Impact of frequency of nightmares comorbid with insomnia on depression in Japanese rural community residents: A cross-sectional study

Nightmares were likely to occur in participants with insomnia than in those who did not have insomnia. Both nightmares and insomnia were associated with aggravation of depression. Participants with both nightmares and insomnia had a higher comorbid rate of depression. Insomnia and nightmares independently impacted aggravation of depression. Objective: Nightmares and insomnia are known to be associated with the development and aggravation of depression. Our community-based study was conducted to clarify the relation between the impacts of nightmares and insomnia on depression. Methods: A cross-sectional questionnaire-based survey was administered to residents of a rural community in Japan. In all, 2822 participants responded to questions assessing personal characteristics, the Pittsburgh Sleep Quality Index (PSQI) for assessing insomnia, and a 12-item version of the Center for Epidemiological Studies Depression scale (CES-D) for evaluating depression. Nightmare frequency was assessed using an item for nightmares on the PSQI. Results: Nightmares more frequently occurred in participants with insomnia than those without (P<01). Multiple regression analysis revealed that the scores of both nightmares and insomnia were significantly associated with the increase in depression score (nightmares (β=0.09, P<01); insomnia (β=0.39, P<01)). Participants with coexisting nightmares and insomnia showed higher depression scores than participants with insomnia alone or those with nightmares who did not have insomnia (P<01). Conclusions: Insomnia and nightmares independently and additively impact the aggravation of depression.