The biological effects
of shift work
Shift Work
Overview of key effects
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:
night, morning & afternoon
Shift Work & risk of Coronary Heart
Disease in Women
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
Night-shift work is linked with an increased
risk of breast cancer
ALSO
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
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
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
•
•
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
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