Stroke Risk with Long Work Hours

A recent study may have given new meaning to the phrase “working yourself into an early grave.” The systematic review and meta-analysis included data from over 600,000 people, and suggested that long work hours can increase the risk of stroke by 33%. The risk of coronary heart disease (CHD) was also increased, but to a lesser extent than stroke.

Studies have suggested that long work hours could contribute to the development of cardiovascular disease, but most of the evidence comes from studies about CHD. Though both stress and sitting for long hours can increase the risk for stroke, not many studies have looked at long work hours and the risk for stroke. Other issues associated with long work hours, such as heavy drinking, may also increase the risk for stroke.

“Sudden death from overwork is often caused by stroke and is believed to result from a repetitive triggering of the stress response,” wrote first author Mika Kivimäki of University College in London, UK and colleagues with the Individual-Participant-Data Meta-analysis in Working Populations (IPD-Work) Consortium.

In the study, researchers conducted a search for prospective cohort studies published in English in PubMed and Embase from inception until August 20, 2014. They also did manual reviews of reference lists in selected publications, and did a citation search in Web of Science. Researchers addressed the possibility of publication bias by including unpublished data from 20 cohort studies housed in open access archives and from the IPD-Work Consortium.

The analysis included 25 studies from Europe, the USA, Israel, and Australia. The meta-analysis of CHD included 603,838 people, and the meta-analysis of stroke included 528,908 people. Standard work hours were considered 35-40 hours/week, while long work hours were considered ≥55 hours/week. Additional analyses were adjusted for age, sex, socioeconomic status, reverse causation (the possibility that employees with underlying CVD reduced their work hours in the period before a CV event), and different research methods for identifying stroke.

Results showed:

• Long work hours were linked to:

♦ 33% increased risk of stroke (relative risk [RR] 1.33, 95% CI 1.11-1.61, p=0.002)

♦ 13% increased risk of CHD (RR 1.13, 1.02-1.26, p=0.02)

• After adjustment, the link between long work hours and increased risk for stroke remained (range of RR estimates 1.30-1.42).

• A dose-response relationship between long work hours and increased risk for stroke (p_trend <0.0001):

♦ 41-48 hours: 10% increased stroke risk (RR 1.10, 0.94-1.28, p=0.24)

♦ 49-54 hours: 27% increased stroke risk (RR 1.27, 1.03-1.56, p=0.03)

♦ ≥55 hours: 33% increased stroke risk (RR 1.33, 1.11-1.61, p=0.002)

“[O]ur meta-analysis shows that employees who work long hours have a higher risk of stroke than those working standard hours. However, the evidence for coronary heart disease is less persuasive,” the authors concluded. “Our findings suggest that more attention should be paid to the management of vascular risk factors in individuals who work long hours.”

Take Home Points

• Working ≥55 per week may increase the risk of stroke by 33%.
• Working ≥55 per week may increase the risk of CHD by 13%.
• Vascular risk factors in employees who work long hours should receive greater attention.

Reference: Kivimäki M, et al. Long working hours and risk of coronary heart disease and stroke: a systematic review and meta-analysis of published and unpublished data for 603 838 individuals. Lancet. 2015 Aug 19.