Seasonal variations in hospital admissions for affective disorders by gender and ethnicity.

Hospital admission statistics for depression and mania have shown significant seasonal patterns. The present investigation was conducted to establish the pervasiveness of the impact of seasons on mood disorder presentation at Birmingham (52 degrees North) by gender and ethnicity. Non-mood disorder admissions were examined as a control to determine the specificity of any seasonal variation to affective illness. Case notes for 992 admissions, during January-December 1995 inclusive, to an inpatient unit were reviewed retrospectively. Admission data were broken down by gender and into three ethnic groups: Asian, white and black. Seasonality in admissions for depression, bipolar disorder and non-mood disorders was tested by gender and ethnicity. Admission frequencies for depression showed significant seasonal pattern, with the incidence of depression being highest in winter. Total admissions, bipolar and non-mood disorders did not show any significant seasonal variability. A gender effect was evident on seasonality of admissions for affective illness, with significant winter peak for depression and summer peak for bipolar disorder in women only. The Asian group was the only ethnic group that showed significant seasonal variation in depression, with a greater number of depressive episodes in winter. Environmental variables were related significantly to the incidence of mood disorders. Specific seasonal effect for affective illness was evidenced by the non-existence of seasonality in other psychiatric disorders. The reverse seasonal pattern for depression and mania suggests a maladaptive response of vulnerable individuals to specific functions of seasons.