SHIFT work may be toxic for more than just one's social life, as the world's biggest study of its health effects has found employees rostered to work outside the traditional business hours of nine to five are nearly 25 per cent more likely to have a stroke or heart attack.
Most of the danger came from heart attacks, which were found to be 23 per cent more common among shift workers, while the risk of stroke caused by a blood vessel blockage increased by 5 per cent compared with non-shift workers.
Although there have previously been suggestions of such risks, the study -- published yesterday in the British Medical Journal -- makes the evidence for the link far stronger by basing its results on an analysis of findings from 34 previous trials that included more than two million people.
The Canadian and Scandinavian authors said all shift work schedules with the exception of evenings were "associated with a statistically higher risk of coronary events", while night shifts were linked to the highest risk, increasing the chance of a heart attack or stroke by 41 per cent.
However, the extra heart attacks and strokes were mostly not lethal, as mortality rates were little different between shift workers and the rest of the population.
The authors, from Canada's Western University in Ontario, the Norwegian University of Science and Technology in Trondheim, and Karolinska Institute in Stockholm, said the study's design could not prove shift work caused the higher risk, but some of the 34 studies had found an increased risk in shift work even after taking account of the fact that shift workers were more likely to have unhealthy habits. "Unhealthy behaviour alone thus cannot fully account for the association between shift work and cardiovascular events," they wrote.
"The increased risk of vascular disease apparent in shift workers, regardless of its explanation, suggests that people who do shift work should be vigilant about risk factor modification."
Robert Grenfell, clinical issues director for the National Heart Foundation, said the study's huge sample meant the association between shift work and heart attacks had been established, and was probably caused by sleep deprivation, reduced opportunities for exercise and taking "the easy option" with food, which he said was "usually the unhealthy one".
"For workers, we know you are probably chasing sleep more than anything else," Dr Grenfell said.
"But you need to look after yourself by making sure you get enough physical activity and get a good diet."