Shift Work By M.H.Davari M.D

What is shift work?What is shift work?

Shift work is defined as work outside ofthe normal daylight hours from about 7am

until 6 pm

Shift work is defined as work outside ofthe normal daylight hours from about 7am

until 6 pm

Midnight MidnightNoon

What is Shift Work?

One speaks of shift work if two or more

persons , or teams of persons , work in

sequence at the same work place.

Often , each worker s shift repeats, in same

pattern , over a number of days.

Production process > 8 hours or

continuous

Expensive machinery that must be used

continuously to be profitable

7

How many workers work shift work in North America?

13 – 16% of total work force work some shift workTotal of shift workers estimated to be 24 -25 million

• 5-6 % work evening shifts

• 4-5% work permanent night shift

• 4-5 % work rotating shifts

Why can shift work be difficult?

That is, they are biologically programmed to sleep during the day and be awake at night. e.g. owls,

bats, raccoons

Some animals are what scientists call

NOCTURNAL

DIURNALHumans are what

scientists call

That is, we are biologically programmed to sleep at night and be awake during the day.

How does the body work

Internal Biological Clock (Circadian rhythm)

External stimulants

Circadian Rhythm

• Different body functions vary during the 24 hour day

• Metabolism is greatest in the afternoon to evening

• Most people most alert 10 PM-8 AM and most sleepy 2-4 AM

• The body has a natural cycle of 25 hours• External factors synchronize us to a 24 hour day• The internal clock is located in the

suprachiasmatic hypothalmus

The Suprachiasmatic Nucleus

Circadian body rhythms

• Hormone and gastric secretions• Body tempreture• Bronchial reactivity• Blood Pressure• Sexual arousal• Anxiety• Metabolic Rate• Short term memory• Work performance

Biochemistry and

Circadian Rhythms

External clues “Zeitgebers”

• Light/Dark cycle• Timing of meals• Social interactions• Actual time clock

In 1879 Thomas Edison invented the light bulb.

In 1879 Thomas Edison invented the light bulb.

This forever changed our ability to work at night, but not our biological programming

to sleep at night.

This forever changed our ability to work at night, but not our biological programming

to sleep at night.

The 4 Hazards of Shiftwork

1. Increased risk of errors & accidents in the work and out of the work

2 Insufficient daytime sleep leads to increased fatigue & sleepiness

3. Increase in health problems

4. Increase in social and domestic problems

• Fatigue affects alertness in many shiftworkers

• 80-90 % of shiftworkers feel sleepy during night shift (?% nap!)

• Studies show increase in accident rate

• Tendency for more severe / serious accidents to occur

Alertness and Accidents

Fatigue Related AccidentsFatigue Related Accidents

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Meter Reading ErrorsMeter Reading Errors

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Fully AlertFully Alert

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Rela

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Biological Rhythms

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15

10

5

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Time of Day & Major Accidents

Bhopal01:00

Chernobyl01:23

Three Mile Island04:00

MidnightNoon Noon

Exxon Valdez Disaster

Cleanup cost: $2 Billion

Exxon Fined: $5 Billion

Environmental damage: ?$

Health Hazards

• Short effects:• sleep disturbance

• Poor concentration • Decrease alertness• Decrease safety

• Prolonged exposure to chemical and biological substances and other hazards

• Long effects:• GI problem• Reproductive effects• Cancer• Exacerbation of

• Sleep disorders • Asthma • Diabetes mellitus • Coronary Artery Disease

GI Dis.• 75% of night

workers vs. 20% of day workers

• Complaints– Loss of appetite– Constipation – Dyspepsia– Heart burn– Abdominal pain– Flatulence

• Many problems may not show up until years later

• Reasons– Poor food quality– More caffeine– More alcohol– More tobacco– Drugs used to

keep awake

Cardiovascular problems

• Increased incidence of ischemic disease

• May be related to:• disturbance of circadian

blood pressure and pulse rate• Substance abuse more likely

in shift workers• Elevated triglyceride levels in

phase advance workers

Hypertension

• Shift workers were found to have approximately 25% greater chance of developing hypertension than non shift workers

Cancer

• At least three nights per month for 15 or more years may increase the risk of Colorectal cancer in women 35%

• Shorter durations also have increased risk• Due to the suppression of melatonin production

with nocturnal light exposure. Melatonin has anti-neoplastic properties

• Breast Cancer , Attributed to inhibition of melatonin production by light exposure during the night

Cognitive Ability

• Recent studies have found deterioration in

cognitive ability in shift workers vs. non shift

workers.

• This increases with duration of exposure

• The effect seems to diminish 4 years after

discontinuation

Medical evaluation:

• History:• CAD• GI dx• Sleep dx• Epilepsy• diabetes • Asthma• Difficulty in night vision

Psychological• Shift workers

demonstrate:• More depression and

despondency• More likely to use

psychotropic drugs or require hospitalization

• Will have magnification of underlying depression or bipolar disorders

• Circadian rhythm disturbance may be a cause for depression

Social Impact

• Increases• Divorce• Family violence• Social Isolation• Sexual dysfunction• May affect women more than men

• Impaired logical reasoning and decision-making

• Impaired vigilance and attention

• Slowed mental operations

• Loss of situational awareness

• Slowed reaction time

• Short cuts

Fatigue Effects on Performance

Major Fatigue Factors

• Time of Day: between midnight and 6 AM

• Cumulative Sleep Debt:

• Acute Sleep Debt:

More than 17 hours since the last sleep period

• Continuous Hours Awake:

Less than eight hours in last 24 hrs.

More than eight hours accumulation.

Shift work type:

1. Fixed pattern • Night • Evening

2. Rotating pattern• Clockwise (morning- evening- night)

• Rapid (less than 4 days)• slow (more than 4 days)

• Counter clockwise (night-evening- morning)

• Rapid • slow

3. Oscillating shift work

4. Split shift work

5. Relief Shift work

Quickly rotating shift system:

• Minimize sleep deprivation (Fischer et al., 1997)

• Minimize circadian rhythm disruption (Knauth 1993, 1995)

• Improve social contacts (Knauth 1993, 1995)

• Improve alertness and well-being (Williamson & Sanderson 1986, Phillips et al., 1991)

Clockwise rotation:• Better tolerated by the

shift workers,Improve production & well-being (Czeisler et al., 1982)

• Improve sleep quality (Folkard 1993)

• Reduce physical, social and psychological problems (Landén 1981)

Shift work Maladaptation

• 15-20% of workers• Signs & symptoms:

• Sleep dis.• Fatigue• Behavioral dis.• GI dis.• Sedative drugs usage

Shift work Maladaptation:

• Age > 50• Morning type• Second job or heavy house work• Long sleep time• Fixed & regular sleep pattern• Hx sleep dis.• Hx GI dis.• Hx cardiovascular dis.• Asthma,DM,Epilepsy

How to keep worker alert?• High illumination level• Breaks• Naps• Occasional stirring music• Stretching or light exercise• Social interaction• Snacks & caffeinated beverages• FDA recommended use Modafinil (Provigil)

for shift work sleep disorder

Suitable Shift systems:

• Daily work: not be more than 8 hr.• Number of night or evening shifts: as small as

possible.• A full day of free time follow every night shift• Contain consecutive work-free days, preferably

including the weekend • Clockwise rotation• Rapid • Shorter shift ( < 8hr) : heavy manual work• Longer shift (12hr) : light job

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