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SLEEP AND HEALTH
ers that the age-standardized prevalence was 5.6% at 15 years of shift work experience
compared with 3.5% for no exposure. Nagaya et al. (2002) found that
markers of insulin resistance were more frequent in shift workers above the age
of 50 than in day workers. Other indicators, such as body mass index, glucose
levels and so forth, give a rather inconclusive impression as indicated in a review
by Boggild and Knutsson (1999).
Another contributing factor to gastrointestinal diseases might be the association
between shift work and smoking. A number of studies have reported that smoking
is more common among shift workers (Angersbach et al., 1980; Knutsson,
Åkerstedt and Jonsson, 1988). Studies concerned with alcohol consumption comparing
day workers and shift workers have produced conflicting results (Smith,
Colligan and Tasto, 1982; Knutsson, 1989a; Romon, Nuttens and Fievet, 1992),
probably due to local cultural habits. One study, which used g-glutamyltransferase
as a marker of alcohol intake, did not indicate that the shift workers had
a higher intake of alcohol than the day workers (Knutsson, 1989a).
Sickness absence is often used as a measure of occupational health risks.
However, sickness leave is influenced by many irrelevant factors and cannot be
considered as a reliable measure of true morbidity. Studies on sickness absence in
day and shift workers have revealed conflicting results and there is no evidence
that shift workers have more sickness absence than day workers (for review, see
Harrington, 1978).
2.3.4.3 Conclusion
Shift work or similar arrangements of work hours clearly affects sleep and alertness
and there is a moderate risk of cardiovascular and gastrointestinal disease. Other
diseases such as cancer or diabetes may be related to shift work but the evidence is
as yet rather weak.
The present review suggests that the risk of disturbed sleep increases with age but
there also seems to be a recent stress-related increase in sleep disturbance in young
adults. The long-term health consequences are not yet understood.
The relation between gender and disturbed sleep is confusing. Females, as a rule,
complain more of sleep problems, but do not exhibit any objective indications of
more disturbed sleep, at least not among otherwise healthy women. With increasing
age the sleep of males deteriorates whereas that of women is relatively well
upheld. Pregnancy, however, is a period of increased risk of disturbed sleep, whereas
the menstrual cycle and menopause show less evidence of sleep disturbance.
Clearly there is a great need for longitudinal research on gender and sleep and, in
particular, on the possible health consequences connected with pregnancy.
Stress due to work or family seems to be one of the major causes of disturbed sleep.
The link to the risk of insomnia is well-established, but reduced sleep in itself seems
to yield the same physiological changes as stress. This suggests that several of the
major civilization diseases in Europe and the United States (diabetes, cardiovascular
diseases and burnout) could be mediated via disturbed sleep. This link clearly
warrants longitudinal studies with interventions.
Shift workers constitute a group that suffers from disturbed sleep for most of their
occupational life. The reason is the interference of work hours with the normal timing
of sleep. This leads to an increased risk of accidents, directly due to excessive
sleepiness, but also to cardiovascular and gastrointestinal diseases, although it is
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