title: Nine-year risk of depression diagnosis increases with increasing self-reported concussions in retired professional football players.
abstract: BACKGROUND
  Concussions may accelerate the progression to long-term mental health outcomes such as depression in athletes.
  
  
  OBJECTIVE
  To prospectively determine the effects of recurrent concussions on the clinical diagnosis of depression in a group of retired football players.
  
  
  METHODS
  Cohort study; Level of evidence, 2.
  
  
  METHODS
  Members of the National Football League Retired Players Association responded to a baseline General Health Survey (GHS) in 2001. They also completed a follow-up survey in 2010. Both surveys asked about demographic information, number of concussions sustained during their professional football career, physical/mental health, and prevalence of diagnosed medical conditions. A physical component summary (Short Form 36 Measurement Model for Functional Assessment of Health and Well-Being [SF-36 PCS]) was calculated from responses for physical health. The main exposure, the history of concussions during the professional playing career (self-report recalled in 2010), was stratified into 5 categories: 0 (referent), 1 to 2, 3 to 4, 5 to 9, and 10+ concussions. The main outcome was a clinical diagnosis of depression between the baseline and follow-up GHS. Classic tabular methods computed crude risk ratios. Binomial regression with a Poisson residual and robust variance estimation to stabilize the fitting algorithm estimated adjusted risk ratios. χ(2) analyses identified associations and trends between concussion history and the 9-year risk of a depression diagnosis.
  
  
  RESULTS
  Of the 1044 respondents with complete data from the baseline and follow-up GHS, 106 (10.2%) reported being clinically diagnosed as depressed between the baseline and follow-up GHS. Approximately 65% of all respondents self-reported sustaining at least 1 concussion during their professional careers. The 9-year risk of a depression diagnosis increased with an increasing number of self-reported concussions, ranging from 3.0% in the "no concussions" group to 26.8% in the "10+" group (linear trend: P < .001). A strong dose-response relationship was observed even after controlling for confounders (years retired from professional football and 2001 SF-36 PCS). Retired athletes with a depression diagnosis also had a lower SF-36 PCS before diagnosis. The association between concussions and depression was independent of the relationship between decreased physical health and depression.
  
  
  CONCLUSIONS
  Professional football players self-reporting concussions are at greater risk for having depressive episodes later in life compared with those retired players self-reporting no concussions.
authors.affiliation: University of North Carolina at Chapel Hill, CB #8700, Chapel Hill, NC 27599-8700, USA.
authors.forename: Zachary Y
authors.initials: ZY
authors.lastname: Kerr
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Marshall
authors.forename: Herndon P
authors.initials: HP
authors.lastname: Harding
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Guskiewicz
mesh_terms: D001265:Athletic Injuries / Q000453:epidemiology*; D001924:Brain Concussion / Q000453:epidemiology*; D003863:Depression / Q000175:diagnosis / Q000453:epidemiology*; D005500:Follow-Up Studies; D005538:Football / Q000293:injuries*; D006801:Humans; D008297:Male; D011446:Prospective Studies; D012008:Recurrence; D012179:Retirement; D012307:Risk Factors; D057566:Self Report