title: Cognitive ability in early adulthood is associated with later suicide and suicide attempt: the role of risk factors over the life course.
abstract: BACKGROUND
  Cognitive ability/intelligence quotient (IQ) in youth has previously been associated with subsequent completed and attempted suicide, but little is known about the mechanisms underlying the associations. This study aims to assess the roles of various risk factors over the life course in explaining the observed relationships.
  
  
  METHODS
  The present investigation is a cohort study based on data on IQ test performance and covariates, recorded on 49 321 Swedish men conscripted in 1969-1970, at ages 18-20 years. Information on suicides and hospital admissions for suicide attempt up to the age of 57 years, childhood and adult socio-economic position, and adult family formation, was obtained from linkage to national registers.
  
  
  RESULTS
  Lower IQ was associated with increased risks of both suicide and suicide attempt during the 36 years of follow-up. The associations followed a dose-response pattern. They were attenuated by approximately 45% in models controlling for social background, mental ill-health, aspects of personality and behavior, adult socio-economic position and family formation. Based on one-unit decreases in IQ test performance on a nine-point scale, the hazard ratios between ages 35 and 57 years were: for suicide 1.19 [95% confidence interval (CI) 1.13-1.25], fully adjusted 1.10 (95% CI 1.04-1.18); and for suicide attempt 1.25 (95% CI 1.20-1.31), fully adjusted 1.14 (95% CI 1.09-1.20).
  
  
  CONCLUSIONS
  Cognitive ability was found to be associated with subsequent completed and attempted suicide. The associations were attenuated by 45% after controlling for risk factors measured over the life course. Psychiatric diagnosis, maladjustment and aspects of personality in young adulthood, and social circumstances in later adulthood, contributed in attenuating the associations.
authors.affiliation: Division of Occupational and Environmental Medicine, Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden. alma.sorberg@ki.se
authors.forename: A
authors.initials: A
authors.lastname: Sörberg
authors.forename: P
authors.initials: P
authors.lastname: Allebeck
authors.forename: B
authors.initials: B
authors.lastname: Melin
authors.forename: D
authors.initials: D
authors.lastname: Gunnell
authors.forename: T
authors.initials: T
authors.lastname: Hemmingsson
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D006801:Humans; D007360:Intelligence / Q000502:physiology*; D007361:Intelligence Tests; D008297:Male; D008505:Medical Staff, Hospital; D001523:Mental Disorders / Q000453:epidemiology; D008875:Middle Aged; D010551:Personality / Q000502:physiology; D012307:Risk Factors; D012917:Social Adjustment; D013405:Suicide; D013406:Suicide, Attempted; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult