Abstract
BackgroundFew 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. MethodsThe 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 23years 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. Results & conclusionHigher 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=−0.03 p=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).
Highlights
25% of American adults are affected by mental health problems, with anxiety disorders and depression being the most common problems (American Psychiatric Association, 2015)
The present study examined the relationship between IQ in youth and four mental health outcomes taken at age 50
The results suggest that pre-morbid intelligence was significantly associated with mid-life mental health outcomes
Summary
25% of American adults are affected by mental health problems, with anxiety disorders and depression being the most common problems (American Psychiatric Association, 2015). Previous research has found that a SD increase of intelligence in youth tends to be associated with a 13% to 43% reduced risk of the above-mentioned mental health difficulties in adulthood (Gale, Deary et al, 2008; Gale et al, 2010; Koenen et al, 2007; Osler et al, 2007) When these studies adjusted for indicators of socio-economic status (i.e. parental occupation or education, or own education or income) the effect sizes in many cases were somewhat reduced; the majority of effects remained significant.
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