Evening preference is related to the incidence of depressive states independent of sleep-wake conditions

Although evening preference has recently been identified as a risk factor for depression, it has not been substantiated whether evening preference is a direct risk factor for depressive states, or if it is associated secondarily through other factors, such as delayed sleep timing and shortened sleep duration. The objective of this study is to investigate associations in Japanese adult subjects between evening preference and incidence of depressive states, adjusting for various sleep parameters related to depressive states. The Morningness-Eveningness Questionnaire (MEQ), the Pittsburgh Sleep Quality Index (PSQI), and the Center for Epidemiologic Studies Depression Scale (CES-D) were administered to 1170 individuals (493 males/677 females; mean and range 38.5 and 20-59 yrs) to assess their diurnal preferences, sleeping states, and presence of depression symptoms. Subjects were classified into five chronotypes based on MEQ scores. Evening preference was associated with delayed sleep timing, shortened sleep duration, deteriorated subjective sleep quality, and worsened daytime sleepiness. Logistic regression analysis demonstrated that the extreme evening type (odds ratio OR]?=?1.926, p?=?.018) was associated with increased incidence of depressive states and that the extreme morning type (OR?=?0.342, p?=?.038) was associated with the decreased incidence of depressive states, independent of sleep parameters, such as nocturnal awakening (OR?=?1.844, p?