The relationship between obesity and cognitive performance in children: A longitudinal study

Background: The relationship between obesity and academic outcomes remains unclear. We evaluated the association between obesity and cognitive performance in US children. Methods: We analyzed two nationally representative prospective cohorts of children in the 1979 National Longitudinal Survey of Youth, ages 2 through 8 at baseline and followed for 6 years, from 1988 to 1994 (cohort 1, n=2672) and 1994 to 2000 (cohort 2, n=1991). The main exposure variable was obesity (defined as never obese, became obese, always obese, and became nonobese). The main outcomes were standardized scores on four cognitive assessments. Univariate regression analyses of test scores on obesity were performed. Fixed-effects regression models, controlling for measured and unmeasured time-invariant confounders, were additionally adjusted for time-variant confounders to analyze the impact of change in obesity status on change in test scores. Results: Unadjusted analyses revealed a significant association between obesity and Peabody Individual Achievement Test (PIAT) scores. In cohort 1, always obese children had lower PIAT math scores than never obese children (β=-7.48; p<0.05). Always obese boys had lower PIAT math scores than those who were never obese (β=-16.45; p<0.01). In cohort 2, PIAT math scores were lower in the became obese category than the never obese category (β=-4.10; p<0.05). Always obese girls had lower PIAT reading scores than those who were never obese (β=-11.28; p<0.01). Fixed-effects models additionally adjusted for Home Observation Measurement of the Environment, Short Form score and height percentile showed no significant relationship between obesity and test scores in either cohort. Conclusion: Childhood obesity is unlikely to be causally related to cognitive performance.