute risk for a

meaningful time period

-

Other analyses 17 Report other analyses done—eg analyses of subgroups and interactions, and sensitivity

analyses

10

Discussion

Key results 18 Summarise key results with reference to study objectives 10

Limitations 19 Discuss limitations of the study, taking into account sources of potential bias or

imprecision. Discuss both direction and magnitude of any potential bias

11

Interpretation 20 Give a cautious overall interpretation of results considering objectives, limitations,

multiplicity of analyses, results from similar studies, and other relevant evidence

11

Generalisability 21 Discuss the generalisability (external validity) of the study results 11

Other information

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Funding 22 Give the source of funding and the role of the funders for the present study and, if

applicable, for the original study on which the present article is based

17

*Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies.

Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE

checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at http://www.plosmedicine.org/, Annals of Internal Medicine at

http://www.annals.org/, and Epidemiology at http://www.epidem.com/). Information on the STROBE Initiative is available at www.strobe-statement.org.

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Journal: BMJ Open

Manuscript ID: bmjopen-2012-001396.R1


Date Submitted by the Author: 20-Jul-2012









jopen.bmj.com

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1 National Centre for Epidemiology and Population Health, ANU College of Medicine,

Biology and Environment, the Australian National University, Canberra, Australia






Benjawan Tawatsupa,




Tel: +61 2 6125 5615; Fax: +61 2 6125 0740


Thailand: Jaruwan Chokhanapitak, Chaiyun Churewong, Suttanit Hounthasarn,

Suwanee Khamman, Daoruang Pandee, Suttinan Pangsap, Tippawan Prapamontol,

Janya Puengson, Yodyiam Sangrattanakul, Sam-ang Seubsman, Boonchai

Somboonsook, Nintita Sripaiboonkij, Pathumvadee Somsamai, Duangkae Vilainerun,

Wanee Wimonwattanaphan Australia: Chris Bain, Emily Banks, Cathy Banwell,

Bruce Caldwell, Gordon Carmichael, Tarie Dellora, Jane Dixon, Sharon Friel, David

Harley, Matthew Kelly, Tord Kjellstrom, Lynette Lim, Roderick McClure, Anthony

McMichael, Tanya Mark, Adrian Sleigh, Lyndall Strazdins, Vasoontara

Yiengprugsawan.


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Abstract

Objectives: This study aims to examine the association between self-reported heat stress

interference with daily activities (sleeping, work, travel, housework, exercise) and three

graded holistic health and wellbeing outcomes (energy, emotions, life satisfaction).





learning open-university adult students (N=60,569) established in 2005 to study the health-

risk transition.

Primary and secondary outcome measures: Health impacts from heat stress in our study

are categorized as physical health impacts (energy levels), mental health impacts (emotions),

and wellbeing (life satisfaction). For each health and wellbeing outcome we report Odds

Ratios (ORs) and 95% confidence intervals using multinomial logistic regression adjusting

for a wide array of potential confounders.

Results: Negative health and wellbeing outcomes (low energy level, emotional problems,

and low life satisfaction) increased with increasing frequency of heat stress interfering with

daily activities. Adjusted Odds Ratios for emotional problems were between 1·5 and 4·8 and

in general worse than energy level (between 1·31 and 2·91), and life satisfaction (between

1·10 and 2·49). The worst health outcomes were when heat interfered with sleeping, followed


Conclusions: In tropical Thailand there already are substantial heat stress impacts on health

and wellbeing. Increasing temperatures from climate change plus the ageing and urbanisation

of the population could significantly worsen the situation. There is a need to improve public

health surveillance and public awareness regarding the risks of heat stress in daily life.

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Article summary

• Article focus:

o To examine the association between self-reported heat stress interference with

daily activities (sleeping, work, travel, housework, exercise) during hot season

and three graded holistic health outcomes (energy, emotions, life satisfaction)

in Thailand.

• Key messages:

o Negative health and wellbeing outcomes (low energy level, emotional

problems, and low life satisfaction) increased with increasing frequency of heat

stress interfering with daily activities.




surveillance and public awareness regarding the risks of heat stress in daily life

in a tropical country like Thailand.


o The possible limitation of self-reports, but note that questions on heat stress

and health outcomes were in different parts of the questionnaire.


group of adults embedded in the socioeconomic mainstream of Thai society

and used the comprehensive questionnaire which captures a detailed

assessment of health and an array of geodemographic, environmental and

social attributes.

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Introduction

Over the last decade interest has grown in the impact of global warming on human health.(1)

Increasing heat stress has substantial adverse effects on population mortality and

morbidity.(2-5) This information is from developed and temperate countries(3) and leaves

unanswered questions for tropical and developing countries where high temperature and

humidity are common. Furthermore, heat stress in tropical cities is increasing due to urban

heat island effects caused by industrial development and urbanisation in developing

countries.(6)

Heat stress can have a major influence on daily human activities. The body absorbs external

heat due to high air temperature and humidity, low air movement, and high solar radiation; as

well, some physical activities generate heat internally.(7) Excess heat exposure during normal

daily activities creates a high risk of recurrent dehydration and can cause other effects on

physical health (eg, exhaustion, heat cramps, heat stroke, or death).(7) Heat stress affects

mood, increases psychological distress and mental health problems,(8-10) and also reduces

key human psychological performance variables.(11)



reduce work capacity and lead to loss of income.(8, 12-13) Populations at risk of heat stress

are not only the elderly but also young people and adults who are more likely to carry out

heavy labour outdoors or work indoors without air conditioning or other effective cooling

systems during the hot season.(8, 12, 14)

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In tropical Thailand, hot and humid conditions are common, especially in the hot season

(March - June). The monthly maximum, mean and minimum temperatures averaged from

1999 to 2008 were around 33°C, 27°C, and 22°C respectively with the averaged relative

humidity at 75%. The monthly maximum temperatures averaged during ten years varied little

by region (32-33°C) and were highest in the North region during April (40°C) and lowest in

the same region during December (24°C).(Tawatsupa et al, unpublished data, 2012)

Global warming (or “global heating” may be a better description in relation to Thailand) is

now causing increasing alarm in many tropical areas. For example, from 1951 to 2003, the

monthly mean maximum temperature in Thailand increased by 0·56˚C and the monthly mean

minimum temperature increased even more at 1·44 ˚C.(15) Heat stress is already a concern in

Thailand and the observed trends indicate further increase in air temperature.(16) A recent

study of occupational heat stress in Thailand by Langkulsen et al(17) revealed a very serious

problem (“extreme caution” or “danger”) in an array of work settings (they tested a pottery

factory, a power plant, a knife manufacture site, a construction site and an agricultural site).

Heat stress in Thailand, its effects and pathways to exposure have been reported for two cities

(18-19) and for workers.(10, 20) However, there is no available information on how much

heat interferes with normal daily activities and heat stress effects on health and well-being in

the general Thai population. Here we report an investigation of heat stress effects on daily

activities and on health and wellbeing in a large national cohort of young and middle aged

Thai adults.

Methods

Study population

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outcome pattern in Thailand as infectious diseases recede and chronic diseases emerge.

Overall, 87,134 distance learning students aged 15 to 87 years responded from all areas of

Thailand. Cohort participants were generally similar to the population of Thailand, especially

in the 30-39 years age group, for sex ratio, income and geographical location.(21)



physical activity, and family background. A four-year follow-up was conducted in 2009 and

the next one is due in 2013.




mind so answers on these issues were independent. Covariates analyzed are described with

the results and include age, sex, marital status, geographic location, work status, smoking,

drinking, and Body Mass Index.


Questions related to heat stress were as follows: “How often did the hot period this year

interfere with the following activities?” 1) sleeping; 2) housework; 3) daily travel; 4) work;

and 5) exercise. Responses were ‘not applicable – use air conditioning’, ‘never’, ‘1-3 times

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per month’, ‘1-6 times per week’, and ‘every day’. In this study, heat interference means heat

stress causing an uncomfortable feeling when doing those daily activities. For analysis, we

grouped self-reported heat stress into ‘never’, ‘sometimes’ (1-3 times per month), and ‘often’

(1-6 times per week or every day).


Health is defined by World Health Organization (WHO) as “a complete state of physical,

mental, and social wellbeing and not merely the absence of disease or infirmity”.(22) Health

impacts from heat stress in our study are categorized as physical health impacts (eg, energy

levels), mental health impacts (eg, emotions), and wellbeing (eg, life satisfaction). These three

outcomes were selected because they match the holistic WHO health definition and represent

fundamental health states. Many other more specific diseases would be expected to follow

adverse outcomes for these health measures (see Discussion).



weeks, how much energy did you have?” Responses were ‘very much’, ‘quite a lot’, ‘some’,

‘a little’, and ‘none’. For analysis we combined the last two categories. Emotions: “During the

past four weeks, how much have you been bothered by emotional problems (such as feeling

anxious, depressed, or irritable)?” Responses were ‘not at all’, ‘slightly’, ‘moderately’, ‘quite

a lot’, and ‘extremely’. For analysis the last two categories were combined. To measure

Wellbeing we used a standardised question:(23-24) “Thinking about your own life and

personal circumstances, how satisfied are you with your life as a whole?” Scores range from 0

(‘completely dissatisfied’) to 10 (‘completely satisfied’).

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Data scanning and editing involved checking the actual questionnaire response against its

digital value using Thai Scandevet, SQL and SPSS software. For analysis we used

multinomial logistic regression reporting odds ratios (adjusted for potential confounders)

based on Stata version 12.(25) For all three fundamental health outcomes (energy, emotions,

wellbeing), the multinomial regression estimates the odds with which each of three

increasingly severe abnormalities occurs relative to the odds of an optimal outcome.

Individuals with missing data were excluded so totals presented vary a little according to

information available.




Research Ethics Committee (protocol 2009/570). Informed written consent was obtained from

all participants.

Results

We first compared the 2005–2009 cohort to those who dropped out in 2009 (data not shown).

The two groups were similar for age, sex ratio, employment, income, and health outcomes

studied here (energy levels, emotional problems, life satisfaction). Socio-demographic and

health characteristics of the 60,569 cohort members followed up in 2009 are presented in

Table 1. There were slightly more females (54·8%), 70% were aged less than 40 years, and

55·3% were married. Nearly 20% reported household monthly income of less than 10,000

Baht (300 $US) per month, 73·2% reported doing paid work, and 56% resided in urban areas.

Health risk behaviors - regular smoking or regular alcohol drinking -were reported by 7·7%

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and 13·7%, respectively. By Asian standards,(26) half the cohort members were in the normal


We noted that prevalence of ‘often’ heat interference for each daily activity are not much

different in different regions of Thailand (33-42% for daily travel, 29-38% for work, 26-32%

for housework, 23-29% for sleeping, and 22-28% for exercise). Daily activities and heat

interference frequency categories are summarized in Table 2. Heat interference ‘often’ was

reported (in order of frequency) by 37·5% for daily travel, 34·5% for work, 29·9% for

housework, 27·4% for sleeping, and 25·9% for exercise. Health and wellbeing frequency

outcomes are reported in Table 3: 37·6% reported being very satisfied with their life, around

15% reported having very much energy in the past 4 weeks and close to 11% reported no

emotional problems in the past 4 weeks.

Daily activities show a clear trend connecting increasing heat interference with worse health

and wellbeing (Table 4). For example, cohort members who experienced heat interference

‘often’ while sleeping reported ‘extreme’ emotional problems (38·9%) much more frequently

than ‘no’ emotional problems (16·4%). A similar pattern for ‘little or none’ energy levels was

found for those reporting heat interference ‘often’ while sleeping (36·1% vs 22·0%) and the

same trend was observed for life satisfaction (39·8% vs 22·2%). Daily travel and work have

also shown strong gradients connecting frequent heat interference and worse health outcomes.


footnote for Table 5), supported the descriptive results. For all three health outcomes, when

each of the three graded adverse outcome categories is compared to the optimal outcome, the

relative odds ranged from 1·10 to 4·81. Furthermore, most ORs show a dose-response (for

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each health outcome, more heat interference associates more strongly with a given grade of

abnormality). And 95% confidence intervals for all odds ratios indicated statistical

significance. So heat stress interfering with normal daily activities (sleep, housework, travel,

work, exercise) associates with adverse outcomes for all three holistic measures of health. For

example, reporting heat interference ‘often’ while sleeping was strongly associated with ‘little

or none’ energy [OR = 2·23, 95% CI 2·02-2·46], ‘extreme’ emotional problems [OR = 4·81,

95% CI 4·32-5·36] and ‘low’ life satisfaction [OR = 2·49, 95% CI 2·28-2·71]. At work,

reporting heat interference ‘often’ was associated with ‘little or none’ energy [OR = 2·45,

95% CI 2·22-2·71] and ‘extreme’ emotional problems [OR = 3·64, 95% CI 3·31-4·00]. Similar

results were found during daily travel and doing housework. A statistically significant

association was also found for heat inference during exercise but the magnitude of the effect

was lower than for other activities.

Discussion

Our study shows that climate-related heat stress in tropical Thailand adversely affects self-

reported health and wellbeing if the heat interferes with daily activities such as sleep,

housework, travel, work, and exercise. The large study group included young and middle-age

Thai adults, mostly doing paid work, with over half residing in urban areas. These people are

active and over 20% reported often experiencing heat interference for daily activities during

the hot season. Daily travel and work were sources of heat stress more often than other

activities, probably because they involve time spent in traffic or outdoors during hot periods.

Other activities such as housework have less heat stress than daily travel and work, perhaps

because these activities are home-based where air-conditioning or other ventilation is

available.

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We found negative health and wellbeing outcomes (low life satisfaction, low energy level,

and emotional problems) increased with higher frequency of heat stress while performing

daily activities. Odds Ratios of heat stress across all daily activities for emotional

problems are between 1·55 and 4·81 and in general worse than energy level effects (between

1·31 and 2·91) and life satisfaction effects (between 1·10 and 2·49). The worst health

outcomes were for heat stress while sleeping followed by daily travel, work, housework and

exercise.

Elsewhere we have completed detailed analyses of associations between heat stress and self-

reported health outcomes in the cohort using the questions from SF8 (10). Our studied

outcomes in this report were holistic fundamental measures of health. We can expect that

those who had abnormal findings would also (already or eventually) manifest other more

specific chronic diseases such as depression, obesity, hypertension, and kidney disease. If so,

the eventual burden of heat-related disease will be higher than currently recognized.(27-29)

We acknowledge the possible limitation of self-reports, but note that questions on heat stress

and health outcomes were in different parts of the questionnaire. However, the findings show

a strong and highly consistent trend especially for adverse health effects of frequent heat

interference during sleep, daily travel, and work. The strength of this study is its large scale

with participation from a national group of adults embedded in the socioeconomic mainstream

of Thai society. Other strengths include the comprehensive questionnaire which captures a

detailed assessment of health and an array of geodemographic, environmental and social

attributes. Also, the cohort has been set up for future longitudinal analysis which will provide

better insight into causal pathways between heat stress and subsequent health outcomes in the

long run.

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Our findings add to some previous reports on working in hot environments which found that

heat stress significantly reduced people’s motivation to do their work. Lan et al (30) assessed

office workers’ perceptions of thermal environment, emotions, well-being, and motivation to

work, and found that participants had lower motivation to work and experienced more

negative moods in hot environments. Anderson found that the prolonged, continuous

repetitive actions required to maintain performance at work and achieve target goals (such as

getting a job finished) can lead to hypertension.(31) And when more effort was required to

complete a task in hot conditions loss of motivation was experienced leading to lower

productivity and increased injury risk. The impact of heat stress on psychological

performance variables (11) is a likely factor in these work related impacts of heat.

Psychological effects of heat stress have been noted in other settings as well. Nitschke et al

(32) reported a positive association between high ambient temperature and hospital

admissions for mental and behavioral disorders in Adelaide, Australia. Specific illnesses for

which admissions increased included anxiety, symptomatic mood disorders, and


26·7°C.(33) Moreover, excessive heat stress exposure may also increase violence.(31-34)

Increasing heat stress had been associated with higher rates of aggressive behavior,(35) and

higher violent suicide rates.(36) In a meta-analysis, Bouchama et al (37) concluded that pre-

existing mental health problems tripled the risk of all-cause mortality during a heat wave. A

related issue is the physical and psychological exhaustion caused by extreme heat stress. (7)

In our study, we found that heat stress in Thailand is not only a problem at work but also heat

stress interferes with other daily activities including sleeping, daily travel, housework and

exercise. The results of our study complement other Thai research about adverse effects of

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heat. One recent report shows that heat stress in Thailand is a very serious problem in a wide

variety of work settings (17). McMichael et al (18) and Guo et al (38) found a temperature–

mortality association and Pudpong et al (19) found heat related excess hospital admissions.

Worker studies in Thailand related occupational heat stress, kidney disease and psychological

distress.(10, 20)

We conclude that Thai populations are at high risk of heat stress during daily activities. Also,

in Thailand an anticipated increase in temperature from climate change plus the ageing and

urbanisation of the population could significantly increase heat impacts on health and

wellbeing. There is a need for improvements in public health surveillance and public

awareness regarding the risks of heat stress which hitherto have been considered

unremarkable in such a tropical environment.

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Tables




Sex Male 45.3

Female 54.8

Age (year) ≤ 29 27.4

30-39 42.6

40+ 30.0


Never married 37.9



Monthly income (Baht)* ≤10,000 18.8

10,001-20,000 22.4

20,001-30,000 35.7

>30,000 23.1



Seeking work 2.2

Others 17.3




Regular smokers 7.7




Normal (18.5-22.9) 49.5


Obese (25+) 22.1


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Daily activities

N = 60,569



Sleeping 15.7 24.3 32.5 27.4

Housework 1.3 37.1 31.7 29.9

Daily travel 3.0 33.7 25.8 37.5

Work 14.0 30.3 21.2 34.5

Exercise 0.8 43.1 30.1 25.9



Outcomes

N = 60,569

%



8 (high) 28.8

6-7 (medium) 21.7



very much 14.9

quite a lot 44.0

some 32.0



not at all 11.3

slightly 48.4

moderately 25.8


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heat interference

category


% Life satisfaction


% Energy level

in the past 4 weeks


in the past 4 weeks

9-10

highest

8

high

6-7

medium

0-5

low



moderate

extreme

Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)

never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6

sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3

often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9

Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)

never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7

sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4

often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9

Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)

never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2

sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4

often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0

Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)

never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6

sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9

often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7

Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)

never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2

sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9

often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2

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Heat

interference

category

N=60,569



high

vs

highest

medium

vs

highest

low

vs

highest

quite a lot

vs

very much

some

vs

very much

little/none

vs

very much

slightly

vs

not at all

moderate

vs

not at all

extreme

vs

not at all

Sleep


sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]

often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]

Housework


sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]

often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]

Daily travel


sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]

often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]

Work


sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]

often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]

Exercise


sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]

often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]




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Acknowledgments









Competing interests









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37. Bouchama A, Dehbi M, Mohamed G, Matthies F, Shoukri M, Menne B. Prognostic factors in heat wave-related deaths: A meta-analysis. Arch Intern Med. 2007;167(20):2170-6.

38. Guo Y, Punnasiri K, Tong S. Effects of temperature on mortality in Chiang Mai city, Thailand: a time series study. Environ Health. 2012;11(1):36.

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Response to Decision Letter to BMJ Open

Date: 20/07/12

Manuscript ID: bmjopen-2012-001396

Title: "Heat stress, health, and wellbeing: findings from a large national cohort of Thai adults"

Dear Managing Editor, BMJ Open

I have completed the revised manuscript "Heat stress, health, and wellbeing: findings from a large

national cohort of Thai adults" (Manuscript ID: bmjopen-2012-001396)

I would like to resubmit this revised version of the manuscript. The changes in the manuscript were

indicated by using red font color. We have also responded to the reviewers’ comments and

suggestions in this document, reproducing in indented paragraphs the red font manuscript

revisions and explaining in blue font how each point is addressed and why we responded as we

did.

Response to Reviewer comments

1. Reviewer: Prof. Yuk Yee Yan (Department of Geography, Hong Kong Baptist University

Kowloon Tong, Hong Kong)

1) The study examined the impact of heat stress in the hot season in Thailand. When is the hot

season in Thailand? What are the maximum, mean, minimum temperatures and relative humidity?

Is there any spatial variations? I would suggest the authors to have a brief description of the

climate in Thailand.

We have added information of climate in Thailand in the Introduction section (4th paragraph)

in Page 5.

“…In tropical Thailand, hot and humid conditions are common, especially in the hot season



humidity at 75%. The monthly maximum temperatures averaged during ten years varied

little by region (32-33°C) and were highest in the North region during April (40°C) and

lowest in the same region during December (24°C) (Tawatsupa et al., 2012a)..”

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2) The subjects of the study came from all areas of Thailand. Were the subjects evenly distributed

geographically (i.e. were the number of subjects from various parts of Thailand the same)? If there

is geographical variations in climate, responses of the subjects may also be different. I would like

the authors to address these questions.

Regarding our response to comments No. 1, the monthly maximum temperature averaged

during 1999 to 2008 varied little by geographical region (32-33°C). We are also aware of the

responses to heat stress of subjects in different area of Thailand. Here (for this response to item 2)

we did additional analysis to show the number of study population, number of respondents and %

prevalence of often heat interference daily activities by region of Thailand (Table A, below – not for

inclusion in the paper). We also added a sentence in the Result section (2nd paragraph) in page 9;

“…We noted that the prevalence of ‘often’ heat interference for each daily activity are not

much different in different regions (33-42% for daily travel, 29-38% for work, 26-32% for

housework, 23-29% for sleeping, and 22-28% for exercise). Daily activities and heat

interference frequency categories are summarized in Table 2.…”

Table A. Study population, and % prevalence of ‘often’ heat interference daily activities by

region of Thailand.

Daily activities Bangkok Central North Northeast South Total

Total N 10,310 15,349 11,329 15,912 7,668 60,569 Often heat interference

Sleeping N 2,638 4,243 3,267 4,462 1,729 16,339 % 26.0 28.1 29.3 28.6 23.0 27.4

Housework N 2,903 4,634 3,525 4,787 1,922 17,771 % 28.7 30.8 31.7 30.7 25.6 29.9

Daily travel N 4,283 5,886 3,972 5,635 2,515 22,291 % 42.3 39.1 35.7 36.2 33.5 37.5

Work N 2,970 5,080 4,132 5,891 2,408 20,481 % 29.4 33.7 37.1 37.8 32.0 34.5

Exercise N 2,371 3,800 3,105 4,427 1,690 15,393 % 23.5 25.3 27.9 28.4 22.5 25.9

.------------------------------------------

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2. Reviewer: Prof. S. Tong (School of Public Health and Social Work, Institute of Health and

Biomedical Innovation, Queensland University of Technology, AUSTRALIA)

1) About one third of the participants were lost to follow-up in 2009 and what is the potential for

loss to follow-up bias? A table should be provided to compare the characteristics of the participants

and those who were lost to follow-up in 2009.

To respond to this item 1, we have prepared a table comparing overall socio-demographic

and health characteristics of the 60,569 cohort members followed up in 2009 and those 26,578

participants who lost to follow-up (Table B). It is not necessary to include this table and we have

started the Results (in Page 8) with the following inserted sentence.

“…We first compared the 2005–2009 cohort to those who dropped out in 2009 (data not

shown). The two groups were similar for age, sex ratio, employment, income, and health

outcomes studied here (energy levels, emotional problems, life satisfaction)…”

Table B. Socio-demographic and health characteristics in 2005 of Thai cohort member in the follow-up group and who loss in the 2009

Cohort characteristics in 2005 Cohort members in 2005&2009

Participants only in 2005

Total

Total N 60,569 26,578 87,174

Sex

Male 45.3 45.5 45.3

Female 54.7 54.5 54.7

Personal monthly incomes

<= 3000 9.5 14.6 11.0

3001-7000 28.7 36.1 30.9

7001-10000 23.4 23.0 23.3

10001-20000 26.5 18.8 24.2

20001-30000 7.2 4.1 6.3

>30000 4.7 3.4 4.3

Work for income

Yes 88.4 82.4 86.5

No 11.7 17.7 13.5

Energy levels in the past 4 weeks

Very much 17.4 17.5 17.4

Quite a lot 42.7 42.0 42.5

Some 30.0 29.8 30.0

A little or none 9.9 10.8 10.2 Emotional problems in the past 4 weeks

Not at all 10.9 8.9 10.3

Slightly 53.0 49.2 51.9

Moderately 21.9 24.3 22.6

Quite a lot / extremely 14.2 17.6 15.2

Overall life satisfaction

9-10 very satisfied (highest) 31.7 29.3 31.0

8 (high) 28.7 26.8 28.1

6-7 (medium) 25.9 26.5 26.1

0-5 not very satisfied (low) 13.7 17.4 14.9

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2) More details are needed for the Methods section. For instance, it is unclear how valid the

questions used in the survey instrument are. They stated that “Questions related to heat stress

were as follows: “How often did the hot period this year interfere with the following activities? 1)

sleeping; 2) housework…” However, there is no description about how they defined the

interference. It could lead to over- or/and under-estimates of heat impacts if the definition is

unclear.

We added a sentence describing the definition of heat interference (in Methods section,

under Measures of heat stress, page 7). Also, we now have a validation study for heat stress

question by calling back to the heat stress respondents in 2009. The preliminary results show that

heat stress data are valid and useful to publish with the analysis and caveats as produced for this

paper submitted to BMJOpen.

“…Questions related to heat stress were as follows: “How often did the hot period this year



per month’, ‘1-6 times per week’, and ‘every day’. In this study, heat interference means

heat stress causing an uncomfortable feeling when doing those daily activities. For

analysis, we grouped self-reported heat stress into ‘never’, ‘sometimes’ (1-3 times per

month), and ‘often’ (1-6 times per week or every day)….”

3) Similarly, it may be unreliable for just using two questions from SF8 to measure the physical and

mental health impacts of heat. Discussion should be expanded.

We expanded the 3rd paragraph of the Discussion (in page 11), including…..

“…Elsewhere we have completed detailed analyses of associations between heat stress

and self-reported health outcomes in the cohort using the questions from SF8 (Tawatsupa

et al., 2010). Our studied outcomes in this report were holistic fundamental measures of

health…..”

4) Some relevant studies have already been conducted in Thailand (e.g., refs 10, 18-20 and Guo

et al, 2012), and the authors should discuss if their results are consistent with previous findings,

even though different studies focused on different health outcomes.

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We added one paragraph in the Discussion section (6th Paragraph) in page 12.

“…In our study, we found that heat stress in Thailand is not only a problem at work but also

heat stress interferes with other daily activities including sleeping, daily travel, housework

and exercise. The results of our study complement other Thai research about adverse

effects of heat. One recent report shows that heat stress in Thailand is a very serious

problem in a wide variety of work settings (Langkulsen et al., 2010). McMichael et al (2008)

and Guo et al (2012) found a temperature–mortality association and Pudpong et al (2011)

found heat related excess hospital admissions. Worker studies in Thailand related

occupational heat stress, kidney disease and psychological distress (Tawatsupa et al.,

2010, Tawatsupa et al., 2012b)…”

.------------------------------------------

3. Reviewer: Patrizia Schifano

1) The study is a cross-sectional study, based on a self administered questionnaire. The

questionnaire contains questions on "perception of the effect of heat on daily activities" and on

health outcomes. I would suggest to reformulate the objective of the paper, specifying they are

measuring the association between the perceived interference of heat stress on daily activities and

health outcomes. No direct measure of the exposure is taken.

Here, we added the word “self-reported” for heat stress interference in the objective of the

Abstract (Page 2).

“…Objectives: This study aims to examine the association between self-reported hot

season heat stress interference with daily activities (sleeping, work, travel, housework,

exercise) and three graded holistic health and wellbeing outcomes (energy, emotions, life

satisfaction)…”

And in the Article summary (Page 3)

“…To examine the association between self-reported heat stress interference with daily

activities (sleeping, work, travel, housework, exercise) during hot season and three graded

holistic health outcomes (energy, emotions, life satisfaction) in Thailand..”

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2) Furthermore the question on the interference between heat stress and daily activity is referred to

the whole year. Why didn't they restrict the reference period to the hot season? Alternatively they

could have repeated the question referring it separately to the hot season and the cold

season. Also questions revealing the health status are referred to a different period (one is referred

to the all-life time period, and the other two to the last month, and we don't know if this "last month"

was in the hot season or not. Assuming that heat stress can influence the perception of their

status, this might be important.

As we mentioned in the Methods (page 5) and Discussion section (page 11) that the heat

stress and health outcomes questions were in different parts of questionnaire, the respondents

could not easily link in their mind so answers on these issues were independent.

For heat stress question, we do not have detailed information on the date or season when

respondents answered the questions as our cohort data were collected by mailing continuously

during the year of study (in 2009). Although, the heat stress question did refer specifically to the

hot period within that year, tropical Thailand in general has hot and humid weather almost all year

round and not much variation within a year. We believe that the self-reported heat stress can give

information on frequency of heat interference during the study period (times per month or week).

For the health outcome measurements, the reason to use the period of past four weeks is to

prevent the recall-bias of self-reported health outcomes. In this study, the period of the past four

weeks was used according to the standard Medical Outcomes Short Form Instrument (SF8). Thus,

it would be complex to classify in more detail of hot and cold season and our baseline

questionnaire was very broad and was 20 pages long. We have done our best to utilise and

classify the heat stress related information gathered.

3) It is well known that some subjects are more susceptible than others to heat. In many studies

the elderly represents the part of the population more susceptible to the negative effect of heat on

health. The studied cohort is composed mainly by very young. This should be stressed more in the

paper.

This is a very helpful point. Our results showed heat stress and health impacts in a national

group of young and middle-aged Thai adults. We are aware that age effects heat stress and health

outcomes relationships so age was considered as a confounder in our analysis. Here we added a

sentence in the Abstract (page 2) and Discussion section (last paragraph in page 13) showing our

concern about heat stress effects in the elderly in the future;

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“…We conclude that Thai populations are at high risk of heat stress during daily activities.

Also, in Thailand an anticipated increase in temperature from climate change plus the

ageing and urbanisation of the population could significantly increase heat impacts on

health and wellbeing. There is a need for improvements in public health surveillance and

public awareness regarding the risks of heat stress which hitherto have been considered

unremarkable in such a tropical environment.”

-----------------------------------

Reference

Guo, Y., Punnasiri, K. & Tong, S. 2012. Effects of temperature on mortality in chiang mai city, thailand: A

time series study. Environmental Health, 11, 36.

Langkulsen, U., Vichit-Vadakan, N. & Taptagaporn, S. 2010. Health impact of climate change on

occupational health and productivity in thailand. Global Health Action, 3. DOI:10.3402/gha.v3i0.5607.

Mcmichael, A. J., Wilkinson, P., Kovats, R. S., Pattenden, S., Hajat, S., Armstrong, B., Vajanapoom, N.,

Niciu, E. M., Mahomed, H., Kingkeow, C., Kosnik, M., O'neill, M. S., Romieu, I., Ramirez-Aguilar, M.,

Barreto, M. L., Gouveia, N. & Nikiforov, B. 2008. International study of temperature, heat and urban

mortality: The 'isothurm' project. International Journal of Epidemiology, 37, 1121-31.

10.1093/ije/dyn086.

Pudpong, N. & Hajat, S. 2011. High temperature effects on out-patient visits and hospital admissions in

chiang mai, thailand. Science of the Total Environment, 409, 5260–5267.

10.1016/j.scitotenv.2011.09.005.

Tawatsupa, B., Dear, K., Kjellstrom, T. & Sleigh, A. 2012a. The association between temperature and

mortality in tropical middle income thailand from 1999 to 2008. Canberra: National Centre for

Epidemiology and Population Health.

Tawatsupa, B., Lim, L. L.-Y., Kjellstrom, T., Seubsman, S., Sleigh, A. & The Thai Cohort Study Team 2010.

The association between overall health, psychological distress, and occupational heat stress among

a large national cohort of 40,913 thai workers. Global Health Action, 3. 10.3402/gha.v3i0.534.

Tawatsupa, B., Lim, L. L.-Y., Kjellstrom, T., Seubsman, S., Sleigh, A. & The Thai Cohort Study Team 2012b.

Association between occupational heat stress and kidney disease among 37,816 workers in the thai

cohort study (tcs). Journal of Epidemiology, 22. 10.2188/jea.JE20110082.

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Section/Topic Item




what was found

2

Introduction



Methods




5

Participants

6




6

Data sources/

measurement



one group

6

(Our heat exposed group include respondents who

reported heat interfere their daily activities at 1-6 times

per week or every day. An unexposed group include

those who reported never experienced heat or 1-3 times

per month)





7


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Results




8





8






9




-


analyses

10

Discussion




11



11


Other information

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17





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Journal: BMJ Open

Manuscript ID: bmjopen-2012-001396.R2


Date Submitted by the Author: 03-Oct-2012









jopen.bmj.com

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Tawatsupa Page 1












Benjawan Tawatsupa,




Tel: +61 2 6125 5615; Fax: +61 2 6125 0740










Yiengprugsawan.


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Abstract









risk transition.







and low life satisfaction) associated with increasing frequency of heat stress interfering with









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Article summary

• Article focus:




in Thailand.

• Key messages:


problems, and low life satisfaction) associated with increasing frequency of

heat stress interfering with daily activities.













social attributes.

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Introduction







countries.(6)














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the general Thai population. Here we report an investigation of association between heat

stress interference with daily activities and health and wellbeing in a large national cohort of

young and middle aged Thai adults.

Methods

Study population

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all participants.

Results









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Discussion

Our study shows that climate-related heat stress in tropical Thailand associated with self-

reported health and wellbeing if the heat interfered with daily activities such as sleep,


Thai adults, mostly doing paid work, with a little over half residing in urban areas. These

cohort members are active and over 20% report often experiencing heat interference for daily

activities during the hot season. Daily travel and work were sources of heat stress more often

than other activities, probably because they involve time spent in traffic or outdoors during

hot periods. Other activities such as housework have less heat stress than daily travel and

work, perhaps because these activities are home-based where air-conditioning or other

ventilation is available.

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We found those who report higher levels of heat stress interference with daily activities tend

to also be the ones who have adverse health and wellbeing outcomes (low life satisfaction,

low energy level, and worse emotional problems). Odds Ratios of heat stress effects across all

daily activities for emotional problems are between 1·55 and 4·81 and in general are worse

than energy level effects (between 1·31 and 2·91) and life satisfaction effects (between 1·10

and 2·49). The worst health outcomes were for heat stress while sleeping followed by heat

stress for daily travel, work, housework and exercise.

Our data are based on self-report by educated Thais and we note that questions on heat stress

and health outcomes were in different parts of the questionnaire. Findings show strong and

highly consistent trends especially for adverse health effects of frequent heat interference

during sleep, daily travel, and work. Elsewhere we have completed detailed analyses of

associations between heat stress and self-reported health outcomes in the cohort using the

questions from SF8 (10). Our studied outcomes in this report were holistic fundamental

measures of health. We can expect that those who had abnormal findings would also (already

or eventually) manifest other more specific chronic diseases such as depression, obesity,

hypertension, and kidney disease. If so, the eventual burden of heat-related disease will be

higher than currently recognized.(27-29)







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distress.(10, 20)

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One limitation of this study is that it could not directly establish that health and wellbeing

outcomes arose as a result of heat stress. Interpreting causality between heat stress exposure

and health and wellbeing outcomes is complex in a cross-sectional study as we cannot be

completely sure that heat stress preceded their health condition and wellbeing. Also, the

source of the heat stress was not reported and we could not make direct measurements of heat

stress exposure and health and wellbeing outcomes. Another limitation of this study arose

because people answered the questionnaire at different times of the year (but most in March to

July - the hot period). The questions on physical and emotional health assessed the previous

four weeks so most (almost all) were answering for the hot period.

The strength of this study is its large scale with participation from a national group of adults

embedded in the socioeconomic mainstream of Thai society. Other strengths include the

comprehensive questionnaire which captures a detailed assessment of health and an array of

geodemographic, environmental and social attributes. Also, the cohort has been set up for

future longitudinal analysis which will provide better insight into causal pathways between

heat stress and subsequent health outcomes in the long run.







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Tables




Sex Male 45.3

Female 54.8

Age (year) ≤ 29 27.4

30-39 42.6

40+ 30.0


Never married 37.9




10,001-20,000 22.4

20,001-30,000 35.7

>30,000 23.1



Seeking work 2.2

Others 17.3




Regular smokers 7.7




Normal (18.5-22.9) 49.5


Obese (25+) 22.1


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Daily activities

N = 60,569



Sleeping 15.7 24.3 32.5 27.4

Housework 1.3 37.1 31.7 29.9

Daily travel 3.0 33.7 25.8 37.5

Work 14.0 30.3 21.2 34.5

Exercise 0.8 43.1 30.1 25.9



Outcomes

N = 60,569

%



8 (high) 28.8

6-7 (medium) 21.7



very much 14.9

quite a lot 44.0

some 32.0



not at all 11.3

slightly 48.4

moderately 25.8


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heat interference

category


% Life satisfaction


% Energy level

in the past 4 weeks


in the past 4 weeks

9-10

highest

8

high

6-7

medium

0-5

low



moderate

extreme

Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)

never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6

sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3

often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9

Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)

never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7

sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4

often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9

Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)

never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2

sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4

often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0

Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)

never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6

sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9

often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7

Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)

never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2

sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9

often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2

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Heat

interference

category

N=60,569



high

vs

highest

medium

vs

highest

low

vs

highest

quite a lot

vs

very much

some

vs

very much

little/none

vs

very much

slightly

vs

not at all

moderate

vs

not at all

extreme

vs

not at all

Sleep


sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]

often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]

Housework


sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]

often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]

Daily travel


sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]

often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]

Work


sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]

often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]

Exercise


sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]

often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]




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Acknowledgments









Competing interests









Data Sharing: Statistical code in Stata, and dataset available from the corresponding

author at [email protected]. All Participants gave informed consent and the

presented data in this manuscript are anonymous.

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Reference lists

1. Confalonieri U, Menne B, Akhtar R, et al. Human Health. Climate change 2007: Impacts, adaptation and vulnerability, contribution of working group II to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press; 2007 [cited 2012 13 March]; Available from: http://www.ipcc-wg2.org




5. Bi P, Williams S, Loughnan M, et al. The effects of extreme heat on human mortality and morbidity in Australia: Implications for public health. Asia Pac J Public Health. 2011;23(2 Suppl):27S-36S.





10. Tawatsupa B, Lim LL-Y, Kjellstrom T, et al. The association between overall health, psychological distress, and occupational heat stress among a large national cohort of 40,913 Thai workers. Glob Health Action. 2010;3(5034).



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14. Kjellstrom T, Gabrysch S, Lemke B, et al. The "Hothaps" program for assessing climate change impacts on occupational health and productivity: an invitation to carry out field studies Glob Health Action. 2009;2.




18. McMichael AJ, Wilkinson P, Kovats RS, et al. International study of temperature, heat and urban mortality: the 'ISOTHURM' project. Int J Epidemiol. 2008 Oct;37(5):1121-31.


20. Tawatsupa B, Lim LL-Y, Kjellstrom T, et al. Association between occupational heat stress and kidney disease among 37,816 workers in the Thai Cohort Study (TCS). J Epidemiol. 2012;22.



23. Cummins RA, Eckersley R, Pallant J, et al. Developing a National Index of Subjective Wellbeing: The Australian Unity Wellbeing Index. Soc Indic Res. 2003;64(2):159-90.

24. Yiengprugsawan V, Seubsman S, Khamman S, et al. Personal wellbeing index in a national cohort of 87,134 Thai adults. Soc Indic Res. 2010;98(2):201-15.


26. Kanazawa M, Yoshiike N, Osaka T, et al. Criteria and classification of obesity in Japan and Asia-Oceania Asia Pac J Clin Nutr. 2002;11:S732-S7.

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29. Kjellstrom T, Butler AJ, Lucas RM, et al. Public health impact of global heating due to climate change: potential effects on chronic non-communicable diseases. Int J Public Health. 2010;55:97-103.




33. Hansen AL, Bi P, Nitschke M, et al. The effect of heat waves on mental health in a temperate Australian city. Environ Health Perspect. 2008;116(10):1369 - 75.

34. Anderson C, Anderson K, Dorr N, et al. Temperature and aggression Adv Experimental Social Psychology. 2000;32:63-133.


36. Maes M, De Meyer F, Thompson P, et al. Synchronized annual rhythms in violent suicide rate, ambient temperature and the light-dark span. Acta Psychiatr Scand. 1994 Nov;90(5):391-6.

37. Bouchama A, Dehbi M, Mohamed G, et al. Prognostic factors in heat wave-related deaths: A meta-analysis. Arch Intern Med. 2007;167(20):2170-6.


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Section/Topic Item




what was found

2

Introduction



Methods




6

Participants

6




7

Data sources/

measurement



one group

7





7






Results

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8





8






9




-


analyses

10

Discussion




13



11


Other information



18





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Tawatsupa Page 1



Benjawan Tawatsupa1, 2,*

, Vasoontara Yiengprugsawan1, Tord Kjellstrom

1, 3,









Benjawan Tawatsupa,




Tel: +61 2 6125 5615; Fax: +61 2 6125 0740










Yiengprugsawan.


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Abstract









risk transition.







and low life satisfaction) associated with increasing frequency of heat stress interfering with









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Article summary

• Article focus:




in Thailand.

• Key messages:


problems, and low life satisfaction) associated with increasing frequency of

heat stress interfering with daily activities.













social attributes.

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Introduction







countries.(6)














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the general Thai population. Here we report an investigation of association between heat

stress interference with daily activities and health and wellbeing in a large national cohort of

young and middle aged Thai adults.

Methods

Study population

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all participants.

Results









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Discussion

Our study shows that climate-related heat stress in tropical Thailand associated with self-

reported health and wellbeing if the heat interfered with daily activities such as sleep,


Thai adults, mostly doing paid work, with a little over half residing in urban areas. These

cohort members are active and over 20% report often experiencing heat interference for daily

activities during the hot season. Daily travel and work were sources of heat stress more often

than other activities, probably because they involve time spent in traffic or outdoors during

hot periods. Other activities such as housework have less heat stress than daily travel and

work, perhaps because these activities are home-based where air-conditioning or other

ventilation is available.

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We found those who report higher levels of heat stress interference with daily activities tend

to also be the ones who have adverse health and wellbeing outcomes (low life satisfaction,

low energy level, and worse emotional problems). Odds Ratios of heat stress effects across all

daily activities for emotional problems are between 1·55 and 4·81 and in general are worse

than energy level effects (between 1·31 and 2·91) and life satisfaction effects (between 1·10

and 2·49). The worst health outcomes were for heat stress while sleeping followed by heat

stress for daily travel, work, housework and exercise.

Our data are based on self-report by educated Thais and we note that questions on heat stress

and health outcomes were in different parts of the questionnaire. Findings show strong and

highly consistent trends especially for adverse health effects of frequent heat interference

during sleep, daily travel, and work. Elsewhere we have completed detailed analyses of

associations between heat stress and self-reported health outcomes in the cohort using the

questions from SF8 (10). Our studied outcomes in this report were holistic fundamental

measures of health. We can expect that those who had abnormal findings would also (already

or eventually) manifest other more specific chronic diseases such as depression, obesity,

hypertension, and kidney disease. If so, the eventual burden of heat-related disease will be

higher than currently recognized.(27-29)







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distress.(10, 20)

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One limitation of this study is that it could not directly establish that health and wellbeing

outcomes arose as a result of heat stress. Interpreting causality between heat stress exposure

and health and wellbeing outcomes is complex in a cross-sectional study as we cannot be

completely sure that heat stress preceded their health condition and wellbeing. Also, the

source of the heat stress was not reported and we could not make direct measurements of heat

stress exposure and health and wellbeing outcomes. Another limitation of this study arose

because people answered the questionnaire at different times of the year (but most in March to

July - the hot period). The questions on physical and emotional health assessed the previous

four weeks so most (almost all) were answering for the hot period.

The strength of this study is its large scale with participation from a national group of adults

embedded in the socioeconomic mainstream of Thai society. Other strengths include the

comprehensive questionnaire which captures a detailed assessment of health and an array of

geodemographic, environmental and social attributes. Also, the cohort has been set up for

future longitudinal analysis which will provide better insight into causal pathways between

heat stress and subsequent health outcomes in the long run.







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Tables




Sex Male 45.3

Female 54.8

Age (year) ≤ 29 27.4

30-39 42.6

40+ 30.0


Never married 37.9




10,001-20,000 22.4

20,001-30,000 35.7

>30,000 23.1



Seeking work 2.2

Others 17.3




Regular smokers 7.7




Normal (18.5-22.9) 49.5


Obese (25+) 22.1


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Daily activities

N = 60,569



Sleeping 15.7 24.3 32.5 27.4

Housework 1.3 37.1 31.7 29.9

Daily travel 3.0 33.7 25.8 37.5

Work 14.0 30.3 21.2 34.5

Exercise 0.8 43.1 30.1 25.9



Outcomes

N = 60,569

%



8 (high) 28.8

6-7 (medium) 21.7



very much 14.9

quite a lot 44.0

some 32.0



not at all 11.3

slightly 48.4

moderately 25.8


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heat interference

category


% Life satisfaction


% Energy level

in the past 4 weeks


in the past 4 weeks

9-10

highest

8

high

6-7

medium

0-5

low



moderate

extreme

Sleep (n) (22132) (17024) (12770) (7052) (8833) (26142) (18968) (5378) (6684) (28752) (15297) (8603)

never 29.5 22.9 19.7 19.7 33.2 25.3 20.2 19.6 38.6 25.4 19.3 18.6

sometimes 30.2 34.7 35.0 30.1 29.9 34.0 32.5 29.4 25.5 34.3 33.9 29.3

often 22.2 25.7 32.2 39.8 22.0 24.5 31.5 36.1 16.4 24.0 32.3 38.9

Housework (n) (22094) (16992) (12748) (7029) (8827) (26085) (18924) (5364) (6668) (28683) (15273) (8590)

never 43.6 36.2 31.0 30.4 46.6 39.1 31.9 30.7 53.2 38.9 31.1 29.7

sometimes 28.0 34.4 35.4 30.2 26.1 32.6 33.3 31.0 24.2 32.8 33.6 30.4

often 27.0 28.2 32.5 38.4 25.9 27.1 33.6 36.8 20.8 27.1 33.9 38.9

Daily travel (n) (22111) (16994) (12739) (7018) (8829) (26082) (18931) (5355) (6668) (28692) (15275) (8576)

never 40.1 33.2 27.5 26.1 42.7 35.6 28.3 28.0 49.7 35.7 27.8 25.2

sometimes 24.2 27.6 27.4 23.3 23.1 27.1 26.0 23.1 21.6 27.3 16.7 22.4

often 32.4 35.8 42.6 48.7 31.4 34.1 42.6 46.1 24.7 34.0 42.7 50.0

Work (n) (22100) (17000) (12744) (7018) (8831) (26101) (18923) (5362) (6668) (28706) (15279) (8579)

never 36.4 29.6 24.4 23.9 38.9 32.0 25.7 24.2 45.5 32.1 24.6 22.6

sometimes 20.3 21.8 22.8 19.2 19.1 22.5 21.0 19.1 17.1 22.5 22.0 18.9

often 29.8 33.2 38.5 44.9 30.0 31.4 38.7 41.5 23.7 31.1 39.7 44.7

Exercise (n) (22080) (16966) (12724) (7016) (8825) (26065) (18895) (5333) (6664) (28668) (15239) (8561)

never 46.8 42.6 38.8 41.0 49.8 43.5 39.7 42.8 55.2 43.9 38.1 40.2

sometimes 27.8 31.8 33.0 28.2 24.9 31.1 31.7 28.5 23.7 30.8 32.4 28.9

often 24.6 24.8 27.4 30.2 24.7 24.6 27.7 27.9 20.1 24.5 28.8 30.2

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Heat

interference

category

N=60,569



high

vs

highest

medium

vs

highest

low

vs

highest

quite a lot

vs

very much

some

vs

very much

little/none

vs

very much

slightly

vs

not at all

moderate

vs

not at all

extreme

vs

not at all

Sleep


sometimes 1.46 [1.37-1.55 ] 1.66 [1.55-1.78] 1.42 [1.30-1.55] 1.48 [1.38-1.59] 1.76 [1.63-1.90] 1.65 [1.48-1.84] 1.94[1.80-2.10] 2.48 [2.28-2.70] 2.23 [2.02-2.46]

often 1.50 [1.41-1.60] 2.10 [1.95-2.25] 2.49 [2.28-2.71] 1.52 [1.40-1.64] 2.44 [2.25-2.64] 2.91 [2.61-3.25] 2.27 [2.07-2.48] 3.86 [3.50-4.26] 4.81 [4.32-5.36]

Housework


sometimes 1.42 [1.35-1.50] 1.65 [1.56-1.76] 1.44 [1.33-1.56] 1.46 [1.36-1.56] 1.76 [1.64-1.89] 1.70 [1.54-1.87] 1.79 [1.66-1.93] 2.21 [2.04-2.39] 2.05 [1.87-2.24]

often 1.32 [1.25-1.40] 1.79 [1.68-1.90] 2.11 [1.95-2.28] 1.31 [1.22-1.40] 2.04 [1.89-2.19] 2.34 [2.13-2.58] 1.82 [1.68-1.96] 2.86 [2.62-3.11] 3.35 [3.05-3.67]

Daily travel


sometimes 1.36 [1.28-1.44] 1.60 [1.49-1.70] 1.36 [1.25-1.49] 1.40 [1.30-1.50] 1.66 [1.54-1.79] 1.51 [1.35-1.67] 1.64 [164-1.77] 2.00 [1.84-2.18] 1.78 [1.61-1.97]

often 1.33 [126-1.41] 1.82 [1.72-1.94] 2.13 [1.97-2.30] 1.36 [1.28-1.46] 2.13 [1.98-2.28] 2.30 [2.10-2.53] 1.85 [1.71-1.99] 2.82 [2.60-3.06] 3.51 [3.21-3.85]

Work


sometimes 1.32 [1.24-1.40] 1.63 [1.52-1.75] 1.40 [1.28-1.54] 1.40 [1.30-1.51] 1.65 [1.52-1.80] 1.64 [1.46-1.84] 1.78 [1.63-1.93] 2.22 [2.03-2.44] 2.08 [1.87-2.32]

often 1.37 [1.30-1.45] 1.87 [1.75-1.99] 2.17 [2.01-2.36] 1.36 [1.27-1.45] 2.13 [1.98-2.29] 2.45 [2.22-2.71] 1.85 [1.71-1.99] 2.96 [2.73-3.24] 3.64 [3.31-4.00]

Exercise


sometimes 1.26 [1.19-1.33] 1.40 [1.32-1.48] 1.10 [1.02-1.18] 1.41 [1.32-1.51] 1.58 [1.48-1.70] 1.33 [1.21-1.46] 1.57[1.45-1.71] 1.90[1.75-2.05] 1.55 [1.42-1.69]

often 1.17 [1.11-1.24] 1.42 [1.33-1.51] 1.38 [1.28-1.49] 1.24 [1.16-1.33] 1.59 [1.48-1.71] 1.57 [143-1.73] 1.58 [1.46-1.71] 2.16 [1.98-2.35] 2.14 [1.94-2.35]




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Acknowledgments









Competing interests









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Reference lists

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10. Tawatsupa B, Lim LL-Y, Kjellstrom T, Seubsman S, Sleigh A, the Thai Cohort Study team. The association between overall health, psychological distress, and occupational heat stress among a large national cohort of 40,913 Thai workers. Glob Health Action. 2010;3(5034).



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