title: Seasonal variation in bipolar disorder.
abstract: BACKGROUND
  In patients with bipolar disorder, admissions for manic and depressive episodes frequently display a seasonal pattern. We examined this variation and compared the patterns with the seasonal admission rates for schizophrenia.
  
  
  METHODS
  Patients with bipolar disorder or schizophrenia were identified from the Finnish Hospital Discharge Register of in-patient admissions to all psychiatric hospitals during the years 1969-91. They were included in the analysis if the first admission had occurred before 30 years of age. A total of 295 bipolar patients were found, and a sample of 295 schizophrenic patients was randomly selected for comparison.
  
  
  RESULTS
  There was no seasonal variation among all hospital admissions for bipolar disorder or schizophrenia. However, the first admission for a depressive compared with a manic episode of bipolar disorder occurred significantly more often in the autumn (33% v. 21% respectively). The peak difference occurred during the week after the autumnal equinox in September.
  
  
  CONCLUSIONS
  Our findings suggest that there is no seasonal variation in bipolar disorder, although in some patients the clinical course might be influenced by the autumn, as far as the likelihood of a first admission for depression is concerned.
authors.affiliation: Department of Mental Health, National Public Health Institute, Helsinki, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Partonen
authors.forename: J
authors.initials: J
authors.lastname: Lönnqvist
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000175:diagnosis / Q000453:epidemiology* / Q000523:psychology; D003430:Cross-Sectional Studies; D003866:Depressive Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000523:psychology; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D010343:Patient Admission / Q000706:statistics & numerical data; D012559:Schizophrenia / Q000175:diagnosis / Q000453:epidemiology; D012565:Schizophrenic Psychology; D012621:Seasons