Seasonality and circadian phase delay: Prospective evidence that winter lowering of mood is associated with a shift towards Eveningness

Abstract

Background: Lewy's phase shift hypothesis (PSH) of seasonal affective disorder (SAD) asserts that winter depression is caused by an abnormal delay of circadian phase in winter. The aim of this study was to further investigate the PSH by testing the novel hypothesis that winter pattern seasonality of mood in the general population is associated with a phase delay of circadian rhythms in winter. Methods: Using a random community sample of 244 adults in Melbourne, seasonality of mood was measured prospectively as the within-subject difference between self-reports of behavioural engagement in summer and winter across 3 years. The Horne-Ostberg Morningness-Eveningness questionnaire (MEQ) was used..