Over a 6-year period, a Canadian study of 1000 patients younger than 60 years who returned to work after a first myocardial infarction (MI) found that those working 55 hours a week or more had a twofold increased risk for recurrent coronary heart disease (CHD) events (iMI or unstable angina), compared with those working 35 to 40 hours per week, even after adjustment for socio-demographics, lifestyle-related risk factors, clinical risk factors, work environment factors, and personality factors.
"These results showed a linear risk increase after 40 h/week and a stronger effect after the first 4 years of follow-up and when long working hours are combined with job strain," reported Dr Xavier Trudel, of CHU de Québec-Laval University Research Centre in Quebec City, and colleagues.
In their study, they suggested secondary prevention interventions to curb the number of working hours among patients at risk of CHD recurrence: For example, long working hours should be assessed routinely to improve the prognosis of post-MI patients, the team urged.
Writing in an accompanying editorial, Dr Jian Li, of University of California – Los Angeles (UCLA), and Dr Johannes Siegrist, of Heinrich-Heine-University of Düsseldorf, Germany, agreed: A "short standardised assessment of working time and stressful working conditions among economically active cardiac patients would enrich physicians' awareness of patients' needs and inform medical decision making."
"With the transformation of the modern work due to technological advances and economic globalization, an increase in work-load and an extension of irregular, nonstandard forms of employment, including working from home, were reported, aggravating the control and prevention of long working hours," Li and Siegrist wrote.
They urged cardiac rehabilitation programmes to offer "training skills of coping with stressful demands and of strengthening resilience and relaxation" and the involvement of occupational health services in developing return-to-work plans.
Workplaces with returning cardiac disease patients will need to adopt tailored, multi-disciplinary programmes (cognitive behavioural therapy, coaching) to boost job retention and disease management, Li and Siegrist added.
The prospective cohort study included 967 MI survivors under age 60 who were recruited from 30 hospitals across Canada's Quebec province in 1995-1997. Medical records showed that 205 people had a recurrent CHD event over follow-up averaging 5.9 years. Those working the most hours after an MI tended to be men and people in their 40s and 50s.
Job strain, defined as a combination of high psychological demands and low decision latitude at work, was measured using 18 items from the Job Content Questionnaire. Each person's work hours were assessed just once, at about 6 weeks after returning to work. "Some patients could have changed exposure during follow-up, leading to potential nondifferential misclassification and to an underestimation of the true effect," Trudel's group acknowledged.
The observational study was also subject to potential unmeasured confounding, the researchers noted. Moreover, women (for whom previous research has linked work stress to heart risk) accounted for only about one in 10 participants, limiting the generalisability of the study's results.
"In conclusion, the study by Trudel et al provides a new piece of research evidence that work-related factors play an important role in CHD prognosis," Li and Siegrist wrote. "Occupational health services are urgently needed to be incorporated into cardiac rehabilitation programs and secondary prevention of CHD."
Long Working Hours and Risk of Recurrent Coronary Events
Xavier Trudel, Chantal Brisson, Denis Talbot, Mahée Gilbert-Ouimet, Alain Milot
Published in the Journal of the American College of Cardiology in April 2021
Evidence from prospective studies has suggested that long working hours are associated with incident coronary heart disease (CHD) events. However, no previous study has examined whether long working hours are associated with an increased risk of recurrent CHD events among patients returning to work after a first myocardial infarction (MI).
The purpose of this study was to examine the effect of long working hours on the risk of recurrent CHD events.
This is a prospective cohort study of 967 men and women age 35 to 59 years who returned to work after a first MI. Patients were recruited from 30 hospitals across the province of Quebec, Canada. The mean follow-up duration was 5.9 years. Long working hours were assessed on average 6 weeks after their return to work. Incident CHD events (fatal or nonfatal MI and unstable angina) occurring during follow-up were determined using patients’ medical files. Hazard ratios were estimated using Cox proportional hazard regression models. Splines and fractional polynomial regressions were used for flexible exposure and time modeling.
Recurrent CHD events occurred among 205 patients. Participants working long hours (≥55 h/week) had a higher risk of recurrent CHD events after controlling for sociodemographics, lifestyle-related risk factors, clinical risk factors, work environment factors, and personality factors (hazard ratio vs. 35 to 40 h/week: 1.67; 95% confidence interval: 1.10 to 2.53). These results showed a linear risk increase after 40 h/week and a stronger effect after the first 4 years of follow-up and when long working hours are combined with job strain.
Among patients returning to work after a first MI, longer working hours per week is associated with an increased risk of recurrent CHD events. Secondary prevention interventions aiming to reduce the number of working hours among these patients may lower the risk of CHD recurrence.
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