By Angela Gonzalez
People working 55 hours or more a week had an approximately 40% higher risk of atrial fibrillation compared with people working 35 to 40 hours a week, a large multi-cohort, 10-year study has found.
Nine out of ten incident atrial fibrillation cases occurred among those free of pre-existing or concurrent cardiovascular disease, suggesting that “observed excess risk of atrial fibrillation is likely to reflect a direct link of long working hours to atrial fibrillation rather than an indirect link via cardiovascular disease,” reported first author Mika Kivimaki (University College London, London, UK and University of Helsinki, Helsinki, Finland) and others in the European Heart Journal.
Other studies have suggested that long working hours are associated with increased risk of stroke; however, “little is known about the role of long working hours as a potential risk factor of atrial fibrillation,” the authors argue. Therefore, they set out to investigate, in a prospective multi-cohort study from the Individual-Participant-Data Meta-analysis in Working Populations (IPD-Work) Consortium, 85,494 men (n=29,579) and women (n=55,915) (mean age 43.4 years) with no recorded history of atrial fibrillation who were based in the UK, Denmark, Sweden and Finland.
The participants were followed-up for 10 years and working hours were assessed at study baseline from 1991‒2004. After follow-up, the researchers identified 1,061 new cases of atrial fibrillation using data on electrocardiograms, hospital records, drug reimbursement registers and death certificates. The 10-year cumulative incidence was 12.4 per 1,000 individuals.
The authors reported that in 71.4% of cases, atrial fibrillation was diagnosed before the age of 65. Of the incident atrial fibrillation cases, 86.7% had no cardiovascular disease during the study period and only 10.2% had pre-existent cardiovascular disease when atrial fibrillation was first recorded.
After adjusting for age, sex and socioeconomic status, participants who worked long hours had a 1.4-fold increased risk of atrial fibrillation compared with those working standard hours. “Long working hours were associated with a slightly poorer lifestyle profile at baseline characterised by a higher prevalence of obesity, leisure-time physical inactivity, smoking and risky alcohol use,” write Kivimaki et al. However, after additional adjustment for lifestyle factors, the authors found a marginal association between long vs. standard working hours and incident atrial fibrillation (1.41, 95% CI 1.10-1.80, p=0.0059, I2=0%, p=0.62).
After adjustment for pre-existing coronary heart disease at the time of atrial fibrillation diagnosis, the association between long working hours and atrial fibrillation remained (1.41, 95% CI 1.12-1.78, p=0.0039) and after excluding participants with cardiovascular disease at baseline (n=549, hazard ratio 1.14, 95% CI 1.11‒1.79, p=0.0054) or cardiovascular disease at baseline or follow-up (n=2006, hazard ratio=1.36, 95% CI=1.05‒1.76, p=0.0180).
There was not difference in the association between long working hours and atrial fibrillation between men and women, participants younger than 50 and those 50 years or older at baseline or by socioeconomic group.
Kivimaki et al note that the mechanisms underlying the association between long working hours and atrial fibrillation are not known. Nonetheless, they comment that there has been a suggestion of a link between extensive overtime working and autonomic nervous system abnormalities, which is a risk factor for atrial fibrillation. “As such, stress-related mechanisms that may trigger arrhythmia, such as autonomic dysfunction, might be a more promising focus for future studies on long working hours and atrial fibrillation than mediation via classic cardiovascular disease risk factors,” the researchers write and emphasise that further research is needed to determine mechanisms underlying the link between long working hours and atrial fibrillation. Generalisability of these findings to other countries remains to be confirmed.
Regarding the implications of these findings in public health, Kivimaki told Cardiac Rhythm News: “We do not know whether the risk of atrial fibrillation would decrease by reducing working hours. For this reason, the only advice I can give to those working long hours is to adopt a heart healthy lifestyle: getting enough sleep, engaging in daily physical activity, eating (and drinking) healthily, maintaining a healthy weight, avoiding smoking, reducing high blood pressure and controlling cholesterol and glucose levels. This will reduce the overall risk of atrial fibrillation.”
The researchers are currently examining the effects of stress in people with pre-existing cardiovascular disease.
The IPD-Work Consortium was supported by NordForsk, a Nordic Research Programme on Health and Welfare, the EU New OSH ERA research programme, the Finnish Work Environment Fund, Finland, the Swedish Research Council for Working Life and Social Research, Sweden, Danish National Research Centre for Working Environment, Demark, and the UK Medical Research Council.