title: The evolving relationship between premorbid intelligence and serious depression across the lifespan - A longitudinal study of 43,540 Swedish men.
abstract: An association between higher intelligence and lower probability of serious depression has previously been established. Yet, to our knowledge, no large prospective study has examined the relationship across the lifespan.
  
  
  
  A cohort of 49,321 Swedish men was followed from conscription in 1969-70 (age 18-20) through to 2008. Odds ratios (OR) for first time hospitalisation for depression (FTHD) were calculated in relation to intelligence for distinct time periods across the lifespan, while controlling for established risk factors for depression.
  
  
  
  There was a linear association between higher intelligence in youth and lower odds for FTHD during the entire follow-up period, 1973-2008. The association got progressively weaker across the lifespan. During 1973-80, one step down on the stanine scale was associated with an unadjusted increase in OR of 1.34 [95% confidence interval (CI) 1.26-1.42], adjusted OR 1.23 [1.15-1.32]; while, during 2001-2008, the ORs were less than half of the magnitude of the first period, unadjusted 1.14 [1.07-1.21], and adjusted 1.09 [1.01-1.17].
  
  
  
  The study includes men only, and the number of available places for in-patient care decreased during the follow-up period.
  
  
  
  For the first time, we have shown that the association between lower intelligence and depression decreases over time. The attenuation of the association in the adjusted models suggests a slower accumulation of depressogenic stressors among people with a higher IQ-score. Further exploration of intelligence's role in the etiology of depression across the lifespan is required in order to facilitate adequate diagnoses and ameliorating interventions.
authors.affiliation: Division of Psychology, Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden. Electronic address: emil.lager@stud.ki.se.
authors.forename: Emil
authors.initials: E
authors.lastname: Lager
authors.affiliation: Division of Psychology, Department of Clinical Neuroscience, Karolinska Institute, Stockholm, Sweden.
authors.forename: Bo
authors.initials: B
authors.lastname: Melin
authors.affiliation: Centre for Social Research on Alcohol and Drugs, Stockholm University, Stockholm, Sweden.
authors.forename: Tomas
authors.initials: T
authors.lastname: Hemmingsson
authors.affiliation: Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden.
authors.forename: Alma
authors.initials: A
authors.lastname: Sörberg Wallin
mesh_terms: D000328:Adult; D000368:Aged; D060825:Cognitive Dysfunction / Q000453:epidemiology; D003863:Depression / Q000453:epidemiology*; D003866:Depressive Disorder / Q000453:epidemiology*; D006801:Humans; D007360:Intelligence; D007361:Intelligence Tests; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
keywords: Cognitive epidemiology; Depression; IQ; Intelligence; Lifespan