title: Autoimmune diseases and severe infections as risk factors for mood disorders: a nationwide study.
abstract: OBJECTIVE
  Mood disorders frequently co-occur with medical diseases that involve inflammatory pathophysiologic mechanisms. Immune responses can affect the brain and might increase the risk of mood disorders, but longitudinal studies of comorbidity are lacking.
  
  
  OBJECTIVE
  To estimate the effect of autoimmune diseases and infections on the risk of developing mood disorders.
  
  
  METHODS
  Nationwide, population-based, prospective cohort study with 78 million person-years of follow-up. Data were analyzed with survival analysis techniques and adjusted for calendar year, age, and sex.
  
  
  METHODS
  Individual data drawn from Danish longitudinal registers.
  
  
  METHODS
  A total of 3.56 million people born between 1945 and 1996 were followed up from January 1, 1977, through December 31, 2010, with 91, 637 people having hospital contacts for mood disorders.
  
  
  METHODS
  The risk of a first lifetime diagnosis of mood disorder assigned by a psychiatrist in a hospital, outpatient clinic, or emergency department setting. Incidence rate ratios (IRRs) and accompanying 95% CIs are used as measures of relative risk.
  
  
  RESULTS
  A prior hospital contact because of autoimmune disease increased the risk of a subsequent mood disorder diagnosis by 45% (IRR, 1.45; 95% CI, 1.39-1.52). Any history of hospitalization for infection increased the risk of later mood disorders by 62% (IRR, 1.62; 95% CI, 1.60-1.64). The 2 risk factors interacted in synergy and increased the risk of subsequent mood disorders even further (IRR, 2.35; 95% CI, 2.25-2.46). The number of infections and autoimmune diseases increased the risk of mood disorders in a dose-response relationship. Approximately one-third (32%) of the participants diagnosed as having a mood disorder had a previous hospital contact because of an infection, whereas 5% had a previous hospital contact because of an autoimmune disease.
  
  
  CONCLUSIONS
  Autoimmune diseases and infections are risk factors for subsequent mood disorder diagnosis. These associations seem compatible with an immunologic hypothesis for the development of mood disorders in subgroups of patients.
authors.affiliation: National Centre for Register-Based Research, Aarhus University, Aarhus, Denmark. benros@ncrr.dk
authors.forename: Michael E
authors.initials: ME
authors.lastname: Benros
authors.forename: Berit L
authors.initials: BL
authors.lastname: Waltoft
authors.forename: Merete
authors.initials: M
authors.lastname: Nordentoft
authors.forename: Søren D
authors.initials: SD
authors.lastname: Ostergaard
authors.forename: William W
authors.initials: WW
authors.lastname: Eaton
authors.forename: Jesper
authors.initials: J
authors.lastname: Krogh
authors.forename: Preben B
authors.initials: PB
authors.lastname: Mortensen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001327:Autoimmune Diseases / Q000150:complications / Q000453:epidemiology*; D015897:Comorbidity; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D007239:Infections / Q000150:complications / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D019964:Mood Disorders / Q000453:epidemiology* / Q000209:etiology; D011446:Prospective Studies; D012042:Registries; D012307:Risk Factors; D012720:Severity of Illness Index; D055815:Young Adult