Seasonal variation in suicides and in admissions to hospital for mania and depression

Background: The influence of seasons on mood disorders is controversial. Objective: To examine monthly variations in admissions for mania and depressions including variations with sex and age and correlations with frequencies of suicides. Methods: All admissions for mania or depression (N=4341) in a population of 1,800,000 with 35,285 admissions in the years 1992–1996 were analysed. All 14,503 suicides in Norway the years 1969–1996 were also analysed. Results: Admissions for depression had a significant monthly variation for women (χ2=29.78, df=11, P<0.005) with the highest peak in November and for men (χ2=19.69, df=11, P<0.05) with the highest peak in April. Among women increasing age correlated negatively with the range of monthly observed/expected ratios (rs=−0.943, N=6, P<0.01) and with a of maximal monthly observed/expected ratio (rs=−0.943, N=6, P<0.01). Among men suicides correlated with admissions for depression (r=0.647, N=12, P<0.05) and mania (r=0.678, N=12, P<0.05). Limitations: The time of admission to hospital are not identical to onset of affective episode. The study was done retrospectively. No sociocultural or physical environmental data were investigated. Conclusion: A hypothesis of an influence of seasons on mood disorders is supported. Younger women seem to be especially vulnerable.