The biological effects
of shift work
Shift Work
Overview of key effects
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Shift work causes many healthrelated effects
Disruption of circadian rhythms
affects physiological function
Shift work = health problems: poorer
health habits increase vulnerability
to illness
Biggest effect: Sleep disruption
Three principal shifts:
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night, morning & afternoon
Shift Work & risk of Coronary Heart
Disease in Women
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The study - Kawachi et al. 1988
 79 109 women
 42 to 67 years - free of diagnosed CHD
and stroke
 rotating night shifts - at least three
nights p/m in addition to day and
evening shifts
6 or more years of shift work may increase
the risk of CHD in women
De-synchronisation
of circadian rhythms
Fast rotating shift
work changes
secretary patterns
of melatonin,
prolactin, cortisol
and testosterone
(Touitou et al, 1989)
Shift work affects
patterns of sleep
and wakefulness
• Disrupts circadian rhythms &
mechanism of sleep
• The most troublesome symptoms
are:
• difficulty getting to sleep,
• shortened sleep
• drowsiness during working hours
• No clear indication that long-term
shift work causes chronic sleep
problems (Åkerstedt, 2003)
Risk of cancer in female Nurses
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Night-shift work is linked with an increased
risk of breast cancer
ALSO
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Exposure to light at night suppresses the
production of melatonin, a hormone that
inhibits intestinal cancers
Night shift at least 3 nights p/m for 15yrs or
more may increase the risk of colorectal
cancer (Schernhammer et al. 1988)
Shift work:
Impact on metabolic syndrome
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Increased risk of cardiovascular
disease
Obesity and high triglycerides
levels in men & women
Obesity more prevalent
among women in all
groups, but only in
two out of four age
groups in men
(Karlsson et al. 2003)
Other health disorders
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Peptic ulcers
Coronary heart disease
Compromised pregnancy
outcome (Knutsson, 2001)
Influence of night shift work on
psychological state
• Night shift - associated with psychological complaints
• Study: 18 healthy nurses (age 29; +/-2 yrs)
• Rapid shift rotation system (day work, 8:15-17:15;
evening work, 16:00-22:00; night work, 21:30-8:30)
• Assess psychologic states using a validated
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questionnaire.
High scores for confusion, depression, anger-hostility,
fatigue and tension-anxiety
Lowest scores for energy after a night shift
Does shift work lead to
poorer health habits?
• Sent out questionnaire - 2299 respondents
– Selected 506 who has always done shift work
– 183 workers who had never done shift work
• Shift workers smoke more & tend to be more
overweight than day workers (KivimÄki et al.,
2001)
The effects of short-term night-shift working
• Short period (5 days) of night-shift
• Ten nurses (8 female, 2 male; age 28.1 +/- 1.7
• Finding:
– pituitary-adrenal responses to CRH are
markedly disrupted
– mimic abnormalities seen in patients with
chronic fatigue syndrome