People who work long hours may have an increased risk of developing irregular heart rhythm, scientists have warned.
A study shows that compared to people who worked a normal week of between 35-40 hours, those who worked 55 hours or more were about 40 per cent more likely to develop atrial fibrillation during the following 10 years.
For every 1,000 people in the study, an extra 5.2 cases of atrial fibrillation occurred among those working long hours during the 10 year follow-up.
"These findings show that long working hours are associated with an increased risk of atrial fibrillation, the most common cardiac arrhythmia," said Professor Mika Kivimaki, from the University College London (UK), who led the research.
"This could be one of the mechanisms that explain the previously observed increased risk of stroke among those working long hours," said Kivimaki.
"Atrial fibrillation is known to contribute to the development of stroke, but also other adverse health outcomes, such as heart failure and stroke-related dementia," said Kivimaki.
Researchers analysed data from 85,494 men and women from the UK, 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 atrial fibrillation at the start of the studies.
During the ten-year follow-up period, there were 1,061 new cases of atrial fibrillation.
This gave an incidence rate of 12.4 per 1,000 people in the study, but among the 4,484 people working 55 hours or more, the incidence was 17.6 per 1000.
"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," said Kivimaki.
"Nine out of ten of the atrial fibrillation cases occurred in people who were free of pre-existing or concurrent cardiovascular disease," he said.
This suggests the increased risk is likely to reflect the effect of long working hours rather than the effect of any pre-existing or concurrent cardiovascular disease, but further research is needed to understand the mechanisms involved.
"A 40 per cent increased extra risk is an important hazard for people who already have a high overall risk of cardiovascular disease due to other risk factors such as older age, male sex, diabetes, high blood pressure, high cholesterol, overweight, smoking and physical inactivity, or living with an established cardiovascular disease," said Kivimaki.
"For a healthy, young person, with few if any of these risk factors, the absolute increased risk of atrial fibrillation associated with long working hours is small," he said.
Lead photograph: Dadang Tri/Reuters. Used for representational purposes only.