Working more than 55 hours is linked to a huge increased risk of stroke and also coronary heart disease, according to a study published in The Lancet.
The study—the largest in its field—found a 33% greater risk of stroke and a 13% increased risk of developing CHD. It involved more than 600,000 people and compared people who worked long hours, opposed to a standard 35-40 hour week.
Researchers from the University College London conducted a systematic review and meta-analysis of 25 studies—published and unpublished—of 603,838 people from Europe, the US and Australia, examining the effects of longer working hours on cardiovascular disease.
Participants were followed for an average of 8.5 years up August 20 last year. The results took into account other risk factors, such as age, sex and socioeconomic status.
Additionally, analysis of data from 17 studies of more than 520,000 people who were followed for an average of 7.2 years, found a 1.3 times higher risk of stroke in people working 55 hours or more a week, compared with those who worked standard hours.
The connection remained, even after taking into account health behaviours such as smoking, alcohol consumption, and physical activity, and standard cardiovascular risk factors including high blood pressure and high cholesterol.
The researchers found that the longer people worked there was an incremental risk of stroke. For example, compared with people who worked standard hours, those working between 41 and 48 hours had a 10% higher risk of stroke, and those who worked 49 to 54 hours had a 27% increased risk of stroke.
According to one of the researchers, Mika Kivimäki, a Professor of Epidemiology, pooling all available studies on this topic allowed them to investigate the association between working hours and cardiovascular disease risk with greater precision than has previously been possible.
“Health professionals should be aware that working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease,” says Prof Kivimäki.
Commenting on the results, Dr Urban Janlert from Umeå University in Sweden, said long working hours are not a “negligible” occurrence.
Among OECD countries, Turkey has the highest proportion of people working more than 50 hours a week, while the Netherlands had the lowest.
“For all OECD countries, a mean of 12% of employed men and 5% of employed women work more than 50 hours per week,” says Dr Janlert.
“Although some countries have legislation for working hours, the EU Working Time Directive, which 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.”
The researchers conclude that the causal mechanisms of these relationships need to be better understood, that high risk behaviours, such as lack of exercise, high alcohol consumption, stress, may well increase the risk of stroke.