Maternal and offspring intelligence in relation to BMI across childhood and adolescence

Objective The present study tested the association between both mothers' and offspring's intelligence and offspring's body mass index (BMI) in youth. Method Participants were members of the National Longitudinal Survey of Youth 1979 (NLSY-79) Children and Young Adults cohort (n = 11,512) and their biological mothers who were members of the NLSY-79 (n = 4932). Offspring's IQ was measured with the Peabody Individual Achievement Test (PIAT). Mothers' IQ was measured with the Armed Forces Qualification Test (AFQT). A series of regression analyses tested the association between IQ and offspring's BMI by age group, while adjusting for pre-pregnancy BMI and family SES. The analyses were stratified by sex and ethnicity (non-Black and non-Hispanic, Black, and Hispanic). Results The following associations were observed in the fully adjusted analyses. For the non-Blacks and non-Hispanics, a SD increment in mothers' IQ was negatively associated with daughters' BMI across all age-groups, ranging from beta = -0.12 (95% CI -0.22 to -0.02, p = 0.021) in late childhood, to beta = -0.17 (95% C.I. -0.27 to -0.07, p = 0001), in early adolescence and a SD increment in boys' IQ was positively associated with their BMI in early adolescence beta = 0.09 (95% CI 0.01-0.18, p = 0.031). For Blacks, there was a non-linear relationship between mothers' IQ and daughters' BMI across childhood and between girls' IQ and BMI across adolescence. There was a positive association between mothers' IQ and sons' BMI in early adolescence (beta = 0.17, 95% CI 0.02-0.32, p = 0.030). For Hispanic boys, there was a positive IQ-BMI association in late childhood (beta = 0.19, 95% CI 0.05-0.33, p = 0.008) and early adolescence (beta = 0.17, 95% CI 0.04-0.31, p = 0.014). Conclusion Mothers' IQ and offspring's IQ were associated with offspring's BMI. The relationships varied in direction and strength across ethnicity, age group and sex. Obesity interventions may benefit from acknowledging the heterogeneous influence that intelligence has on childhood BMI.