People who work long hours have a much higher risk of stroke and a slightly greater risk of coronary heart disease than those working a standard week, a major new study suggests.
The research, published in the Lancet, is the largest ever of its kind and involved more than 600,000 people.
It found that those who work 55 hours or more per week have a one-third greater risk of stroke compared with those who work a standard week.
Data from 25 studies involving 603,838 men and women from Europe, the US, and Australia, who were followed for an average of 8.5 years, also found a 13 per cent increase in the risk of coronary heart disease for those who worked similar patterns.
This was defined as a new diagnosis, hospitalisation, or death in people working 55 hours or more per week, compared with those putting in a regular 35- to 40-hour week, even after taking into account risk factors including age, sex, and socioeconomic status.
Professor of epidemiology at University College London (UCL) Mika Kivimäki and colleagues carried out the meta-analysis and systematic review of published studies and unpublished individual data examining the effects of longer working hours on cardiovascular disease up to August 20th, 2014.
Data analysis
Analysis of data from 17 studies involving 528,908 men and women, who were followed for an average of 7.2 years, found a 1.3 times higher risk of stroke in those working 55 hours or more a week compared with those working standard hours.
The researchers found this association remained even after taking into account health behaviours such as smoking, alcohol consumption, physical activity, and standard cardiovascular risk factors including high blood pressure and high cholesterol.
Compared with people who worked standard hours, those working between 41 and 48 hours had a 10 per cent higher risk of stroke, and those working between 49 to 54 hours had a 27 per cent increased risk of stroke.
“Although the causal mechanisms of these relationships need to be better understood, the authors suggest that increasing health-risk behaviours, such as physical inactivity and high alcohol consumption, as well as repetitive triggering of the stress response, might increase the risk of stroke,” the researchers said.
Prof Kivimäki said the pooling of all available studies on the topic allowed the team to investigate the association between working hours and cardiovascular disease risk with greater precision than had 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,” he said.
‘Not negligible’
Dr Urban Janlert from Umeå University in Sweden said long working hours were "not a negligible occurrence".
"Among member countries of the Organisation for Economic Cooperation 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 (2003/88/EC) 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.”