Working late at the office on a regular basis can increase the risk of having a stroke or heart disease, a study has found.
Scientists found that working 55 hours or more a week can increase the chances of suffering a stroke by a third compared to the risk for people who work the regular 40 hours or less.
The researchers also found a significant but smaller increased risk of developing coronary heart disease, which was 13 per cent more likely in people who worked long hours compared to the normal working week.
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 per cent more likely to suffer a stroke if they worked 55 hours or more compared with people who worked 40 hours or less per week.
The link still existed even when individual differences in factors such as smoking, drinking and physical activity were taken into account. Importantly, the longer people worked each week, the greater the risk they run, with those working between 41 and 48 hours having a 10 higher risk of stroke and those working 49 to 54 hours having a 27 per cent 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 per cent 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 together suggest that the findings are “robust”, the researchers said.
Writing on the implications of the results, the researchers concluded: “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, the researchers suggested.
Whatever the reasons, the findings are the strongest indication that there is a causal link between long working hours and strokes, said Urban Janlert of Umea University in Sweden, in a comment article published in The Lancet.
“Long working hours are not a negligible occurrence. Among member countries of the Organisation for Economic Co-operation and Development (OECD), Turkey has the highest proportion of individuals working more than 50 hours per week (43 per cent), and the Netherlands the lowest (less than 1 per cent). For all OECD countries, a mean of 12 per cent of employed men and 5 per cent of employed women work more than 50 hours per week,” Dr Janlert said.
“Although some countries have legislation for working hours - for example, the EU Working Time Directive gives people the right to limit their average working time to 48 hours per week - it is not always implemented. Therefore, that the length of a working day is an important determinant mainly for stroke, but perhaps also for coronary heart disease, is an important finding,” he said.
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