The findings of a large study in the Journal of Affective Disorders demonstrated a seasonal pattern for manic, depressive, and mixed episodes in women with bipolar disorder.
National register data were provided by Statistics Austria for all hospitalizations because of bipolar disorder from 2001 to 2014. Patients labeled with diagnostic codes indicating remission, bipolar disorder unspecified, or “other” bipolar disorder were excluded, as were patients who had been hospitalized for >1 year.
A total of 60,607 admissions were grouped into manic (39.6%), depressive (34.4%), and mixed (30.5) episodes. Patients were on average age 47.56 years at the time of admission.
For manic episodes, admissions for men peaked in June, and for women admissions peaked in September. Admissions for depressive episodes peaked in November for women, with no apparent pattern for men. Men also did not exhibit a seasonal pattern for mixed episodes, whereas women were admitted most frequently in June.
Thus, for men, the only significant seasonal association was manic episode admissions during the summer. Significant seasonal patterns were detected for women regardless of the type of episode, with summer-autumn manic episodes, winter depressive episodes, and summer mixed episodes.
Although women with bipolar disorder appeared to be more susceptible to the season, the distinction was not statistically significant across sex. Across age groups, younger women (15 to <35 years) experienced more seasonal inpatient admissions.
As the study examined inpatient admissions, the findings might be limited to a severely ill population. Additionally, the study was conducted in Austria, and seasonal pattern might be affected by location and regional climate.
Fellinger M, Waldhoer T, König D, et al. Seasonality in bipolar disorder: Effect of sex and age [published online September 20, 2018]. J Affect Disord. doi:10.1016/j.jad.2018.09.073