Shift work linked to coronary risks

SHIFT WORK may be linked to an increased risk of having a heart attack or stroke, research published this morning suggests.

A large meta-analysis of previously published studies, comprising data on more than two million people, found shift work was associated with a 23 per cent increased risk of heart attack but just a 5 per cent increased chance of having a stroke.

Prof David Hackam and colleagues from the Stroke Prevention and Atherosclerosis Research Centre at the University of Western Ontario in London, Ontario, Canada, say their work is the largest analysis of shift work and vascular risk to date and has implications for public policy and occupational medicine.

Shift work has long been known to disrupt the body clock – or circadian rhythm – and is associated with an increased risk of high blood pressure, high cholesterol and diabetes, but its association with vascular disease has been controversial. Previous studies have shown that even a single overnight shift can increase a person’s blood pressure and impair the normal variability of their heart rate. However, flexible work patterns are a necessary part of a diverse industrial economy.

Recent research has also found an association between shift work and cancer – it found an increased risk of breast cancer among female military employees working night shifts.

For the study published today, shift work was defined as evening shifts, irregular or unspecified shifts, mixed schedules, night shifts and rotating shifts. Employees working from 9am until 5pm were used as controls. Differences in the quality and design of individual studies were taken into account to minimise bias.

The results, published by the British Medical Journal, show night shifts were associated with the steepest increase in risk for coronary events. But the authors acknowledge the absolute increased risk is small.