People who work long hours have an increased risk of developing atrial fibrillation (AFib), according to a study published July 13 in the European Heart Journal.

Mika Kivimaki, MD, et al., analyzed data from 85,494 men and women from the U.K., Denmark, Sweden and Finland who took part in one of eight studies in these countries. They assessed the participants’ working hours when they joined the studies between 1991 and 2004. Working hours were classified as less than 35 hours a week, 35–40 hours, which was considered as the standard working hours of full–time workers, 41 to 48 hours, 49 to 54 hours, and 55 hours or more a week. None of the participants had AFib at the start of the studies.

The results of the study showed that, compared with people who worked a normal week of 35–40 hours, those who worked 55 hours or more were approximately 40 percent more likely to develop AFib during the following 10 years. For every 1,000 people in the study, an extra 5.2 cases of AFib occurred among those working long hours during the 10–year follow–up.

According to Kivimaki, “those who worked long hours had a 1.4 times higher risk of developing atrial fibrillation, even after we had adjusted for factors that could affect the risk, such as age, sex, socioeconomic status, obesity, leisure time physical activity, smoking and risky alcohol use.”