Working Hours and Risk of Acute Myocardial Infarction and Stroke Among Middle-Aged Japanese Men - The Japan Public Health Center-Based Prospective Study Cohort II.

Background: Evidence from prospective cohort studies regarding the relationship between working hours and risk of cardiovascular disease is limited.

Methods and results: The Japan Public Health Center-Based Prospective Study Cohort II involved 15,277 men aged 40-59 years at the baseline survey in 1993. Respondents were followed up until 2012. During the median 20 years of follow up (257,229 person-years), we observed 212 cases of acute myocardial infarction and 745 stroke events. Cox proportional hazards models adjusted for sociodemographic factors, cardiovascular risk factors, and occupation showed that multivariable-adjusted hazard ratios (HRs) associated with overtime work of ≥11h/day were: 1.63 (95% confidence interval [CI] 1.01-2.63) for acute myocardial infarction and 0.83 (95% CI 0.60-1.13) for total stroke, as compared with the reference group (working 7 to <9 h/day). In the multivariable model, increased risk of acute myocardial infarction associated with overtime work of ≥11 h/day was more evident among salaried employees (HR 2.11, 95% CI 1.03-4.35) and men aged 50-59 years (HR 2.60, 95% CI 1.42-4.77).

Conclusions: Among middle-aged Japanese men, working overtime is associated with a higher risk of acute myocardial infarction.