You might want to consider telling the boss “no” every now and then.  A study published in The Lancet published today suggests those who work more than 55 hours a week have between a 1-3 times higher risk of stroke than those who more a more typical work week, regardless of gender, and a weaker association between working longer hours and risk for heart attack.

The study is a meta-analysis, which uses statistical methods for looking for data correlations across different cohort studies (a cohort study attempts to identify risk prospectively by measuring patients over longer periods of time).  In this case, the authors analyzed data from 25 studies from 24 different  in Europe, Australia, and the US.  The combined population across all the studies was over 600,000 men and women who had no evidence of coronary heart disease in advance of the various study designs.

The authors attempted to control for confounding factors such as smoking, drinking alcohol, weight problems, exercise, and underlying cholesterol, blood pressure issues, or diabetes.  One of the methods for controlling for these factors was to eliminate disease events which occurred early in the observation periods (within a few years of the original cohort designs).

Of the 603, 838 people free from heart disease at baseline in the study group, 4768 had an a heart event within a mean follow-up time of 8 and one half years, while of the 528, 908 people free from stroke signs at baseline, 1722 had a stroke event in a mean follow-up time of 7.2 years.  Compared to normal risk, this represents a 13% higher likelihood of getting a heart attack, and a 33% higher risk of getting a stroke.

Lead author for the work was Miki Kivimäki from the Department of Epidemiology and Public Health, University College London.

“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,” Kivimäki said in an accompanying release.