Association between eveningness and depressive symptoms in daytime workers: A cross-sectional analysis of the Aichi Workers' Cohort Study.

Objectives: Eveningness (evening preference in chronotype) has been reported to be associated with a number of psychiatric problems. We examined a cross-sectional association between eveningness and depressive symptoms in daytime workers.

Methods: The subjects were 4410 civil servants (71.7% male, aged 18-69 years [mean, 43.5 years]) with no history of depressive disorder who did not perform shift work, and for whom there were no missing data. The association between eveningness, determined using the reduced Morningness-Eveningness Questionnaire, and depressive symptoms, determined using the shorter form of the Central Epidemiological Studies Depression scale, was assessed with logistic regression analysis adjusted for potential confounding factors (gender, income, living alone, breakfast intake, coffee consumption, drinking habits, exercise, smoking, working hours, sleep duration, and difficulty falling asleep).

Results: Of the subjects, 529 (12.0%) had eveningness, and 1408 (31.9%) reported depressive symptoms. Depressive symptoms were reported more frequently by those with eveningness than by those with other chronotypes (57.3% vs 28.5%). The association between eveningness and depression (gender- and age-adjusted odds ratio, 3.27; 95% confidence interval, 2.71-3.95) was significant after adjustment for the other confounding factors (odds ratio, 2.40; 95% confidence interval, 1.96-2.95).

Conclusions: Our results suggest that eveningness is associated with depressive symptoms among day workers and that this association is independent of potential confounding factors. Further longitudinal studies are needed to examine the causal relationship.