Shift Work is bad for health – British Medical Journal

Objective To synthesise the association of shift work with major
vascular events as reported in the literature.

Data sources Systematic searches of major bibliographic databases,
contact with experts in the field, and review of reference lists of
primary articles, review papers, and guidelines.

Study selection Observational studies that reported risk ratios for
vascular morbidity, vascular mortality, or all cause mortality in
relation to shift work were included; control groups could be
non-shift (“day”) workers or the general population.

Data extraction Study quality was assessed with the Downs and Black
scale for observational studies. The three primary outcomes were
myocardial infarction, ischaemic stroke, and any coronary event.
Heterogeneity was measured with the I2 statistic and computed random
effects models.

Results 34 studies in 2 011 935 people were identified. Shift work was
associated with myocardial infarction (risk ratio 1.23, 95% confidence
interval 1.15 to 1.31; I2=0) and ischaemic stroke (1.05, 1.01 to 1.09;
I2=0). Coronary events were also increased (risk ratio 1.24, 1.10 to
1.39), albeit with significant heterogeneity across studies (I2=85%).
Pooled risk ratios were significant for both unadjusted analyses and
analyses adjusted for risk factors. All shift work schedules with the
exception of evening shifts were associated with a statistically
higher risk of coronary events. Shift work was not associated with
increased rates of mortality (whether vascular cause specific or
overall). Presence or absence of adjustment for smoking and
socioeconomic status was not a source of heterogeneity in the primary
studies. 6598 myocardial infarctions, 17 359 coronary events, and 1854
ischaemic strokes occurred. On the basis of the Canadian prevalence of
shift work of 32.8%, the population attributable risks related to
shift work were 7.0% for myocardial infarction, 7.3% for all coronary
events, and 1.6% for ischaemic stroke.

Conclusions Shift work is associated with vascular events, which may
have implications for public policy and occupational medicine.