Employees who work 55 or more hours per week are 33% more at risk of having a stroke than those who complete a “standard” 35 to 40-hour week, UK researchers have found.
A study, published in The Lancet, found the link remained even after taking into account health and lifestyle factors such as smoking, alcohol consumption, blood pressure and cholesterol levels.
It also found the longer people worked, the higher their chances of a stroke.
“Working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease”
Compared with people who worked standard hours, those working 41 to 48 hours had a 10% higher risk of stroke, and those working 49 to 54 hours had a 27% increased risk.
Researchers at University College London found the association after analysing existing data from 17 studies involving around 530,000 men and women.
They also analysed data from 25 studies of more than 600,000 men and women and found working 55 or more hours per week also increased the risk of coronary heart disease – by 13% – compared with people who worked a “standard” week.
This was true even after taking into account risk factors including age, sex, and socioeconomic status, said the researchers.
They noted that previous studies had found the risk of coronary heart disease was raised in employees working long hours by about 40%, but said several limitations in these studies could have biased the estimates.
Few studies had previously examined long working hours as a risk factor for stroke, they added, although stress and extensive sitting – both of which are associated with long working – could increase its risk.
“If long working hours present a danger to health, it should be possible to change them”
Study author Professor Mika Kivimaki said: “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.
“Health professionals should be aware that working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease.”
Commenting on the findings, Dr Urban Janlert from Sweden’s Umea University said: “Working conditions are important determinants of people’s health. Some of these conditions might be difficult to change because of the nature of the work, but the length of a working day is a human decision.
“Essentially, if long working hours present a danger to health, it should be possible to change them, which is not always the case with other work environmental factors,” he said.
He noted that among countries in the Organisation for Economic Cooperation and Development – which includes the UK, US, France and Germany – an average of 12% of employed men and 5% of employed women work more than 50 hours per week.
“Although some countries have legislation for working hours – such as the EU Working Time Directive that gives people the right to limit their average working time to 48 hours per week – it is not always implemented,” he added.