Longer work week linked to increase in stroke risk

by Bruce Sylvester: Persons who work over 55 hours  per week have a 33% increased risk of stroke and a 13% increased risk of developing coronary heart disease compared with persons who work 35-40 hours per week, researchers reported on August 19, 2015 in The Lancet.

“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,” said investigator Mika Kivimäki, Professor of Epidemiology at University College London, UK.

Kivimäki, and his colleagues conducted a  systematic review of relevant studies, pooling and analyzing the data on the effects of longer working hours on cardiovascular disease, and up to August 20, 2014.

Analysis of 25 studies enrolling 603,838 men and women who had been followed for an average of 8.5 years, found a 13% increased risk of incident coronary heart disease (a new diagnosis, hospitalization, or death) in subjects working 55 hours or more per week compared with those working 35 to 40 hour week, even after adjustments for age, sex, and socioeconomic status.

Analysis of data from 17 studies enrolling 528,908 men and women followed for an average of 7.2 years, found a 1.3 times higher risk of stroke in individuals working 55 hours or more a week compared with those working 35-40 hours. This association held after the researchers adjusted for smoking, alcohol consumption, physical activity, high blood pressure and high cholesterol.

Notably, the longer the hours they worked, the higher their chances of a stroke. Compared with subjects working 35-40 hours, those working between 41 and 48 hours had a 10% higher risk of stroke, and those working 49 to 54 hours had a 27% increased risk of stroke.

In a linked Comment, Dr Urban Janlert from Umeå University in Sweden said, “Long working hours are 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 h per week (43%), and the Netherlands the lowest (<1%). For all OECD countries, a mean of 12% of employed men and 5% of employed women work more than 50 h per week. Although some countries have legislation for working hours–eg, the EU Working Time Directive (2003/88/EC) gives people the right to limit their average working time to 48 h 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.”