Seasonal changes in clinical status in bipolar disorder: a prospective study in 1000 STEP-BD patients

Objective: To investigate seasonal and regional effects on bipolar I and II patients. Method: The Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD) patients were prospectively examined for monthly change in prevalence rates of depressed and recovered clinical status over the year. General Estimating Equation modeling was used to assess the effect of season on prevalence rates. Additionally, patients were stratified by bipolar subtype and by region. Results: A significantly higher prevalence rate of depression is observed in the northern sites, a significant prevalence by month effect is found only in the bipolar II patients. Conclusion: The prevalence of depression is greater in patients from the northern vs. southern STEP-BD sites. Seasonal peak prevalence rates of depression differ by region. Bipolar II patients were more ill year-round and demonstrated greater monthly fluctuation in prevalence rates of being ill than did bipolar I patients. We conclude that seasonal effects upon bipolar patients vary by region and bipolar subtype.