Adolescent body mass index and cognitive performance: a nationwide study of 2.48 million Israeli adolescents.

Importance: The increased incidence of adolescent obesity over recent decades may be associated with lower cognitive performance than the expected potential.
Objective: We aimed to assess the association between adolescent body mass index (BMI) and cognitive function.
Design: A nationwide, cross-sectional, population-based study.
Setting: Pre-recruitment evaluation for military service during 1967-2018.
Participants: All Israeli-born adolescents, 1 459 522 males and 1 027 953 females aged 16 to ≤20 years.
Exposures: Weight and height were measured to calculate BMI.
Main Outcome: Cognitive performance was assessed by using a validated intelligence-quotient-equivalent test and was standardized to the year- and sex-Z-score. For 445 385 persons, parental cognitive scores could be identified. Multinomial logistic regression models were applied.
Results: Among male adolescents with severe obesity, 29.4% achieved a cognitive score below the 25th percentile, compared with 17.7% among their normal-weight (50th-84th percentile) counterparts. A J-shaped relation was observed between BMI and the odds ratio (OR) for a low cognitive score among male adolescents: underweight, 1.45 (1.43-1.48); overweight, 1.13 (1.12-1.15); mild obesity, 1.36 (1.33-1.39); and severe obesity, 1.58 (1.52-1.64). Similar findings were observed in females. For both sexes, point estimates were overall consistent in models adjusted for sociodemographic confounders, coexisting morbidities, and parental cognitive scores. Examinees with abnormal BMI had higher ORs for a lower-than-expected cognitive score, based on their parents' data as adolescents, in a manner that depends on obesity severity.
Conclusion and Relevance: Obesity, is associated with increased odds for a lower cognitive performance, and the inability to fully achieve cognitive potential, regardless of sociodemographic background.
Competing Interests: Conflict of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
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