title: Seasonality and bipolar disorder: a systematic review, from admission rates to seasonality of symptoms.
abstract: BACKGROUND
  Bipolar disorder (BD) is a severe mental disorder affecting 1-4% of the population worldwide. It is characterized by periods of (hypo)manic and depressive episodes. Seasonal patterns (SP) may be observed in admission rates, mood relapses and symptom fluctuations.
  
  
  METHODS
  We conducted a systematic review of seasonality in BD, classifying studies based on seasonal admission rates to seasonality of symptoms assessments.
  
  
  RESULTS
  Fifty-one papers were identified of which 32 addressed hospitalization rates by season, 6 addressed categorical diagnoses, and 13 explored symptom dimensions. Seasonal peaks for different BD mood episodes are observed worldwide and widely replicated. Manic episodes peak during spring/summer and, to a lesser extent, in autumn, depressive episodes peak in early winter and, to a lesser extent, summer, and mixed episodes peak in early spring or mid/late summer. There was a high frequency of SP for manic episodes (15%) and depressive episodes (25%), the latter being associated with a more complex clinical profile (BD II subtype, comorbid eating disorders, more relapses and rapid cycling). Finally, there was evidence for greater seasonal fluctuations in mood and behavior in individuals with BD than in those with unipolar depression or 'healthy' controls.
  
  
  CONCLUSIONS
  Sample size, gender distribution, methodological quality and sophistication of the analytical approaches employed varied considerably.
  
  
  CONCLUSIONS
  There is evidence of seasonality in BD, with emerging evidence that climatic conditions may trigger BD symptoms or episodes. A better understanding of the underlying mechanisms would facilitate the development of personalized chronobiological therapeutic and preventive strategies.
authors: Inserm, U1144, Paris F-75006, France; AP-HP, GH Saint-Louis - Lariboisière - Fernand Widal, Pôle Neurosciences, 75475 Paris Cedex 10, France; Université Paris Descartes, UMR-S 1144, Paris, F-75006, France; Université Paris Diderot, UMR-S 1144, Paris, F-75013, France; Fondation FondaMental, Créteil, 94000, France. Electronic address: pierre.a.geoffroy@gmail.com.
authors: Pierre Alexis
authors: PA
authors: Geoffroy
authors: Inserm, U1144, Paris F-75006, France; AP-HP, GH Saint-Louis - Lariboisière - Fernand Widal, Pôle Neurosciences, 75475 Paris Cedex 10, France; Université Paris Descartes, UMR-S 1144, Paris, F-75006, France; Université Paris Diderot, UMR-S 1144, Paris, F-75013, France; Fondation FondaMental, Créteil, 94000, France.
authors: Frank
authors: F
authors: Bellivier
authors: Academic Psychiatry, Institute of Neuroscience, Newcastle University, UK; Centre for Affective Disorders, Institute of Psychiatry, London, UK.
authors: Jan
authors: J
authors: Scott
authors: Fondation FondaMental, Créteil, 94000, France; AP-HP, Hôpital H. Mondor - A. Chenevier, Pôle de Psychiatrie, Créteil, 94000, France; Inserm, U955, Psychiatrie génétique, Créteil, 94000, France.
authors: Bruno
authors: B
authors: Etain
mesh_terms: D000339:Affect; D001714:Bipolar Disorder / Q000175:diagnosis / Q000523:psychology*; D003865:Major Depressive Disorder / Q000523:psychology; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D010343:Patient Admission / Q000706:statistics & numerical data*; D012008:Recurrence; D012621:Seasons
keywords: Bipolar disorders; Circadian rhythms; Depression; Mania; Season; Suicide