London - Working 55 hours or more a week can increase the chances of suffering a stroke by a third compared to the risk for those who work 40 hours or less.
Researchers have also found a significant but smaller increased risk of developing coronary heart disease - 13 percent more likely in people who worked long hours.
An analysis of 17 previously published studies, on nearly 530 000 men and women who were followed for an average period of 7.2 years, found they were 33 percent more likely to suffer a stroke if they worked 55 hours or more.
The link still existed even when individual differences in factors such as smoking, drinking and physical activity were taken into account. Significantly, the longer people worked, the greater the risk they run - with those working between 41 and 48 hours having a 10 percent higher risk of stroke, and those working 49 to 54 hours having a 27 percent increased risk.
The study, published in the journal The Lancet, also looked at data gathered by 25 previous studies involving more than 600 000 men and women in Europe, the US and Australia who were monitored for an average of 8.5 years. It found a 13 percent increased risk of heart disease for workers who put in 55 hours or more each week compared with those who worked the standard 40 hours or less.
“The pooling of all available studies on this topic allowed us to investigate the association between working hours and cardiovascular disease risk with greater precision than has previously been possible,” said Professor Mika Kivimaki of University College London, the lead author of the study.
“Health professionals should be aware that working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease,” he said.
The findings did not vary between men and women, or between geographical regions, and did not depend on the method of diagnosing strokes, which suggests that the findings are “robust”, the researchers said.
Advising on the results' implications, researchers said: “Employees who work long hours have a higher risk of stroke than those working standard hours; the association with coronary heart disease is weaker. These findings suggest that more attention should be paid to the management of vascular risk factors in individuals who work long hours.”
The reasons for the increased risk of stroke or heart disease cannot be explained, but it may be related to the extra stress of long hours, or unhealthy behaviours linked to long hours such as lack of physical activity or high alcohol consumption after work, the researchers suggested.
The Independent