Seasonality, social zeitgebers and mood variability in entrainment of mood: Implications for seasonal affective disorder

Background: Seasonal variations in mood (seasonality) appear to be entrained to light, a physical zeitgeber. We hypothesised that people high in seasonality may be responsive to a range of zeitgebers, because of greater mood variability. We investigated whether the moods of people high in seasonality were more strongly entrained to the calendar week, a social zeitgeber, and whether any such effect was dependent on variability of mood. Methods: 53 participants (14 male, 39 female; overall mean age=30) completed a daily mood report, over 56 consecutive days. Participants also completed the Seasonality Score Index (SSI) of the Seasonal Pattern Assessment Questionnaire. Each participant’s time series of daily mood was analysed by spectral analysis to quantify the strength of their weekly mood cycle. Results: Participants with high SSI scores (≥11) had significantly stronger weekly mood cycles than those with low SSI scores (