BMJ Open · 69 work schedules between the day and night (i.e., rotating shift work). Previous...
Transcript of BMJ Open · 69 work schedules between the day and night (i.e., rotating shift work). Previous...
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Association of eating behaviors with diurnal preference and rotating shift work in Japanese female nurses: a cross-
sectional study
Journal: BMJ Open
Manuscript ID bmjopen-2016-011987
Article Type: Research
Date Submitted by the Author: 21-Mar-2016
Complete List of Authors: Yoshizaki, Takahiro; Toyo University, Faculty of Food and Nutritional Sciences Kawano, Yukari; Tokyo University of Agriculture, Department of Nutritional
Science, Faculty of Applied Bio-Science Noguchi, Osamu; Ome City General Hospital, Department of Gastroenterology Onishi, Junko; Ome City General Hospital, Department of Nursing Teramoto, Reiko; Ome City General Hospital, Department of Clinical Nutrition Sunami, Ayaka; Tokyo University of Agriculture, Graduate School of Agriculture Yokoyama, Yuri; Tokyo University of Agriculture, Graduate School of Agriculture Tada, Yuki; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science
Hida, Azumi; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science Togo, Fumiharu; The University of Tokyo, Graduate School of Education
<b>Primary Subject Heading</b>:
Nutrition and metabolism
Secondary Subject Heading: Epidemiology, Occupational and environmental medicine, Public health
Keywords: Dietary habits, Chronotype, Rotating shift worker, Diurnal preference
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Association of eating behaviors with diurnal preference and 1
rotating shift work in Japanese female nurses: a 2
cross-sectional study 3
4
Takahiro Yoshizaki1, Yukari Kawano
2, Osamu Noguchi
3, Junko Onishi
4, Reiko Teramoto
5, 5
Ayaka Sunami6, Yuri Yokoyama
6, Yuki Tada
2, Azumi Hida
2, Fumiharu Togo
7 6
7
1Faculty of Food and Nutritional Sciences, Toyo University, Gunma, Japan 8
2Department of Nutritional Science, Faculty of Applied Bio-Science, Tokyo University of 9
Agriculture, Tokyo, Japan 10
3Department of Gastroenterology, Ome City General Hospital, Tokyo, Japan 11
4Department of Nursing, Ome City General Hospital, Tokyo, Japan 12
5Department of Clinical Nutrition, Ome City General Hospital, Tokyo, Japan 13
6Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan 14
7Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo, 15
Tokyo, Japan 16
17
Running head: Rotating Shift Work and Eating Behaviors 18
Address correspondence to: 19
Takahiro Yoshizaki, Ph.D. 20
Faculty of Food and Nutritional Sciences, Toyo University 21
1-1-1 Izumino, Oura-gun, Itakura-machi, Gunma 374-0193, Japan 22
Tel: +81-276-82-9012 Fax: +81-276-82-9000 E-mail: [email protected] 23
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ABSTRACT 24
Objectives 25
Our study examines the relationships between work schedule and eating behaviors, and 26
considers whether diurnal preference could explain the relationship. 27
Methods 28
Japanese female nurses were studied (39 day workers and 123 rotating shift workers, aged 21–29
63) using self-administered questionnaires. The questionnaires assessed eating behaviors, 30
diurnal preference, and demographic characteristics. Sakata’s Eating Behavior Questionnaire 31
consists of 55 items, where higher scores signify higher probabilities of obesity, and was used 32
to obtain scores for the levels of obesity-related eating behaviors, including cognition of 33
constitution, motivation for eating, eating as a diversion, feeling of satiety, eating style, meal 34
contents, and temporal eating patterns. A Japanese version of the Morningness-Eveningness 35
questionnaire was used to measure self-rated preference for a morning activity pattern 36
(Morning-type) or evening activity pattern (Evening-type). 37
Results 38
The scores for meal contents and temporal eating patterns in rotating shift workers were 39
significantly higher than those in day workers. The ME-score of rotating shift workers was 40
significantly lower, indicating a tendency for more Evening types among rotating shift workers. 41
Multivariable linear regression analyses revealed that the correlation with the ME-score was 42
significantly negative for the score for temporal eating patterns and showed a negative 43
association with the score for meal contents at a trend level, while current work shift was not 44
significantly correlated with the scores. 45
Conclusions 46
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These results suggest that rotating shift work is associated with a more unbalanced diet and 47
abnormal temporal eating patterns and that the associations may be mediated and/or modulated 48
partly by diurnal preference. 49
50
Keywords: Dietary habits; Chronotype; Rotating shift worker 51
52
STRENGTHS and LIMITATIONS of THIS STUDY 53
・There are few studies that have clarified whether the difference of diurnal preference explains 54
changes in eating behaviors in rotating shift workers. 55
・The aim of the present study was to elucidate the association between rotating shift work and 56
obesity-related eating behaviors, considering the diurnal preference, among Japanese female 57
nurses. 58
・Rotating shift work was associated with a more unbalanced diet and abnormal temporal eating 59
patterns, and the associations may be mediated and/or modulated partly by being of the 60
Evening type. 61
・These findings have important implications for the development of novel strategies for 62
preventing excessive weight gain in rotating shift workers. 63
64
65
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1. INTRODUCTION 66
A super-aged society leads to an increase in the social demand for nurses in medical facilities. 67
Among them, health problems can be caused by severe working conditions such as shifting of 68
work schedules between the day and night ( i.e., rotating shift work). Previous studies have 69
suggested that rotating shift work is related to higher risks of health problems, including 70
obesity, increases in body mass index (BMI), and adiposity with abnormal metabolism, 71
compared with fixed day work. 1-3
One of the possible factors for increasing the risks of these 72
health problems in rotating shift workers is their altered eating behavior. 4 5
Our previous 73
studies demonstrated that female workers who engaged in rotating shift work consumed more 74
sugar-sweetened beverages and snacks than day workers, 6 7
and that the rate of subjects who 75
reported skipping breakfast almost everyday (80–100%) on days on the day shift was 76
significantly higher in rotating shift workers compared with day workers. 8 A recent study by 77
another group has also indicated unbalanced dietary intake, such as greater intake of fats and 78
oils and lower intake of vegetables, in rotating shift workers compared with day workers. 9 79
However, it is unclear which aspects of obesity-related eating behavior change in rotating shift 80
workers, and which factors contribute to the altered eating behaviors in rotating shift workers. 81
82
One plausible factor contributing to the altered eating behaviors in rotating shift workers is a 83
changed circadian rhythm. Our previous study revealed that rotating shift workers had a 84
significant phase delay in the 24-h rhythm of cardiac autonomic nervous system activity 85
compared with fixed day workers, 10
suggesting a phase delay of the circadian rhythm among 86
rotating shift workers. The endogenous circadian clocks, controlled by the master circadian 87
clock in the suprachiasmatic nuclei of the hypothalamus, play a significant role in regulating a 88
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number of circadian and daily physiological rhythms, including feeding behavior. 11
For 89
example, a human laboratory study showed that the circadian clock regulated hunger and 90
appetite independently of the fasting-feeding rhythm and the sleep-wake cycle, 12
indicating 91
that the phase delay of the circadian clock might modify the timing of eating. Moreover, a 92
recent study revealed that a late midpoint of nocturnal sleep was associated with increases in 93
energy intake from undesirable dietary contents such as alcoholic beverages, confectioneries, 94
fats and oils, and meats in individuals who did not engage in night shift work. 13
Despite these 95
available data, which suggest a possibility of a close association between eating behavior and 96
the circadian clock, there are few studies that have clarified whether the association explains 97
changes in eating behaviors in rotating shift workers. 98
99
To investigate epidemiologically the phase of the circadian clock during daily life, individual 100
preference in the phase of the sleep-wake cycle (i.e. , diurnal preference or chronotype), which 101
may be different from the actual sleep-wake cycle during daily life, was assessed using the 102
Japanese version of the Morningness-Eveningness questionnaire by Torsvall and Akerstedt. 14
103
15 Diurnal preference (e.g., Evening type or Morning type) are attr ibuted to differences in the 104
phase of the circadian clock. 16
Therefore, the aim of the present study was to elucidate the 105
association between rotating shift work and obesity-related eating behaviors, considering the 106
diurnal preference, among Japanese female nurses. Dietary habits were investigated using 107
Sakata’s Eating Behavior Questionnaire, which is included in the Guidelines for the 108
management of obesity disease in Japan. 17
Characteristics of eating behavior among 109
overweight individuals were extracted from an interview survey and compiled to produce the 110
questionnaire. 18
Our hypothesis was that rotating shift workers would have obesity-related 111
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eating behaviors associated with meal contents (e.g., greater intake of specific nutrients) and 112
temporal eating patterns (e.g., skipping breakfast and/or late dinner), and that diurnal 113
preference would partially explain the associations between rotating shift work and 114
obesity-related eating behaviors. 115
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2. METHODS 116
2.1 Participants 117
The study population consisted of nurses working at a general hospital in the center of Ome 118
city. Ome city is located in the west side of the Tokyo metropolitan area and is the fifth 119
largest city in the metropolis. Urbanization and industrialization are present in the region of 120
the plain, while districts in the hilly area in the western region of the city have rural 121
populations. A total of 506 nurses were handed the questionnaires by the chief nursing officer 122
on each ward. The purpose of this study and data handling procedures were described in a 123
cover letter with the questionnaire. Agreement to participate in this study was assumed on the 124
basis of receipt of an anonymous questionnaire. A total of 218 nurses (43.1%; age 19–63 yr) 125
responded. Among them, 56 were excluded from the analysis because of missing data [age 126
(n=2), current work schedules (n=6), residential status (n=1), marital status (n=2), years of 127
experience as a rotating shift worker (n=23), smoking status (n=2), alcohol status (n=4), 128
number of night shifts in the previous month (n=6), and the questionnaire about diurnal 129
preference (n=13)]. Because the scoring method for the questionnaire about obesity-related 130
eating behavior was different for men and women, 19
we decided to exclude the small number 131
of data from male nurses (n=20). As a result, 162 female nurses (39 day workers and 123 132
shift workers) were analyzed. Their mean total duration of experience in their current job was 133
12.2 ± 10.3 [SD] yr. In this study, individuals who worked only a fixed day shift (09:00–134
18:00 h) were defined as “day workers”, and those who worked both day shifts and night shifts 135
(18:00–09:00 h) in a rotating shift system as “rotating shift workers”. All the study 136
procedures were reviewed and approved by the Ethics Committee at the Tokyo University of 137
Agriculture (No. 1111). 138
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139
2.2 Assessments 140
A cross-sectional study using self-administered questionnaires on demographic characteristics, 141
diurnal preference and eating behavior was conducted in the general hospital at the beginning 142
of September 2012. Completed questionnaires were returned within two weeks. 143
Demographic characteristics of the participants included in the questionnaire were the 144
following: age, height, weight, current work schedule, years of experience in the current job 145
and as a rotating shift worker, marital status, residential status, smoking status, alcohol status, 146
and the number of night shifts in the previous month. Body mass index (BMI) was calculated 147
on the basis of self-reported height and weight [weight / height2 (kg / m
2)]. A Japanese 148
version of the Morningness-Eveningness questionnaire by Torsvall and Akerstedt, of which the 149
internal reliability has been confirmed, was used to measure self-rated preference for activity 150
in the morning or the evening. 14 15
Based on seven items about daily sleep habits or preference 151
consisting of 0–3 Likert scales, the Morningness-Eveningness score (ME-score) was calculated 152
(range: 7–28 points). A lower ME-score indicates a tendency for a greater preference for 153
activity in the evening (Evening type), while a higher ME-score indicates a greater preference 154
for activity in the morning (Morning type). The data about habitual eating behavior over the 155
previous one month was obtained from the response to Sakata’s Eating Behavior Questionnaire, 156
17 20 which was developed to detect obesity-related eating behavior. The details of the 157
contents of the questionnaire have been shown in previous studies. 17 18 20
In brief, each of the 158
55 items on eating habits is rated on a four-point scale ranging from “strongly disagree” to 159
“strongly agree”. These items are classified into the scores for seven areas regarding 160
cognition of constitution (range: 6–24), motivation for eating (range: 9–36), eating as a 161
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diversion (range: 4–16), feeling of satiety (range: 6–24), eating style (range: 5–20), meal 162
contents (range: 7–28), and temporal eating patterns (range: 8–32). Higher scores indicate 163
more improper eating behavior in terms of a higher probability of obesity. 21
164
165
2.3 Statistical analysis 166
After the normal distr ibution of variables had been tested by Kolmogorov-Smirnov test, the 167
t-test or Mann–Whitney U test and the χ2 test or Fisher 's exact test were used for continuous 168
and categorical variables, respectively, to compare the difference in demographic 169
characteristics, ME-score, and the scores for eating behavior between day workers and rotating 170
shift workers. For categorical variables, residuals between the observed and expected 171
frequencies were standardized to determine cells which were statistically different from 172
expected values. Simple and multivariable linear regression analyses (model 1) were 173
performed with each score for eating behavior (meal contents or temporal eating patterns) as 174
dependent variables, and current work schedule (0 = day work, 1 = rotating shift work) and 175
ME-score (continuous, in points) as independent variables. The model was extended (model 176
2) using demographic characteristics of the participants for covariate adjustment: age 177
(continuous, in years), years of experience as a rotating shift worker (continuous, in years), 178
marital status (0 = married, 1 = unmarried or divorced), residential status (0 = living alone, 1 = 179
not living alone), smoking status (“Do you smoke?”; 0 = no, 1 = yes), alcohol status (“Do you 180
drink alcohol?”; 0 = no, 1 = yes), and the number of night shifts in the previous month 181
(continuous, in days). All statistical analyses were performed with an SPSS statistical 182
software package (IBM SPSS 22.0 for Windows, SPSS Japan). P values less than 0.05 were 183
considered statistically significant using two-tailed tests. 184
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3. RESULTS 185
The demographic characteristics of day workers and rotating shift workers are shown in Table 186
1. Age was significantly higher in day workers compared with rotating shift workers (p < 187
0.05). The years of experience in the current work schedule were significantly more in day 188
workers compared with rotating shift workers (p < 0.05). Marital status and residential status 189
were significantly associated with the current work schedule (p < 0.05). ME-score for 190
rotating shift workers was significantly lower compared with day workers (p < 0.05), 191
indicating a tendency for more Evening types among rotating shift workers compared with day 192
workers. This significant difference was not attenuated after controlling for age as a 193
confounding variable (data not shown). 194
195
Table 1 Demographic characteristics of day workers and rotating 196
shift workers 197
Day workers Shift workers
P values
n=39 n=123
Age† (years) 44.2 ± 10.9 34.7 ± 8.7 < 0.001
Height†a
(cm) 156.7 ± 5.6 157.5 ± 5.5 0.175
Weight†b
(kg) 53.4 ± 8.3 53.8 ± 8.9 0.784
BMI†c
(kg/m2) 21.7 ± 2.7 21.7 ± 3.5 0.676
ME-score†§
(points) 20.8 ± 3.3 17.1 ± 4.0 < 0.001
Years of experience
Current work† (years) 17.4 ± 12.0 10.6 ± 9.2 0.002
Rotating shift work† (years) 11.8 ± 10.7 9.7 ± 8.7 0.652
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Number of night shifts (day/month) 0.0 ± 0.0 7.6 ± 3.1 -
Marital status‡ Married 32 ( 82 )
* 50 ( 41 )
0.001
Unmarried or divorced 7 ( 18 ) 73 ( 59 ) *
Residential status‡ Living alone 3 ( 8 ) 33 ( 27 )
*
0.014
Not living alone 36 ( 92 ) * 90 ( 73 )
Smoking status Yes 4 ( 10 ) 17 ( 14 )
0.785
No 35 ( 90 ) 106 ( 86 )
Alcohol status‡ Yes 21 ( 54 ) 51 ( 41 )
0.198
No 18 ( 46 ) 72 ( 59 )
198
Values are means ± standard deviation or number (%). 199
BMI, body mass index; ME-score, Morningness-Eveningness score 200 †Mann-Whitney U test 201
‡χ
2 test or Fisher's exact test (When p < 0.05, standardized residuals were determined for each 202
cell.) 203 *p < 0.05 204
§A lower ME-score is indicative of the Evening type. 205
aShift workers, n=120
206
bShift workers, n=118
207
cShift workers, n=118
208
209
The obesity-related eating behaviors of day workers and rotating shift workers are shown in 210
Table 2. The scores for meal contents and temporal eating patterns significantly differed 211
between the groups (p < 0.05), indicating an unbalanced diet and more irregular timing of 212
meals among rotating shift workers compared with day workers. Scores for other eating 213
behaviors did not differ between the groups (p > 0.05). 214
215
216
Table 2 Scores for habitual eating behavior in day workers and 217
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rotating shift workers 218
Normal Day workers Shift workers
p values
(Ref. 32) n=39 n=123
Cognition of constitution†a
(points) 14 14.3 ± 3.4 13.6 ± 3.7 0.328
Motivation for eating‡b
(points) 18 19.5 ± 4.9 18.8 ± 5.6 0.384
Eating as a diversion‡c
(points) 7 7.4 ± 2.4 7.1 ± 2.9 0.310
Feeling of satiety‡ (points) 10 10.9 ± 3.1 11.3 ± 3.2 0.427
Eating style‡ (points) 9 9.8 ± 3.5 9.7 ± 3.6 0.629
Meal contents‡ (points) 12 13.9 ± 3.9 15.6 ± 4.5 0.045
Temporal eating patterns‡d
(points) 16 16.5 ± 4.5 19.5 ± 4.8 0.001
219
Values are means ± standard deviation. 220
Higher scores indicate more improper eating behavior in terms of a higher probability of 221
obesity: Cognition of weight and constitution, having false recognition of and assumptions 222
about reasons for weight gain; Motivation for eating, having behavioral factors which can 223
induce over-eating; Eating as a diversion, being subject to psychological factors which increase 224
appetite (i.e., perceived mental stress); Feeling of satiety, being prone to have an appetite and 225
to eat as much as possible; Eating style, being prone to eat fast; Meal contents, having a 226
preference for a high fat diet and sweets (e.g., confectioneries and sweet buns); Temporal 227
eating patterns, irregularity of timing and number of meals taken during the day and delay in 228
timing of meals. 229 †t-test 230
‡Mann-Whitney U test 231
aShift workers, n=122
232
bShift workers, n=122
233
cDay workers, n=38
234
dShift workers, n=119
235
236
We examined the relationship between rotating shift work, ME-score, and scores for meal 237
contents and temporal eating patterns using simple and multivariable linear regression analyses. 238
Simple linear regression analyses (Table 3) showed that rotating shift work and a lower 239
ME-score were significantly (p < 0.05) associated with higher scores for meal contents and 240
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temporal eating patterns. Multivariable linear regression analyses (model 1) showed that the 241
ME-score was significantly (p < 0.05) associated with the score for meal contents, while the 242
effect of rotating shift work was attenuated to trend level (p < 0.1). Regarding temporal 243
eating patterns, the ME-score was significantly (p < 0.05) associated with the score, while 244
rotating shift work was not. In model 2, in which the variables of demographic characteristics 245
which significantly (p < 0.05) differed between the groups (i.e., age, years of experience as a 246
rotating shift worker, marital status, residential status, and number of night shifts per month) 247
and smoking and alcohol status were controlled, the correlations with the ME-score decreased 248
slightly but remained significantly negative (β = —0.329, p < 0.001) for temporal eating 249
patterns or at a trend level (β = —0.161, p = 0.082) for meal contents. 250
251
Table 3 Association of current shift schedule (rotating shift work) 252
and diurnal preference with scores for meal contents and temporal 253
eating patterns in multivariable linear regression models 254
Independent
variables
Unstandardized
coefficients
Standardized
coefficients p values
B SE β
Meal contents
Crude
Rotating shift work 1.689 0.804 0.164 0.037
ME-score —0.223 0.082 —0.210 0.007
Model 1
Rotating shift work 1.007 0.862 0.098 0.245
ME-score —0.183 0.089 —0.172 0.041
Model 2a
Rotating shift work 0.934 1.303 0.091 0.475
ME-score —0.171 0.098 —0.161 0.082
Temporal eating patterns
Crude
Rotating shift work 3.211 0.867 0.284 < 0.001
ME-score —0.465 0.086 —0.397 < 0.001
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Model 1
Rotating shift work 1.698 0.897 0.150 0.060
ME-score —0.395 0.093 —0.338 < 0.001
Model 2a
Rotating shift work 1.278 1.357 0.113 0.348
ME-score —0.384 0.101 —0.329 < 0.001 255 aAdjusted by age, years of experience as a rotating shift worker, marital status, residential 256
status, smoking status, alcohol status, and number of night shifts per month. Years of 257
experience in the current work schedule were not included in Model 2 because of a high level 258
of multicollinearity (Variance inflation factor = 8.101). 259
260
261
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4. DISCUSSION 262
Our cross-sectional study explored the association between rotating shift work and 263
obesity-related eating behaviors, considering diurnal preference, among Japanese female 264
nurses. As a result, the scores for meal contents and temporal eating patterns in rotating shift 265
workers were significantly higher than those in day workers. The ME-score of rotating shift 266
workers was significantly (p < 0.05) lower compared with day workers, indicating a tendency 267
for more Evening types among rotating shift workers. Multivariable linear regression 268
analyses revealed that the correlation with the ME-score was significantly negative (β = —269
0.329, p < 0.001) for the score for temporal eating patterns and showed a negative association 270
with the score for meal contents at a trend level (β = —0.161, p = 0.082), while current work 271
shift (i.e., rotating shift work) was not significantly correlated with the scores. These results 272
suggest that rotating shift work is associated with a more unbalanced diet and abnormal 273
temporal eating patterns and that the associations may be mediated and/or modulated partly by 274
diurnal preference (e.g. the Evening type). To the best of our knowledge, this is the first 275
study to show the associations between rotating shift work, diurnal preference, and eating 276
behavior. 277
278
Given the fact that the Evening type closely correlates with delays in the phase angle of the 279
circadian rhythm 16
and that the phase delay can be caused by light exposure and sleep/dark 280
schedules during nights on the days of the night shift, 22
our study indicates that being of the 281
Evening type, or the phase delay of the circadian rhythm, may correlate with altered eating 282
behavior in rotating shift workers. This indication is supported by previous studies. 10 23
For 283
example, one previous study revealed that rotating shift workers showed a phase delay in the 284
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circadian rhythm compared with day workers. 10
In addition, rotating shift workers have a 285
tendency for more Evening types compared with day workers, 8 24
which is consistent with our 286
results. We also demonstrated that a greater phase delay of the circadian rhythm was 287
associated with a later timing of breakfast among rotating shift workers. 23
However, causality 288
between diurnal preference or phase angle of the circadian rhythm and altered eating behavior 289
could not be examined, although these may have interactive effects. It should be explored in 290
future studies whether changes from the Evening type to the Morning type in diurnal 291
preference or the phase advance of the circadian rhythm would improve eating behavior in 292
rotating shift workers. 293
294
Our results show that rotating shift work is associated with higher scores for meal contents and 295
temporal eating patterns. A higher score for meal contents represents a greater preference for 296
a high-fat diet and sweets (e.g., confectioneries and sweet buns). 17 20
A higher score for 297
temporal eating patterns represents a greater irregularity in the timing and number of meals 298
consumed and a later timing of meals. 17 20
Consistent with these changes in obesity-related 299
eating behavior in rotating shift workers, our previous studies have shown that rotating shift 300
workers consumed more confectioneries and sugar-sweetened beverages compared with day 301
workers, 7 and that the rate of skipping breakfast on days on the day shift in rotating shift 302
workers was significantly higher compared with day workers among female nurses 8 in large 303
population studies. Furthermore, the preference for a high-fat diet was confirmed following a 304
simulated night shift. 25
305
306
Chronic positive energy balance is one of the well-known causes of lifestyle-related diseases 307
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which are mediated by obesity. The positive energy balance is caused by the excess dietary 308
intake relative to energy expenditure, and can be relatively easily induced by consuming large 309
portions of food 26
and/or high energy-dense food such as snacks and confectioneries. 27
In our 310
samples, the score for meal contents was significantly and positively associated with BMI 311
(Pearson's correlation = 0.186, p = 0.031). Recently, studies have shown that the timing of 312
meal intake (i .e., skipping breakfast, greater caloric intake at dinner, or later t iming of dinner) 313
also contributed to increases in BMI and the higher risk of obesity, 5 28
after statistically 314
controlling for total energy intake, in individuals who do not engage in night shift work. In 315
our samples, the score for temporal dietary patterns was significantly and positively associated 316
with BMI (Pearson's correlation = 0.281, p = 0.005). Regarding rotating shift workers, it has 317
been found that nocturnal energy intake (00:00–04:00) on days on the night shift was 318
associated with increases in body weight. 29
Another recent study found that the significant 319
effects of rotating shift work on BMI remained after controlling for daily total energy intake 320
and daily physical activity. 7 With regard to the physiological background of these relations, 321
the timing of meals might change the lipid metabolism. 4 30 31
Considered together with 322
higher scores for meal contents and temporal eating patterns in rotating shift workers (Table 2) 323
compared with those scores of day workers and normal-weight women, 32
the timing of meal 324
intake, as well as meal contents, may be an important factor in prevention and improvement of 325
obesity and lifestyle-related diseases in rotating shift workers, and this should be examined in 326
the future. In particular, studies on the effects of the timing of meal intake on days on the 327
night shift on BMI may be needed. 328
329
The means of BMI for day workers and rotating shift workers in our samples were not 330
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significantly different and fell in the normal range of BMI. However, it should be noted that 331
age was significantly higher in day workers, and that years of experience of rotating shift work 332
were significantly longer in day workers compared with rotating shift workers (Table 1). 333
Previous studies have indicated that duration of rotating shift work may have a positive 334
relationship with overweight/obesity 33
and increasing BMI, 7 indicating that there may be 335
accumulative effects of rotating shift work on BMI in day workers (Table.1). In addition, in 336
Japan, more than 20% of women in their 20s are underweight (BMI < 18.5 kg/m2).
34 This 337
percentage is much higher than in most developed countries. 35
Also, in epidemiological 338
studies using a larger sample size, mean BMI scores for rotating shift workers in Japanese 339
female nurses (e.g. Tada et al.; 21.6±3.2 kg/m2, n = 1579
7; Lee et al.; 22.3±3.0 kg/m
2, n = 340
18108 36
) were in the normal range, while this value in other countries was higher than the 341
normal range (e.g. Australian and New Zealand nurses; 26.4±5.3 kg/m2, n = 320
37; Canadian 342
nurses; 25.7±5.1 kg/m2, n = 4111
38). Considered together with the higher percentage of body 343
fat levels, especially at lower BMI, in Japanese compared with Caucasians and American 344
Blacks, 39
Japanese female nurses engaging in rotating shift work should be careful of gains in 345
BMI and/or the percentage of body fat as well as BMI. 346
347
There were several limitations to this study. First, the effect of other rotating shift systems on 348
eating behaviors remains unclear. Morikawa et al. 40
reported that people working on a 349
rotating 2-shift system had a higher risk of increased BMI compared with people working on a 350
rotating 3-shift system, indicating that the type of rotating shift system might affect eating 351
behavior. Second, the current participants were all Japanese female nurses at a particular city 352
hospital. Studies in other populations may be required to clarify to what extent the present 353
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results can be generalized. Finally, potential confounding variables such as psychological 354
stress and sensations of fatigue may not have been fully considered. 355
356
Conclusions 357
In conclusion, rotating shift work was associated with a more unbalanced diet and abnormal 358
temporal eating patterns, and the associations may be mediated and/or modulated partly by 359
being of the Evening type. These findings have important implications for the development 360
of novel strategies for preventing excessive weight gain in rotating shift workers. 361
362
Acknowledgments 363
We thank the chief nurses and staff of each medical ward in Ome City General Hospital, and all 364
persons who cooperated in conducting this study. 365
366
Contributorship statement 367
TY, YK, ON, JO, RT and FT designed the research; TY, AS, YY, AH, and YT conducted the 368
research; TY, YT, and FT analyzed the data; TY, YK, and FT wrote the manuscript; TY had 369
primary responsibility for the final content. All the authors read and approved the final 370
manuscript. 371
372
Competing interests 373
The authors have no competing interests. 374
375
Funding 376
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This study was supported by a grant from the Japan Society for the Promotion of Science 377
(Grant-in-Aid for start-up 26882040). 378
379
Data sharing statement 380
No additional data available. 381
382
383
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STROBE Statement—checklist of items that should be included in reports of observational studies
Item
No Recommendation
Title and
abstract
1 (a) Indicate the study’s design with a commonly used term in the title or the
abstract
Page 1
(b) Provide in the abstract an informative and balanced summary of what was
done and what was found
Page 2
Introduction
Background
/rationale
2 Explain the scientific background and rationale for the investigation being
reported
Page 4-6
Objectives 3 State specific objectives, including any prespecified hypotheses Page 5
Methods
Study
design
4 Present key elements of study design early in the paper Page 8
Setting 5 Describe the setting, locations, and relevant dates, including periods of
recruitment, exposure, follow-up, and data collection
Page 7
Participants 6 (a) Cohort study—Give the eligibility criteria, and the sources and methods of
selection of participants. Describe methods of follow-up
Case-control study—Give the eligibility criteria, and the sources and methods
of case ascertainment and control selection. Give the rationale for the choice of
cases and controls
Cross-sectional study—Give the eligibility criteria, and the sources and
methods of selection of participants
Page 7
(b) Cohort study—For matched studies, give matching criteria and number of
exposed and unexposed
Case-control study—For matched studies, give matching criteria and the
number of controls per case
-
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and
effect modifiers. Give diagnostic criteria, if applicable
Page 8
Data
sources/
measuremen
t
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
Page 8
Bias 9 Describe any efforts to address potential sources of bias Page 9
Study size 10 Explain how the study size was arrived at Page 7
Quantitative
variables
11 Explain how quantitative variables were handled in the analyses. If applicable,
describe which groupings were chosen and why
Page 9
Statistical
methods
12 (a) Describe all statistical methods, including those used to control for
confounding
Page 9
(b) Describe any methods used to examine subgroups and interactions -
(c) Explain how missing data were addressed Page 7
(d) Cohort study—If applicable, explain how loss to follow-up was addressed
Case-control study—If applicable, explain how matching of cases and controls
was addressed
Cross-sectional study—If applicable, describe analytical methods taking
account of sampling strategy
Page 9
(e) Describe any sensitivity analyses -
Continued on next page
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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
Table 1, Page 10
(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
Table 1, Page 10
(b) Indicate number of participants with missing data for each variable of
interest
Table 1, Page 10
(c) Cohort study—Summarise follow-up time (eg, average and total amount) -
Outcome
data
15* Cohort study—Report numbers of outcome events or summary measures over
time
-
Case-control study—Report numbers in each exposure category, or summary
measures of exposure
-
Cross-sectional study—Report numbers of outcome events or summary
measures
Table 1, Page 10
Table 2, Page 11
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
Table 3, Page 13
(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
-
Discussion
Key results 18 Summarise key results with reference to study objectives Page 15
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
Page 18
Interpretation 20 Give a cautious overall interpretation of results considering objectives,
limitations, multiplicity of analyses, results from similar studies, and other
relevant evidence
Page 18
Generalisability 21 Discuss the generalisability (external validity) of the study results Page 18
Other information
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
Page 19
*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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Association of eating behaviors with diurnal preference and rotating shift work in Japanese female nurses: a cross-
sectional study
Journal: BMJ Open
Manuscript ID bmjopen-2016-011987.R1
Article Type: Research
Date Submitted by the Author: 12-Jul-2016
Complete List of Authors: Yoshizaki, Takahiro; Toyo University, Faculty of Food and Nutritional Sciences Kawano, Yukari; Tokyo University of Agriculture, Department of Nutritional
Science, Faculty of Applied Bio-Science Noguchi, Osamu; Ome City General Hospital, Department of Gastroenterology Onishi, Junko; Ome City General Hospital, Department of Nursing Teramoto, Reiko; Ome City General Hospital, Department of Clinical Nutrition Sunami, Ayaka; Tokyo University of Agriculture, Graduate School of Agriculture Yokoyama, Yuri; Tokyo University of Agriculture, Graduate School of Agriculture Tada, Yuki; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science
Hida, Azumi; Tokyo University of Agriculture, Department of Nutritional Science, Faculty of Applied Bio-Science Togo, Fumiharu; The University of Tokyo, Graduate School of Education
<b>Primary Subject Heading</b>:
Nutrition and metabolism
Secondary Subject Heading: Epidemiology, Occupational and environmental medicine, Public health
Keywords: Dietary habits, Chronotype, Rotating shift worker, Diurnal preference
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1
Association of eating behaviors with diurnal preference and 1
rotating shift work in Japanese female nurses: a 2
cross-sectional study 3
4
Takahiro Yoshizaki1, Yukari Kawano
2, Osamu Noguchi
3, Junko Onishi
4, Reiko Teramoto
5, 5
Ayaka Sunami6, Yuri Yokoyama
6, Yuki Tada
2, Azumi Hida
2, Fumiharu Togo
7 6
7
1Faculty of Food and Nutritional Sciences, Toyo University, Gunma, Japan 8
2Department of Nutritional Science, Faculty of Applied Bio-Science, Tokyo University of 9
Agriculture, Tokyo, Japan 10
3Department of Gastroenterology, Ome City General Hospital, Tokyo, Japan 11
4Department of Nursing, Ome City General Hospital, Tokyo, Japan 12
5Department of Clinical Nutrition, Ome City General Hospital, Tokyo, Japan 13
6Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan 14
7Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo, 15
Tokyo, Japan 16
17
Running head: Rotating Shift Work and Eating Behaviors 18
Address correspondence to: 19
Takahiro Yoshizaki, Ph.D. 20
Faculty of Food and Nutritional Sciences, Toyo University 21
1-1-1 Izumino, Oura-gun, Itakura-machi, Gunma 374-0193, Japan 22
Tel: +81-276-82-9012 Fax: +81-276-82-9000 E-mail: [email protected] 23
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ABSTRACT 24
Objectives 25
Our study examines differences in eating behavior between day workers and rotating shift 26
workers, and considers whether diurnal preference could explain the differences. 27
Methods 28
Japanese female nurses were studied (39 day workers and 123 rotating shift workers, aged 21–29
63) using self-administered questionnaires. The questionnaires assessed eating behaviors, 30
diurnal preference, and demographic characteristics. The questionnaire in the Guidelines for 31
the management of obesity disease issued by the Japan Society for the Study of Obesity was 32
used to obtain scores for the levels of obesity-related eating behaviors, including cognition of 33
constitution, motivation for eating, eating as a diversion, feeling of satiety, eating style, meal 34
contents and temporal eating patterns. The Japanese version of the Morningness-Eveningness 35
(ME) questionnaire was used to measure self-rated preference for the degree to which people 36
prefer to be active in the morning or the evening (morningness-eveningness). 37
Results 38
The scores for meal contents and temporal eating patterns in rotating shift workers were 39
significantly higher than those in day workers. The ME score of rotating shift workers was 40
significantly lower, indicating greater eveningness/less morningness among rotating shift 41
workers. Multivariate linear regression revealed that the ME score was significantly 42
negatively associated with temporal eating patterns and showed a negative association with the 43
score for meal contents at a trend level, while current work shift was not significantly 44
correlated with the scores. 45
Conclusions 46
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These results suggest that eating behaviors for rotating shift workers are associated with a 47
more unbalanced diet and abnormal temporal eating patterns and that the associations may be 48
explained by diurnal preference rather than by rotating shift work. 49
50
Keywords: Dietary habits; Chronotype; Rotating shift worker 51
52
STRENGTHS and LIMITATIONS of THIS STUDY 53
・There are few studies that have clarified whether the difference of diurnal preference explains 54
changes in eating behaviors in rotating shift workers. 55
・The aim of the present study was to elucidate the differences in obesity-related eating 56
behavior between day workers and rotating shift workers, considering the diurnal preference, 57
among Japanese female nurses. 58
・Eating behaviors for rotating shift workers were associated with more unbalanced diets and 59
more abnormal temporal eating patterns, which may be explained by the diurnal preference 60
rather than by rotating shift work. 61
・These findings have important implications for the development of novel strategies for 62
preventing excessive weight gain in rotating shift workers. 63
・Variables, such as eating behaviors and diurnal preference, were self-reported. Continuous 64
monitoring of dietary intake and the sleep–wake cycle may be needed in future research. 65
66
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1. INTRODUCTION 67
The growth in the proportion of the population aged 65 years old and over leads to an increase 68
in the social demand for nurses in medical facilities. Among them, health problems can be 69
caused by severe working conditions such as shifting of work schedules between the day and 70
night (i.e., rotating shift work). Previous studies have suggested that rotating shift work is 71
related to higher r isks of health problems, including obesity, increases in body mass index 72
(BMI), and adiposity with abnormal metabolism, compared with fixed day work. 1-3
One of the 73
possible factors for increasing the risks of these health problems in rotating shift workers is 74
their altered eating behavior. 4 5
Our previous studies demonstrated that female workers who 75
engaged in rotating shift work consumed more sugar-sweetened beverages and snacks than day 76
workers, 6 7
and that the rate of subjects who reported skipping breakfast almost everyday (80–77
100%) on days on the day shift was significantly higher in rotating shift workers compared 78
with day workers. 8 Recent studies by other groups have also showed that rotating shift workers 79
had irregular meal times (e.g., skipping meals or midnight snacks), 9 and unbalanced dietary 80
intake (e.g., greater intake of fats and oils and lower intake of vegetables) when compared with 81
day workers. 10
However, it is unclear which aspects of obesity-related eating behavior change 82
in rotating shift workers, and which factors contribute to the altered eating behaviors in 83
rotating shift workers. 84
85
One plausible mechanism contributing to the altered eating behaviors in rotating shift workers 86
is a disturbed circadian rhythm. Our previous study revealed that rotating shift workers had a 87
significant phase delay in the 24-h rhythm of cardiac autonomic nervous system activity 88
compared with fixed day workers, 11
suggesting a phase delay of the circadian rhythm among 89
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rotating shift workers. The endogenous circadian clocks, controlled by the master circadian 90
clock in the suprachiasmatic nuclei of the hypothalamus, play a significant role in regulating a 91
number of circadian and daily physiological rhythms, including feeding behavior. 12
For 92
example, a human laboratory study showed that the circadian clock regulated hunger and 93
appetite independently of the fasting-feeding rhythm and the sleep-wake cycle, 13
indicating 94
that the phase delay of the circadian clock might modify the timing of eating. Moreover, a 95
recent study revealed that a late midpoint of nocturnal sleep was associated with increases in 96
energy intake from undesirable dietary contents such as alcoholic beverages, confectioneries, 97
fats and oils, and meats in individuals who did not engage in night shift work. 14
Despite these 98
available data, which suggest a possibility of a close association between eating behavior and 99
the circadian clock, there are few studies that have clarified whether the association explains 100
changes in eating behaviors in rotating shift workers. 101
102
To investigate epidemiologically the phase of the circadian clock during daily life, individual 103
preference in the phase of the sleep-wake cycle (i.e. , diurnal preference, 104
morningness-eveningness, or chronotype), which may be different from the actual sleep-wake 105
cycle during daily life, was assessed using the Japanese version of the 106
Morningness-Eveningness questionnaire by Torsvall and Akerstedt. 15 -18
Diurnal preference 107
(e.g., evening type or morning type) are attributed to differences in the phase of the circadian 108
clock. 19
Therefore, the aim of the present study was to elucidate the association between 109
rotating shift work and obesity-related eating behaviors, considering the diurnal preference, 110
among Japanese female nurses. Eating behaviors were investigated using the questionnaire in 111
the Guidelines for the management of obesity disease issued by the Japan Society for the Study 112
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of Obesity. 20 21
Characteristics of eating behavior which were different between overweight 113
and normal weight individuals were extracted from an interview survey and compiled to 114
produce the questionnaire. 22
Our hypothesis was that rotating shift workers would have 115
obesity-related eating behaviors associated with meal contents (e.g., greater intake of specific 116
nutrients) and temporal eating patterns (e.g., skipping breakfast and/or late dinner), and that 117
diurnal preference would partially explain the differences in obesity-related eating behaviors 118
between day workers and rotating shift workers. 119
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2. METHODS 120
2.1 Participants 121
The study population consisted of nurses working at a general hospital in the center of Ome 122
city. Ome city is located in the west side of the Tokyo metropolitan area and is the fifth 123
largest city in the metropolis. Urbanization and industrialization are present in the region of 124
the plain, while districts in the hilly area in the western region of the city have rural 125
populations. A total of 506 nurses were handed the questionnaires by the chief nursing officer 126
on each ward. The purpose of this study and data handling procedures were described in a 127
cover letter with the questionnaire. Agreement to participate in this study was assumed on the 128
basis of receipt of an anonymous questionnaire. A total of 218 nurses (43.1%; age 19–63 yr) 129
responded. Among them, 56 were excluded from the analysis because of missing data [age 130
(n=2), current work schedules (n=6), residential status (n=1), marital status (n=2), years of 131
experience as a rotating shift worker (n=23), smoking status (n=2), alcohol status (n=4), 132
number of night shifts during the previous month (n=6), and the questionnaire about diurnal 133
preference (n=13)]. Because the scoring method for the questionnaire about obesity-related 134
eating behavior was different for men and women, 23 24
we decided to exclude the small number 135
of data from male nurses (n=20). As a result, 162 female nurses (39 day workers and 123 136
shift workers) were analyzed (Figure 1). Their mean total duration of experience in their 137
current job was 12.2 ± 10.3 [SD] yr. In this study, individuals who worked fixed day shifts 138
only (i.e. 08:30–17:15 h) were defined as “day workers”, while those who worked in either a 139
two-shift system (days and nights, at 08:30–17:15 and 16:30–09:15 h) or a forward-rotating 140
three-shift system (days, evenings and nights, at 08:30–17:15, 16:30–01:00 and 00:45–09:15, 141
respectively) were classified as “rotating shift workers”. The mean number of night shifts 142
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was 7.6 ± 3.1 during the previous month. All the study procedures were reviewed and 143
approved by the Ethics Committee at the Tokyo University of Agriculture (No. 1111). 144
145
2.2 Assessments 146
A cross-sectional study using self-administered questionnaires on demographic characteristics, 147
diurnal preference and eating behavior was conducted in the general hospital at the beginning 148
of September 2012. Completed questionnaires were returned within two weeks. 149
Demographic characteristics of the participants included in the questionnaire were the 150
following: age, height, weight, current work schedule, years of experience in the current job 151
and as a rotating shift worker, marital status, residential status, smoking status, alcohol status, 152
and the number of night shifts during the previous month. Body mass index (BMI) was 153
calculated on the basis of self-reported height and weight [weight / height2 (kg / m
2)]. The 154
Japanese version of the Morningness-Eveningness questionnaire by Torsvall and Akerstedt was 155
used to measure self-rated preference for activity in the morning or the evening 156
(morningness-eveningness). 15 17 18
Based on seven items about daily sleep habits or preference 157
consisting of 0–3 Likert scales, the Morningness-Eveningness score (ME score) was calculated 158
(range: 7–28 points). A lower ME score indicates a tendency for a greater preference for 159
activity in the evening (evening type), while a higher ME score indicates a greater preference 160
for activity in the morning (morning type). We calculated the internal consistency for the 161
Morningness–Eveningness questionnaire using the present data, which revealed a Cronbach’s 162
alpha of 0.73. Data about habitual eating behaviors during the previous month were obtained 163
from the response to the eating behavior questionnaire issued by the Japan Society for the 164
Study of Obesity, 20 21
which was developed to detect obesity-related eating behavior. The 165
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details of the contents of the questionnaire have been shown in previous studies. 22 23 25 26
In 166
brief, each of the 55 items on eating habits is rated on a four-point scale ranging from “strongly 167
disagree” to “strongly agree”. These items form seven separate scales: cognition of 168
constitution (range: 6–24), motivation for eating (range: 9–36), eating as a diversion (range: 4–169
16), feeling of satiety (range: 6–24), eating style (range: 5–20), meal contents (range: 7–28), 170
and temporal eating patterns (range: 8–32). Higher scores indicate more improper eating 171
behavior in terms of a higher probability of obesity. 22 23
We also calculated the internal 172
consistency using the data in this study, with Cronbach’s alpha found to be 0.62 for cognition 173
of constitution, 0.82 for motivation for eating, 0.71 for eating as diversion, 0.63 for feeling of 174
satiety, 0.82 for eating style, 0.77 for meal contents and 0.71 for temporal eating patterns. 175
176
2.3 Statistical analysis 177
After the normal distr ibution of variables had been tested by Kolmogorov-Smirnov test, the 178
t-test or Mann–Whitney U test and the χ2 test or Fisher 's exact test were used for continuous 179
and categorical variables, respectively, to compare the difference in demographic 180
characteristics, the ME score, and the scores for eating behavior between day workers and 181
rotating shift workers. For categorical variables, residuals between the observed and 182
expected frequencies were standardized to determine cells which were statistically different 183
from expected values. Effect sizes for the difference in the scores of eating behavior between 184
the groups were assessed using Cohen’s d. Simple and multivariate linear regression (model 185
1) were performed with each score for eating behavior (meal contents or temporal eating 186
patterns) as dependent variables, and current work schedule (0 = day work, 1 = rotating shift 187
work) and the ME score (continuous, in points) as independent variables. The model was 188
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extended (model 2) using an interaction term (shift work × ME score) with the following 189
demographic characteristics for covariate adjustment: age (continuous, in years), years of 190
experience as a rotating shift worker (continuous, in years), marital status (0 = married, 1 = 191
unmarried or divorced), residential status (0 = living alone, 1 = not living alone), smoking 192
status (‘Do you smoke?’; 0 = no, 1 = yes), alcohol status (‘Do you drink alcohol?’; 0 = no, 1 = 193
yes) and the number of night shifts during the previous month (continuous, in days). All 194
statistical analyses were performed with an SPSS statistical software package (IBM SPSS 22.0 195
for Windows, SPSS Japan). P values less than 0.05 were considered statistically significant 196
using two-tailed tests. 197
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3. RESULTS 198
The demographic characteristics of day workers and rotating shift workers are shown in Table 199
1. Age was significantly higher in day workers compared with rotating shift workers (p < 200
0.05). The years of experience in the current work schedule were significantly more in day 201
workers compared with rotating shift workers (p < 0.05). Marital status and residential status 202
were significantly associated with the current work schedule (p < 0.05). The ME score for 203
rotating shift workers was significantly lower compared with day workers (p < 0.05), 204
indicating greater eveningness/less morningness among rotating shift workers compared with 205
day workers. This significant difference was not attenuated after controlling for age as a 206
confounding variable (data not shown). 207
208
Table 1 Demographic characteristics of day workers and rotating 209
shift workers 210
Day workers Shift workers
P values
n=39 n=123
Age† (years) 44.2 ± 10.9 34.7 ± 8.7 < 0.001
Height†a
(cm) 156.7 ± 5.6 157.5 ± 5.5 0.175
Weight†b
(kg) 53.4 ± 8.3 53.8 ± 8.9 0.784
BMI†c
(kg/m2) 21.7 ± 2.7 21.7 ± 3.5 0.676
ME score†§
(points) 20.8 ± 3.3 17.1 ± 4.0 < 0.001
Years of experience
Current work† (years) 17.4 ± 12.0 10.6 ± 9.2 0.002
Rotating shift work† (years) 11.8 ± 10.7 9.7 ± 8.7 0.652
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Number of night shifts (day/month) 0.0 ± 0.0 7.6 ± 3.1 -
Marital status‡ Married 32 ( 82 )
* 50 ( 41 )
0.001
Unmarried or divorced 7 ( 18 ) 73 ( 59 ) *
Residential status‡ Living alone 3 ( 8 ) 33 ( 27 )
*
0.014
Not living alone 36 ( 92 ) * 90 ( 73 )
Smoking status Yes 4 ( 10 ) 17 ( 14 )
0.785
No 35 ( 90 ) 106 ( 86 )
Alcohol status‡ Yes 21 ( 54 ) 51 ( 41 )
0.198
No 18 ( 46 ) 72 ( 59 )
211
Values are means ± standard deviation or number (%). 212
BMI, body mass index; ME score, Morningness-Eveningness score 213 †Mann-Whitney U test 214
‡χ
2 test or Fisher's exact test (When p < 0.05, standardized residuals were determined for each 215
cell.) 216 *p < 0.05 217
§A lower ME score is indicative of the evening type. 218
aShift workers, n=120
219
bShift workers, n=118
220
cShift workers, n=118
221
222
Scores for the obesity-related eating behaviors of day workers and rotating shift workers are 223
shown in Table 2. The scores for meal contents and temporal eating patterns significantly 224
differed between the groups (p < 0.05), indicating an unbalanced diet and more irregular timing 225
of meals among rotating shift workers compared with day workers. Scores for other eating 226
behaviors did not differ between the groups (p > 0.05). 227
228
229
Table 2 Scores for habitual eating behavior in day workers and 230
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rotating shift workers 231
Normal Day workers Shift workers
Cohen’s d p values
(Ref. 23) n=39 n=123
Cognition of constitution†a
(points) 14 14.3 ± 3.4 13.6 ± 3.7 –0.19 0.328
Motivation for eating‡b
(points) 18 19.5 ± 4.9 18.8 ± 5.6 –0.13 0.384
Eating as a diversion‡c
(points) 7 7.4 ± 2.4 7.1 ± 2.9 –0.11 0.310
Feeling of satiety‡ (points) 10 10.9 ± 3.1 11.3 ± 3.2 0.13 0.427
Eating style‡ (points) 9 9.8 ± 3.5 9.7 ± 3.6 –0.03 0.629
Meal contents‡ (points) 12 13.9 ± 3.9 15.6 ± 4.5 0.39 0.045
Temporal eating patterns‡d
(points) 16 16.5 ± 4.5 19.5 ± 4.8 0.63 0.001
232
Values are means ± standard deviation. 233
Higher scores indicate more improper eating behavior in terms of a higher probability of 234
obesity: Cognition of weight and constitution, having false recognition of and assumptions 235
about reasons for weight gain; Motivation for eating, having behavioral factors which can 236
induce over-eating; Eating as a diversion, being subject to psychological factors which increase 237
appetite (i.e., perceived mental stress); Feeling of satiety, being prone to have an appetite and 238
to eat as much as possible; Eating style, being prone to eat fast; Meal contents, having a 239
preference for a high fat diet and sweets (e.g., confectioneries and sweet buns); Temporal 240
eating patterns, irregularity of timing and number of meals taken during the day and delay in 241
timing of meals. 242 †t-test 243
‡Mann-Whitney U test 244
aShift workers, n=122
245
bShift workers, n=122
246
cDay workers, n=38
247
dShift workers, n=119
248
249
We examined the relationship between rotating shift work, the ME score, and scores for meal 250
contents and temporal eating patterns using simple and multivariate linear regression. Simple 251
linear regression (Table 3, Figure 2) showed that rotating shift work and a lower ME score were 252
significantly (p < 0.05) associated with higher scores for meal contents and temporal eating 253
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patterns. Multivariate linear regression (model 1) showed that the ME score was significantly 254
(p < 0.05) associated with the score for meal contents, while the effect of rotating shift work 255
was not (p = 0.245). Regarding temporal eating patterns, the ME score was significantly 256
associated with the score (p < 0.05), while rotating shift work was attenuated to a trend level 257
only (p = 0.060). In model 2, in which the variables of demographic characteristics which 258
significantly (p < 0.05) differed between the groups (i.e., age, years of experience as a rotating 259
shift worker, marital status, residential status, and number of night shifts during the previous 260
month) and smoking and alcohol status were controlled, the correlations with the ME score 261
decreased slightly but remained significantly negative (β = –0. 338, p < 0.05) for temporal 262
eating patterns or at a trend level (β = –0.196, p = 0.051) for meal contents, while there were 263
no significant interactions between shift work and the ME score with the scores for meal 264
contents and temporal eating patterns. 265
266
Table 3 Association of current shift schedule (rotating shift work) 267
and diurnal preference with scores for meal contents and temporal 268
eating patterns in multivariate linear regression models 269
Independent
variables
Unstandardized
coefficients
Standardized
coefficients p values
B SE β
Meal contents
Crude
Rotating shift work 1.689 0.804 0.164 0.037
ME score –0.223 0.082 –0.210 0.007
Model 1
Rotating shift work 1.007 0.862 0.098 0.245
ME score –0.183 0.089 –0.172 0.041
Model 2a
Rotating shift work 1.486 1.441 0.144 0.304
ME score –0.208 0.106 –0.196 0.051
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Shift work × ME score 0.222 0.247 0.100 0.371
Temporal eating patterns
Crude
Rotating shift work 3.211 0.867 0.284 < 0.001
ME score –0.465 0.086 –0.397 < 0.001
Model 1
Rotating shift work 1.698 0.897 0.150 0.060
ME score –0.395 0.093 –0.338 < 0.001
Model 2a
Rotating shift work 1.426 1.500 0.126 0.342
ME score –0.395 0.110 –0.338 < 0.001
Shift work × ME score –0.061 0.255 –0.025 0.811 270 aAdjusted by age, years of experience as a rotating shift worker, marital status, residential 271
status, smoking status, alcohol status, and number of night shifts during the previous month. 272
Years of experience in the current work schedule were not included in Model 2 because of a 273
high level of multicollinearity (Variance inflation factor = 8.101). 274
275
276
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4. DISCUSSION 277
Our cross-sectional study explored the differences in obesity-related eating behavior between 278
day workers and rotating shift workers, considering diurnal preference, among Japanese female 279
nurses. Scores for meal contents and temporal eating patterns were significantly higher in 280
rotating shift workers than in day workers (p < 0.05). The ME score of rotating shift workers 281
was significantly (p < 0.05) lower compared with day workers, indicating greater 282
eveningness/less morningness among rotating shift workers. Multivariate linear regression 283
revealed that the correlation with the ME score was significantly negative (β = –0.338, p < 284
0.05) for the score for temporal eating patterns and showed a negative association with the 285
score for meal contents at a trend level (β = –0.196, p = 0.051), while current work shift (i.e., 286
rotating shift work) was not significantly correlated with the scores. These results suggest 287
that eating behaviors for rotating shift workers are associated with a more unbalanced diet and 288
abnormal temporal eating patterns and that the associations could be explained by diurnal 289
preference (e.g., greater eveningness/less morningness) rather than by rotating shift work. To 290
the best of our knowledge, this is the first study to show the associations between rotating shift 291
work, diurnal preference, and eating behavior. 292
293
Given the fact that the evening type closely correlates with delays in the phase angle of the 294
circadian rhythm 19
and that the phase delay can be caused by light exposure and sleep/dark 295
schedules during nights on the days of the night shift, 27
our study indicates that being of 296
greater eveningness/less morningness, or the phase delay of the circadian rhythm, may 297
correlate with altered eating behavior in rotating shift workers. This indication is supported 298
by previous studies. 11 28
For example, one previous study revealed that rotating shift workers 299
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showed a phase delay in the circadian rhythm compared with day workers. 11
In addition, 300
rotating shift workers have a tendency for more evening types compared with day workers, 8 29
301
which is consistent with our results. We also demonstrated that a greater phase delay of the 302
circadian rhythm was associated with a later timing of breakfast among rotating shift workers. 303
28 However, causality between diurnal preference or phase angle of the circadian rhythm and 304
altered eating behavior could not be examined, although these may have interactive effects. I t 305
should be explored in future studies whether changes from the evening type to the morning 306
type in diurnal preference or the phase advance of the circadian rhythm would improve eating 307
behavior in rotating shift workers. 308
309
Our results show that rotating shift work is associated with higher scores for meal contents and 310
temporal eating patterns. A higher score for meal contents represents a greater preference for 311
a high-fat diet and sweets (e.g., confectioneries and sweet buns). 21 23 25
A higher score for 312
temporal eating patterns represents a greater irregularity in the timing and number of meals 313
consumed and a later timing of meals. 21 23
Consistent with these changes in obesity-related 314
eating behavior in rotating shift workers, our previous studies have shown that rotating shift 315
workers consumed more confectioneries and sugar-sweetened beverages compared with day 316
workers, 7 and that the rate of skipping breakfast on days on the day shift in rotating shift 317
workers was significantly higher compared with day workers among female nurses 8 in large 318
population studies. Furthermore, the preference for a high-fat diet was confirmed following a 319
simulated night shift. 30
320
321
Chronic positive energy balance is one of the well-known causes of lifestyle-related diseases 322
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which are mediated by obesity. The positive energy balance is caused by the excess dietary 323
intake relative to energy expenditure, and can be relatively easily induced by consuming large 324
portions of food 31
and/or high energy-dense food such as snacks and confectioneries. 32
In our 325
samples, the score for meal contents was significantly and positively associated with BMI 326
(Pearson's correlation = 0.186, p = 0.031). Recently, studies have shown that the timing of 327
meal intake (i .e., skipping breakfast, greater caloric intake at dinner, or later t iming of dinner) 328
also contributed to increases in BMI and the higher risk of obesity, 5 33
after statistically 329
controlling for total energy intake, in individuals who do not engage in night shift work. In 330
our samples, the score for temporal dietary patterns was significantly and positively associated 331
with BMI (Pearson's correlation = 0.281, p = 0.005). Regarding rotating shift workers, it has 332
been found that nocturnal energy intake (00:00–04:00) on days on the night shift was 333
associated with increases in body weight. 34
Another recent study found that the significant 334
effects of rotating shift work on BMI remained after controlling for daily total energy intake 335
and daily physical activity. 7 With regard to the physiological background of these relations, 336
the timing of meals might change the lipid metabolism. 4 35 36
Considered together with higher 337
scores for meal contents and temporal eating patterns in rotating shift workers (Table 2) 338
compared with those scores of day workers and normal-weight women, 23
the timing of meal 339
intake, as well as meal contents, may be an important factor in prevention and improvement of 340
obesity and lifestyle-related diseases in rotating shift workers, and this should be examined in 341
the future. In particular, studies on the effects of the timing of meal intake on days on the 342
night shift on BMI may be needed. 343
344
The means of BMI for day workers and rotating shift workers in our samples were not 345
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significantly different and fell in the normal range of BMI. However, it should be noted that 346
age was significantly higher in day workers, and that years of experience of rotating shift work 347
were significantly longer in day workers compared with rotating shift workers (Table 1). 348
Previous studies have indicated that duration of rotating shift work may have a positive 349
relationship with overweight/obesity 37
and increasing BMI, 7 indicating that there may be 350
accumulative effects of rotating shift work on BMI in day workers (Table.1). In addition, in 351
Japan, more than 20% of women in their 20s are underweight (BMI < 18.5 kg/m2).
38 This 352
percentage is much higher than in most developed countries. 39
Also, in epidemiological 353
studies using a larger sample size, mean BMI scores for rotating shift workers in Japanese 354
female nurses (e.g., Tada et al.; 21.6±3.2 kg/m2, n = 1579
7; Lee et al. ; 22.3±3.0 kg/m
2, n = 355
18108 40
) were in the normal range, while this value in other countries was higher than the 356
normal range (e.g., Australian and New Zealand nurses; 26.4±5.3 kg/m2, n = 320
41; Canadian 357
nurses; 25.7±5.1 kg/m2, n = 4111
42). Considered together with the higher percentage of body 358
fat levels, especially at lower BMI, in Japanese compared with Caucasians and American 359
Blacks, 43
Japanese female nurses engaging in rotating shift work should be careful of gains in 360
BMI and/or the percentage of body fat as well as BMI. 361
362
There were several limitations to this study. First, variables, such as eating behaviors and 363
diurnal preference, were self-reported. Continuous monitoring of dietary intake and the 364
sleep–wake cycle may be needed in future research. Second, the effect of other rotating shift 365
systems on eating behaviors remains unclear. Morikawa et al 44
reported that people working 366
on a rotating two-shift system had a higher risk of increased BMI compared with people 367
working on a rotating three-shift system, indicating that the type of rotating shift system might 368
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affect eating behavior. Third, the current participants were all Japanese female nurses at a 369
particular city hospital. Studies in other populations may be required to clarify to what extent 370
the present results can be generalized. Fourth, the unbalanced sample size between day and 371
shift workers may have contributed to a decrease in the statistical power to detect significant 372
differences in dietary behaviors between the groups, even though we could not detect 373
differences of a negligible effect size (absolute Cohen’s d < 0.15) or a lower range of a small 374
effect size (0.15 ≤ absolute Cohen’s d < 0.02) using statistical tests. Finally, potential 375
confounding variables, such as habitual sleep duration, daily variation in sleep timing, 376
psychological stress and sensations of fatigue, may not have been fully considered. 377
378
Conclusions 379
In conclusion, eating behaviors for rotating shift workers were associated with more 380
unbalanced diets and more abnormal temporal eating patterns, which may be explained by the 381
diurnal preference rather than by rotating shift work. These findings have important 382
implications for the development of novel strategies for preventing excessive weight gain in 383
rotating shift workers. 384
385
Acknowledgments 386
We thank the chief nurses and staff of each medical ward in Ome City General Hospital, and all 387
persons who cooperated in conducting this study. 388
389
Contributorship statement 390
TY, YK, ON, JO, RT and FT designed the research; TY, AS, YY, AH, and YT conducted the 391
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research; TY, YT, and FT analyzed the data; TY, YK, and FT wrote the manuscript; TY had 392
primary responsibility for the final content. All the authors read and approved the final 393
manuscript. 394
395
Competing interests 396
The authors have no competing interests. 397
398
Funding 399
This study was supported by a grant from the Japan Society for the Promotion of Science 400
(Grant-in-Aid for start-up 26882040). 401
402
Data sharing statement 403
No additional data available. 404
405
406
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Figure legends 519
Figure 1 Flowchart of study participants. 520
521
Figure 2 The relationship between the Morningness-Eveningness score 522
and the meal contents and temporal eating patterns scores. 523
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Figure 1 Flowchart of study participants.
190x142mm (300 x 300 DPI)
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Figure 2 The relationship between the Morningness-Eveningness score and the meal contents and temporal
eating patterns scores.
201x140mm (300 x 300 DPI)
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STROBE Statement—checklist of items that should be included in reports of observational studies
Item
No Recommendation
Title and
abstract
1 (a) Indicate the study’s design with a commonly used term in the title or the
abstract
Page 1
(b) Provide in the abstract an informative and balanced summary of what was
done and what was found
Page 2
Introduction
Background
/rationale
2 Explain the scientific background and rationale for the investigation being
reported
Page 4-6
Objectives 3 State specific objectives, including any prespecified hypotheses Page 5
Methods
Study
design
4 Present key elements of study design early in the paper Page 8
Setting 5 Describe the setting, locations, and relevant dates, including periods of
recruitment, exposure, follow-up, and data collection
Page 7
Participants 6 (a) Cohort study—Give the eligibility criteria, and the sources and methods of
selection of participants. Describe methods of follow-up
Case-control study—Give the eligibility criteria, and the sources and methods
of case ascertainment and control selection. Give the rationale for the choice of
cases and controls
Cross-sectional study—Give the eligibility criteria, and the sources and
methods of selection of participants
Page 7
(b) Cohort study—For matched studies, give matching criteria and number of
exposed and unexposed
Case-control study—For matched studies, give matching criteria and the
number of controls per case
-
Variables 7 Clearly define all outcomes, exposures, predictors, potential confounders, and
effect modifiers. Give diagnostic criteria, if applicable
Page 8
Data
sources/
measuremen
t
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
Page 8
Bias 9 Describe any efforts to address potential sources of bias Page 9
Study size 10 Explain how the study size was arrived at Page 7
Quantitative
variables
11 Explain how quantitative variables were handled in the analyses. If applicable,
describe which groupings were chosen and why
Page 9
Statistical
methods
12 (a) Describe all statistical methods, including those used to control for
confounding
Page 9
(b) Describe any methods used to examine subgroups and interactions -
(c) Explain how missing data were addressed Page 7
(d) Cohort study—If applicable, explain how loss to follow-up was addressed
Case-control study—If applicable, explain how matching of cases and controls
was addressed
Cross-sectional study—If applicable, describe analytical methods taking
account of sampling strategy
Page 9
(e) Describe any sensitivity analyses -
Continued on next page
Page 30 of 31
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2
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
Table 1, Page 10
(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
Table 1, Page 10
(b) Indicate number of participants with missing data for each variable of
interest
Table 1, Page 10
(c) Cohort study—Summarise follow-up time (eg, average and total amount) -
Outcome
data
15* Cohort study—Report numbers of outcome events or summary measures over
time
-
Case-control study—Report numbers in each exposure category, or summary
measures of exposure
-
Cross-sectional study—Report numbers of outcome events or summary
measures
Table 1, Page 10
Table 2, Page 11
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
Table 3, Page 13
(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
-
Discussion
Key results 18 Summarise key results with reference to study objectives Page 15
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
Page 18
Interpretation 20 Give a cautious overall interpretation of results considering objectives,
limitations, multiplicity of analyses, results from similar studies, and other
relevant evidence
Page 18
Generalisability 21 Discuss the generalisability (external validity) of the study results Page 18
Other information
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
Page 19
*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.
Page 31 of 31
For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml
BMJ Open
123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960
on August 28, 2020 by guest. P
rotected by copyright.http://bm
jopen.bmj.com
/B
MJ O
pen: first published as 10.1136/bmjopen-2016-011987 on 28 N
ovember 2016. D
ownloaded from