People who work long hours have an increased risk of developing an irregular heart rhythm, according to a major study involving UK researchers.
Compared to people who had a normal working week of 35-40 hours, those who worked 55 hours or more were around 40% more likely to develop atrial fibrillation during the following decade.
“These findings show that long working hours are associated with an increased risk of atrial fibrillation”
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.
The findings, published in the European Heart Journal, were based on nearly 85,500 men and women from the UK, Denmark, Sweden and Finland, none of whom had atrial fibrillation at the start.
Researchers assessed working hours between 1991 and 2004, classified as less than 35 a week, 35-40 – standard working hours – 41 to 48, 49 to 54, and 55 hours or more a week.
During the 10-year follow-up, there were 1,061 new cases of atrial fibrillation, said the researchers from the Individual-Participant-Data Meta-analysis in Working Populations (IPD-Work) Consortium.
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 1,000, the researchers concluded.
“The suggestion that longer working hours may be a cause of atrial fibrillation is very interesting”
Lead study author Professor Mika Kivimaki, from University College London, said: “These findings show that long working hours are associated with an increased risk of atrial fibrillation, the most common cardiac arrhythmia.
“This could be one of the mechanisms that explain the previously observed increased risk of stroke among those working long hours,” he said. “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.
“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 Professor Kivimaki.
Nine out of 10 of the atrial fibrillation cases occurred in people free of pre-existing or concurrent cardiovascular disease, suggesting the increased risk was likely to reflect the effect of long working hours rather than the effect of any pre-existing or concurrent cardiovascular disease, he said.
Professor Kivimaki highlighted that a 40% increased extra risk was an “important hazard” for people who already have a high overall risk of cardiovascular disease due to other risk factors.
However, he noted that for a healthy, young person, the absolute increased risk of atrial fibrillation associated with long working hours was small.
Working long hours ‘increases risk of atrial fibrillation’
Professor Kivimaki added: “The great strength of our study was its size, with nearly 85,000 participants, which makes it large by the standard of any study in this field.”
In an accompanying editorial in the same journal, academics from the Netherlands warned that job type and shifts patterns, which could potentially affect the findings, were not explored in the new research.
Also commenting on the findings, Professor Sir Nilesh Samani, medical director at the British Heart Foundation, highlighted that many patients developed atrial fibrillation without an obvious cause.
“The suggestion that longer working hours may be a cause of atrial fibrillation is very interesting,” he said.
“Significantly, this study clearly shows that the link between atrial fibrillation and long working hours has nothing to do with the other, already known, risk factors for the condition,” he added.
However, he also noted that the observational nature of the research meant the findings could not confirm for definite the cause of this relationship.