Original article

Scand J Work Environ Health 2011;37(5):411-417    pdf

doi:10.5271/sjweh.3168 | Published online: 28 Apr 2011, Issue date: Sep 2011

The effects of sleep duration on the incidence of cardiovascular events among middle-aged male workers in Japan

by Hamazaki Y, Morikawa Y, Nakamura K, Sakurai M, Miura K, Ishizaki M, Kido T, Naruse Y, Suwazono Y, Nakagawa H

Objectives Although previous epidemiological studies have investigated the relationship between sleep duration and various cardiovascular events, the results have been inconsistent. Accordingly, we conducted a follow-up survey to investigate the relationship between sleep duration and cardiovascular events among male workers, accounting for occupational factors that might confound the true relationship.

Methods A total of 2282 male employees aged 35–54 years based in a factory in Japan were followed for 14 years. The risk of cardiovascular events was compared among 4 groups stratified based on sleep duration at baseline (<6, 6–6.9, 7–7.9, and ≥8 hours). Cardiovascular events included stroke, coronary events and sudden cardiac death. The hazard ratios for events were calculated using a Cox proportional hazards model, with the 7–7.9-hour group serving as a reference. The model was adjusted for potential confounders including traditional cardiovascular risk factors and working characteristics.

Results During 14 years of follow-up, 64 cardiovascular events were recorded including 30 strokes, 27 coronary events and 7 sudden cardiac deaths. After adjustment for possible confounders, the hazard ratios for cardiovascular and coronary events in the <6-hour group were 3.49 [95% confidence interval (95% CI) 1.30–9.40] and 4.95 (95% CI 1.31–18.73), respectively. There was no significant increment in the risk of stroke for any sleep duration groups.

Conclusion Short sleep duration (<6 hours) was a significant risk factor for coronary events in a Japanese male working population.