A large study has found that people who work 55 hours or more per week have a 33% greater risk of stroke and a 13% greater risk of coronary heart disease than those who work 35 to 40 hours per week. The study is a meta-analysis of data from studies done in Europe, the United States, and Australia.
This analysis includes data on more than 600,000 individuals and is the largest study of the relationship between working hours and cardiovascular health. But the analysis shows a correlation, not whether there is a cause-and-effect relationship between long work hours and the risk of stroke.
Researchers led by Mika Kivimaki of University College London combined the results of multiple studies and tried to account for factors that might skew the results, such as cholesterol levels, high blood pressure, smoking, and physical activity. They also collected information from public databases and received additional data from the authors of previous work.
Seventeen of the studies included nearly 530,000 men and women who were tracked on average 7.2 years. More than 1,700 nonfatal and deadly strokes occurred in this patient population. After controlling for other factors, the researchers found a one-third greater risk of stroke among those workers who reported working 55 or more hours weekly, compared with those who reported working the more-standard 35 to 40 hours.
Kivimaki and his colleagues also found the risk of stroke increased with longer work hours.
The analysis of coronary heart disease in workers included data from 25 studies that involved more than 603,000 people. Some of these studies were evaluated in both the coronary heart disease and in the stroke analysis. After an average of 8.5 years, more than 4,700 received diagnoses of heart disease as a cause of death or hospitalization, or a 13% increase in those who worked long hours over those who did not.
Although the association between stroke and long work hours is strong, it is still not possible to determine if long hours are entirely to blame for the increased risk. Many studies only asked participants once how many hours they worked per week. In addition, it was not determined whether participants felt a lot of stress on their jobs.