Shift work raises the chances of having a heart attack, a major review of working pattern health effects has shown.
Working unsocial hours was found to increase the chances of a heart attack by more than a fifth, with the risk of a stroke rising by 5%.
Shift patterns, especially night shifts, have long been linked to high blood pressure, high cholesterol levels and diabetes.
But experts have disagreed about their association with heart and artery disease.
The new research, the largest analysis of shift work and heart risk to date, pulled together evidence from 34 studies involving more than two million people.
Coronary events — including heart attacks and angina — and strokes were more common among shift workers.
The chances of “any coronary event” were increased by 24%, and of heart attacks by 23%, while stroke risk was raised slightly by 5%. Despite the relatively small effect, the impact on a large population could be significant.
In Canada, where some of the researchers were based, 7% of heart attacks were linked to shift work.