Eveningness and seasonality are associated with the bipolar disorder vulnerability trait

Trait theories of vulnerability to bipolar disorder (BD) are increasingly common in the literature, yet poorly understood. The aim of the current study was to complement existing knowledge of trait theories by investigating two biological rhythm features often associated with BD – eveningness and seasonality – in a sample assessed as vulnerable to the disorder. Two hundred and thirteen participants completed an online survey consisting of the General Behavior Inventory, Seasonal Pattern Assessment Questionnaire, and Morningness-Eveningness Questionnaire. Hierarchical regressions controlling for sex and age showed that greater levels of seasonality and a tendency towards an eveningness chronotype were weak, but significant predictors of the BD vulnerability trait. When the traits of vulnerability to depression and mania were investigated separately, seasonality and eveningness were significant predictors of the former, but only seasonality was a significant predictor of the latter. The Autumn/Winter pattern of seasonality was a weak predictor of trait vulnerability to mania but not depression. The current findings advance understanding of the BD vulnerability trait, and may have consequences for the behavioural management of those who are considered to be ‘at risk’ of the disorder.