LONDON, Aug. 20 (UPI) -- Working 55 or more hours per week can increase the risk for having a stroke by a third, as well as increase risk for developing heart disease, regardless of other factors in life, researchers found in a large review of studies.
The risk for stroke was found to increase with the number of hours beyond 40 a person worked each week. Increased risk for stroke, as well as heart disease, remained even when researchers considered standard risk factors such as age, health status and health-realted behaviors.
"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," said Mika Kivimäki, a professor at University College London, in a press release. "Health professionals should be aware that working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease."
The researchers analyzed data for 603,838 men and women collected during 25 studies in Australia, Europe and the United States who were followed for an average of 8 1/2 years. None of the participants had coronary heart disease at the start of the studies. Risk for a new diagnosis, hospitalization or death connected to heart disease was found to be 13 percent higher among people who worked 55 hours per week or more when compared to those who worked 35 to 40 hours per week.
Data from 17 studies that involved 528,908 people who were followed for an average of just over 7 years, had a 33 percent higher chance of having a stroke if they worked more than 55 hours per week. In the case of having a stroke, the number of hours people worked was related to risk factor -- working between 41 and 48 hours increased risk by 10 percent, and working 49 to 54 hours increased the risk by 27 percent, researchers reported.
In the case of both heart disease and stroke, the increased risks remained, even when age, sex and economic status, as well as smoking, alcohol consumption, physical activity and blood pressure were considered.
The study is published in The Lancet.