First author Manav Vyas, a graduate student, and professor Amit Garg, both of Western University in London, Ontario, and colleagues analyzed the results of 34 studies involving more than 2 million people to investigate the association between shift work and major vascular events.
Shift work was defined as evening shifts, irregular or unspecified shifts, mixed schedules, night shifts and rotating shifts. The control groups were non-shift, day, workers or the general population.
Among the 2,011,935 people in the studies, 17,359 had some kind of coronary event -- 6,598 had heart attacks, and 1,854 had ischemic strokes caused by lack of blood to the brain.
The study, published in the British Medical Journal, found shift work was associated with an increased risk of heart attack at 23 percent, coronary events at 24 percent and stroke at 5 percent.
However, night shifts were associated with the steepest increase in risk for coronary events at 41 percent.
In Canada -- where 32.8 percent of workers worked on shifts during 2008 to 2009 -- 7 percent of heart attacks, 7.3 percent of coronary events and 1.6 percent of ischemic strokes could be attributed to shift work.