OBJECTIVE: To examine whether the association between childhood IQ and later mortality risk was explained by early developmental advantages or mediated by adult sociodemographic factors and health behaviors.

PARTICIPANTS AND METHODS: Participants were 10 620 men and women from the 1958 British Birth Cohort Study whose IQ was assessed at the age of 11 years and who were followed up to age 46. Childhood covariates included birth weight, childhood height at 11 years of age, problem behaviors, father's occupational class, parents' interest in child's education, family size, and family difficulties. Adult risk factors were assessed at ages 23, 33, and 42 years, and they included education, occupational class, marital status, smoking, BMI, alcohol use, and psychosomatic symptoms.

RESULTS: Between ages 23 and 46 years, 192 participants died. Higher childhood IQ was related to lower mortality risk (standardized odds ratio [OR]: 0.80 [95% confidence interval (CI): 0.69–0.93]) with no gender differences (OR: 0.81 [95% CI: 0.67–0.98] [men] and 0.79 [95% CI: 0.63–0.98] [women]). Adjusting for parents' interest in child's education attenuated the IQ-mortality association by 15% to 20%, and adult education and psychosomatic symptoms both attenuated the association by 25%. Other covariates were less influential.

CONCLUSIONS: In a cohort of British men and women, the most important explanatory factors for the lower mortality rate among individuals with high IQ were parental interest in child's education, high adult educational level, and low prevalence of psychosomatic symptoms. However, common sociodemographic risk factors and health behaviors may not be sufficient to explain the association between IQ and early mortality completely.

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