Abstract
INTRODUCTION: Bipolar disorder is a disorder characterized by cyclic changes in mood, yet limited research has explored longitudinal patterns of seasonality on mood symptoms in this population. This study aimed to examine longitudinal mood symptoms in individuals with bipolar type I and II, and healthy controls to determine if seasonal patterns were present and to validate the Global Seasonality Score as a measure of seasonality. METHODS: Participants from the Prechter Longitudinal Study of Bipolar Disorder were included. Seasonal variations in mood were determined from the Patient Health Questionnaire, Altman Self-Rating Mania scale, and the Seasonal Pattern Assessment Questionnaire. Mixed effects models were utilized to examine the effects of season and diagnostic group on patterns of mood over time. RESULTS: All groups exhibited significant seasonal effects on mood symptoms, with evidence of decreased depressive symptoms and increased mania symptoms in longer daylight months. The Global Seasonality Score showed significant differences between diagnostic groups, with bipolar I and II groups demonstrating higher seasonality than healthy controls. High seasonality was associated with greater variance in mood symptoms. CONCLUSION: The present study found evidence of seasonal patterns in mood symptoms in individuals with bipolar type I and II. These results highlight the need for consideration of seasonality in assessment and treatment in bipolar disorder and suggest that interventions such as light therapy during seasons of heightened risk could be beneficial. The validation of the Global Seasonality Score as a reliable measure further underscores the benefit of utilizing self-report measures to identify periods of vulnerability.