Working 55 hours or more a week can increase the chances of suffering a stroke by a third compared to those working 40 hours or less. 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.
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.”
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.
“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. 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. “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.