title: Association between vitamin D and depressive symptoms varies by season: Results from the German Health Interview and Examination Survey for Adults (DEGS1).
abstract: Findings from epidemiological studies regarding seasonal variations in the association between vitamin D status and depression are inconsistent.
  
  
  
  Cross-sectional analysis of data from 6331 participants aged 18-79 years in the nationwide representative German Health Interview and Examination Survey for Adults 2008-2011 (DEGS1). Associations between 25-hydroxy-vitamin-D (25(OH)D) serum levels in quartiles and current depressive symptoms as measured by the Patient Health Questionnaire depression module (PHQ-9) and defined as severity of depressive symptoms (PHQ-9 score, range 0-27 points) and elevated depressive symptoms (PHQ-9 score ≥10 points) were analysed using multivariable linear and logistic regression adjusted for sociodemographic, biological and lifestyle factors. Analyses were stratified by summertime (May to October) and wintertime (November to April) because of evidence for interaction with season (p≤0.01).
  
  
  
  In crude analyses, vitamin D status was inversely associated with both depression outcomes in summertime but not in wintertime. After adjustment for potential confounders, a significant association with severity of depressive symptoms remained in summer, with 0.73 point lower PHQ-9 scores in the highest versus lowest quartile. The association between 25(OH)D quartiles and elevated depressive symptoms in summertime was less strong and no longer significant in fully adjusted models.
  
  
  
  Participants with severe depression may be underrepresented in DEGS1. Residual confounding cannot be excluded.
  
  
  
  25(OH)D serum levels were inversely associated with current depressive symptoms in summer but not in wintertime. The fact that the association is stronger in summertime suggests that vitamin D deficiency may be a consequence rather than a cause of depression.
authors.affiliation: Robert Koch Institute, Department of Epidemiology and Health Monitoring, General-Pape-Str. 62-66, D-12101 Berlin, Germany. Electronic address: RabenbergM@rki.de.
authors.forename: Martina
authors.initials: M
authors.lastname: Rabenberg
authors.affiliation: Robert Koch Institute, Department of Epidemiology and Health Monitoring, General-Pape-Str. 62-66, D-12101 Berlin, Germany.
authors.forename: Cordula
authors.initials: C
authors.lastname: Harisch
authors.affiliation: Berlin School of Public Health, Charité-Universitätsmedizin Berlin, Seestr. 73, D-13347, Berlin, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Rieckmann
authors.affiliation: Robert Koch Institute, Department of Epidemiology and Health Monitoring, General-Pape-Str. 62-66, D-12101 Berlin, Germany; Faculty of Life Sciences and Medicine, King's College London, Guy's Hospital, St Thomas Street, SE1 9RT London, United Kingdom.
authors.forename: Amanda K
authors.initials: AK
authors.lastname: Buttery
authors.affiliation: Robert Koch Institute, Department of Epidemiology and Health Monitoring, General-Pape-Str. 62-66, D-12101 Berlin, Germany.
authors.forename: Gert B M
authors.initials: GB
authors.lastname: Mensink
authors.affiliation: Robert Koch Institute, Department of Epidemiology and Health Monitoring, General-Pape-Str. 62-66, D-12101 Berlin, Germany.
authors.forename: Markus A
authors.initials: MA
authors.lastname: Busch
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D003863:Depression / Q000097:blood* / Q000175:diagnosis; D003865:Major Depressive Disorder / Q000097:blood; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood*; D055815:Young Adult
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D