Seasonal variation of manic and depressive symptoms in bipolar disorder

Analyses of seasonal variation of manic and depressive symptoms in bipolar disorder in retrospective studies examining admission data have yielded conflicting results. We examined seasonal variation of mood symptoms in a prospective cohort with long-term follow-up: the Collaborative Depression Study (CDS).

The CDS included participants from five academic centers with a prospective diagnosis of bipolar I or II disorder. The sample was limited to those who were followed for at least 10 years of annual or semi-annual assessments. Time series analyses and autoregressive integrated moving average (ARIMA) models were used to assess seasonal patterns of manic and depressive symptoms.

A total of 314 individuals were analyzed (bipolar I disorder, n = 202; bipolar II disorder, n = 112), with both disorders exhibiting the lowest frequency of depressive symptoms in summer and the highest around the winter solstice, though the winter peak in symptoms was statistically significant only with bipolar I disorder. Variation of manic symptoms was more pronounced in bipolar II disorder, with a significant peak in hypomanic symptomatology in the months surrounding the fall equinox.

Significant seasonal variation exists in bipolar disorder, with manic/hypomanic symptoms peaking around the fall equinox and depressive symptoms peaking in the months surrounding the winter solstice in bipolar I disorder.