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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.

Objective: We investigated the effects of head growth prenatally, during infancy, and during later periods of development on cognitive function at the ages of 4 and 8 years., Methods: We studied 633 term-born children from the Avon Longitudinal Study of Parents and Children cohort whose head circumference was measured at birth and at regular intervals thereafter. Their cognitive function was assessed with the Wechsler Preschool and Primary Scale of Intelligence at the age of 4 years and with the Wechsler Intelligence Scale for Children at the age of 8 years. Linear regression analysis was used to calculate postnatal head growth between successive time points, conditional on previous size, and to examine the relationship between head growth during different periods of development and later IQ., Results: When the influence of head growth was distinguished for different periods, only prenatal growth and growth during infancy were associated with subsequent IQ. At 4 years, after adjustment for parental characteristics, full-scale IQ increased an average of 2.41 points for each 1-SD increase in head circumference at birth and 1.97 points for each 1-SD increase in head growth during infancy, conditional on head size at birth. At 8 years, head circumference at birth was no longer associated with IQ, but head growth during infancy remained a significant predictor, with full-scale IQ increasing an average of 1.56 points for each 1-SD increase in growth., Conclusion: The brain volume a child achieves by the age of 1 year helps determine later intelligence. Growth in brain volume after infancy may not compensate for poorer earlier growth.