Sibling Analysis of Adolescent Intelligence and Chronic Diseases in Older Adulthood

Abstract

We examined whether associations of adolescent intelligence with chronic diseases in adulthood are explained by socioeconomic factors, health behaviors, or common sources of variance in intelligence and chronic disease risk. A prospective cohort study (Wisconsin Longitudinal Study) of high school graduates andtheir siblings with intelligence assessed in adolescence and chronic diseases reported in adulthood (n = 10,168; mean age 53.9 and n = 9051; mean age 64.8 in two follow-ups). After adjustment for age and sex, greater intelligence was associated with lower risk of heart disease (odds ratio per 1 SD advantage in intelligence 0.93; 95% confidence interval 0.87-0.99), circulation problems (0.85; 0.79-0.92), stroke (0.80; 0.70-0.91), and diabetes (0.88; 0.81-0.95). Participants' risk of stroke and circulation problems also was predicted by their sibling's intelligence, suggesting potential common causes for intelligence and cerebrovascular diseases. Sibling analysis provided no support for shared family environment in explaining associations between intelligence and disease outcomes because between-families and within-siblings regression models were not different. Adjusting for common risk factors had little impact on these associations. In contrast, adjusting for adult socioeconomic status attenuated the associations by 25%-100% (66% on average). Multiple mechanisms may link intelligence with occurrence of chronic diseases of major public health importance.