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Long working hours linked to heightened irregular heart rhythm risk

Those working 55+hours/week 40% more likely to develop atrial fibrillation

Caroline White

Friday, 14 July 2017

Long working hours are linked to a heightened risk of developing atrial fibrillation, finds a study* of nearly 85,500 men and women published in the European Heart Journal today.

Compared with people who worked a normal week of between 35-40 hours, those who worked 55 hours or more were around 40% more likely to develop atrial fibrillation over the following decade, the findings show.

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 monitoring period.

Professor Mika Kivimaki, from the Department of Epidemiology at University College London, who led the research, 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. 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.”

The research team, which included contributors from the Individual-Participant-Data Meta-analysis in Working Populations (IPD-Work) Consortium, analysed data from 85,494 men and women from the UK, Denmark, Sweden and Finland.

They assessed the participants’ working hours between 1991 and 2004. Working hours were classified as fewer than 35 hours a week, 35-40 hours, the standard for 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 to begin with.

During the 10-year monitoring period, 1,061 new cases of atrial fibrillation emerged, giving an incidence rate of 12.4 per 1,000 people.

But among the 4,484 people working 55 hours or more, the incidence was 17.6 per 1,000, meaning that their risk of developing the condition was 1.4 times higher, even after accounting for influential factors, such as age, sex, socioeconomic status, obesity, leisure time exercise, smoking and risky drinking.

“Nine out of 10 of the atrial fibrillation cases occurred in people who were free of pre-existing or concurrent cardiovascular disease. 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,” said Professor Kivimaki.

“A 40% 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,” he suggested.

“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 added.

Working hours were only assessed once at the beginning of the study and type of job (for instance, whether it involved working night shifts) wasn’t recorded either.

But Professor Kivimaki said: “In the current absence of trials with atrial fibrillation as the primary outcome in the general population, findings from observational studies such as this are particularly important in offering insights into the lifestyle determinants of this condition.”

In an linked editorial,** Drs Bakhtawar Mahmoodi and Lucas Boersma, of St Antonius Hospital, Nieuwegein, The Netherlands, caution: “Despite the efforts of the authors to thoroughly assess the reported association between long working hours and atrial fibrillation, there are many inherent limitations of the data that preclude definite conclusions on acknowledging long working hours as an independent risk factor for atrial fibrillation.”

* Kivimäki M, Nyberg ST; Batty GD, et al. Long working hours as a risk factor for atrial fibrillation: a multi-cohort study. European Heart Journal, published: 13 July 2017. DOI: 10.1093/eurheartj/ehx324

** Mahmoodi BK; Boersma LV. Do long working hours predispose to atrial fibrillation? European Heart Journal, published: 13 July 2017. DOI: 10.1093/eurheartj/ehx385

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