The impact of a delayed sleep-wake schedule on depression is greater in women--A web-based cross-sectional study in Japanese young adults.

Sleep-related problems, such as symptoms of insomnia, daytime sleepiness, shorter sleep duration, or a delayed sleep-wake schedule, are known to be risk factors for depression. In general, depression is more prevalent in women than in men, but sleep-related problems do not necessarily show similar gender predominance. Hence, it can be speculated that the impact of sleep-related problems on the development process of depression differs between genders; however, so far, few studies have focused on this issue. The aim of this study was to clarify gender differences in the rates of depression of people with the above sleep-related problems, and to examine gender differences in factors associated with depression in Japanese young adults. A web-based questionnaire survey comprising assessments of demographic variables, sleep-related variables (bed time, wake time, sleep onset latency, frequency of difficulty in initiating sleep and that in maintaining sleep, i.e. symptom components of insomnia, and daytime sleepiness), and the 12-item version of the Center for Epidemiologic Studies Depression Scale was administered to 2502 participants (males:females = 1144:1358, age range = 19-25 years). Female predominance in the rate of depression was observed only in subjects with a delayed sleep-wake schedule (χ(2)(1) = 15.44, p < 0.001). In men, daytime sleepiness and difficulty in initiating sleep were significantly associated with depression (odds ratio [OR] = 2.39, 95% confidence interval [CI] = [1.69, 3.39], p < 0.001; OR = 3.50, 95% CI = [2.29, 5.35], p < 0.001, respectively), whereas in women, significant associations were found between depression and a delayed sleep-wake schedule (OR = 1.75, 95% CI = [1.28, 2.39], p < 0.001), daytime sleepiness (OR = 2.13, 95% CI = [1.60, 2.85], p < 0.001), and difficulty in initiating sleep (OR = 4.37, 95% CI = [3.17, 6.03], p < 0.001). These results indicate that in younger generations, the impact of a delayed sleep-wake schedule on the development of depression is greater in women; specifically, women are vulnerable to depression when they have an eveningness-type lifestyle, which is possibly attributable to the female-specific intrinsic earlier and shorter circadian rhythm. These results suggest the necessity of gender-based approaches to treating sleep-related problems for alleviating or preventing depressive symptoms in young adults.