Objective: Depression due to long work hours and sleep deprivation is a major occupational health concern. The extent to which work hours and sleep are associated with depression was investigated in employees of small- and medium-scale businesses in the Japanese city of Yashio, Saitama, and in the Ohta ward of Tokyo, a suburb of Tokyo, controlling for various potential confounders.

Method: In this cross-sectional study, a total of 2,643 full-time employees (1,928 men and 715 women), aged 18-79 years (mean = 45 years), in 296 small- and medium-scale businesses were surveyed from August 2002 to December 2002 using a self-administered questionnaire evaluating work hours, sleep status, and covariates including sociodemographic and socioeconomic factors, health behaviors, biological factors, medication usage, and occupational factors. Depression was assessed using the Center for Epidemiologic Studies Depression Scale. Prevalence of depression by work hours, sleep status, and covariates was analyzed by χ² test. Risk of depression by work hours, sleep status, and both combined was estimated by multivariate logistic regression analysis.

Results: Participants working > 10 hours per day, sleeping < 6 hours per day, and reporting insufficient sleep were, respectively, 37%, 43%, and 97% more likely to be depressed than those working 6 to 8 hours per day, sleeping 6 to < 8 hours per day, and reporting sufficient sleep (P < .05). Participants working > 10 hours per day or > 8 to 10 hours per day with < 6 hours per day of sleep showed a 41%-169% higher prevalence of depression versus those working 6 to 8 hours per day with 6+ hours per day of sleep (P < .05). Participants reporting insufficient sleep in 3 work-hour categories (6 to 8, > 8 to 10, and > 10 hours per day) showed a 62%-179% increase in the prevalence of depression versus those working 6 to 8 hours per day and reporting sufficient sleep (P < .05). No significant effects on depression were found for subjects in any work-hour category with 6+ hours of sleep or with subjective sufficient sleep.

Conclusions: Depression associated with long work hours is primarily a result of sleep deprivation. Greater attention should be paid to management of sleep deprivation to prevent workplace depression.