title: Intelligence in youth and mental health at age 50.
abstract: BACKGROUND
  Few cognitive epidemiology studies on mental health have focused on the links between pre-morbid intelligence and self-reports of common mental disorders, such as depression, sleep difficulties, and mental health status. The current study examines these associations in 50-year-old adults.
  
  
  METHODS
  The study uses data from the 5793 participants in the National Longitudinal Survey of Youth 1979 cohort (NLSY-79) who responded to questions on mental health at age 50 and had IQ measured with the Armed Forces Qualification Test (AFQT) when they were aged between 15 and 23 years in 1980. Mental health outcomes were: life-time diagnosis of depression; the mental component score of the 12-item short-form Health Survey (SF-12); the 7-item Center for Epidemiological Studies Depression Scale (CES-D); and a summary measure of sleep difficulty.
  
  
  CONCLUSIONS
  Higher intelligence in youth is associated with a reduced risk of self-reported mental health problems at age 50, with age-at-first-interview and sex adjusted Bs as follows: CES-depression (B = - 0.16, C.I. - 0.19 to - 0.12,p< 0.001), sleep difficulties (B = - 0.11, C.I. - 0.13 to - 0.08,p< 0.001), and SF-12 mental health status (OR = 0.78, C.I. 0.72 to 0.85,p< 0.001;r= - 0.03p= 0.075). Conversely, intelligence in youth is linked with an increased risk of receiving a diagnosis of depression by the age of 50 (OR 1.11, C.I. 1.01 to 1.22,p= 0.024;r= 0.03,p= 0.109). No sex differences were observed in the associations. Adjusting for adult SES accounted for most of the association between IQ and the mental health outcomes, except for having reported a diagnosis of depression, in which case adjusting for adult SES led to an increase in the size of the positive association (OR = 1.32, C.I. 1.16 to 1.51,p< 0.001).
authors.affiliation: Center for Cognitive Ageing and Cognitive Epidemiology, Department of Psychology, University of Edinburgh, 7 George Square, Edinburgh, Scotland EH8 9JZ, United Kingdom.
authors.forename: Christina
authors.initials: C
authors.lastname: Wraw
authors.affiliation: Center for Cognitive Ageing and Cognitive Epidemiology, Department of Psychology, University of Edinburgh, 7 George Square, Edinburgh, Scotland EH8 9JZ, United Kingdom.
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Deary
authors.affiliation: MRC/CSO Social & Public Health Sciences Unit, 200 Renfield Street, University of Glasgow, Glasgow G2 3QB, United Kingdom.
authors.forename: Geoff
authors.initials: G
authors.lastname: Der
authors.affiliation: Center for Cognitive Ageing and Cognitive Epidemiology, Department of Psychology, University of Edinburgh, 7 George Square, Edinburgh, Scotland EH8 9JZ, United Kingdom; MRC Life Course Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton SO16 6YD, United Kingdom.
authors.forename: Catharine R
authors.initials: CR
authors.lastname: Gale
keywords: AFQT; Age 50; Cognitive epidemiology; Depression; Intelligence; Mental health; NLSY-79; SES; Sleep difficulties