Heritability of Body Mass Index Among Familial Generations.

Importance: Studies on the familial effects of body mass index (BMI) status have yielded a wide range of data on its heritability. Objective: To assess the heritability of obesity by measuring the association between the BMIs of fathers, mothers, and their offspring at the same age. Design, Setting, and Participants: This cohort study used data from population-wide mandatory medical screening before compulsory military service in Israel. The study included participants examined between January 1, 1986, and December 31, 2018, whose both parents had their BMI measurement taken at their own prerecruitment evaluation in the past. Data analysis was performed from May to December 2023. Main Outcomes and Measures: Spearman correlation coefficients were calculated for offsprings' BMI and their mothers', fathers', and midparental BMI percentile (the mean of the mothers' and fathers' BMI cohort- and sex-specific BMI percentile) to estimate heritability. Logistic regression models were applied to estimate the odds ratios (ORs) and 95% CIs of obesity compared with healthy BMI, according to parental BMI status. Results: A total of 447 883 offspring (235 105 male [52.5%]; mean [SD] age, 17.09 [0.34] years) with both parents enrolled and measured for BMI at 17 years of age were enrolled in the study, yielding a total study population of 1 343 649 individuals. Overall, the correlation between midparental BMI percentile at 17 years of age and the offspring's BMI at 17 years of age was moderate (ρ = 0.386). Among female offspring, maternal-offspring BMI correlation (ρ = 0.329) was somewhat higher than the paternal-offspring BMI correlation (ρ = 0.266). Among trios in which both parents had a healthy BMI, the prevalence of overweight or obesity in offspring was 15.4%; this proportion increased to 76.6% when both parents had obesity and decreased to 3.3% when both parents had severe underweight. Compared with healthy weight, maternal (OR, 4.96; 95% CI, 4.63-5.32), paternal (OR, 4.48; 95% CI, 4.26-4.72), and parental (OR, 6.44; 95% CI, 6.22-6.67) obesity (midparent BMI in the ≥95th percentile) at 17 years of age were associated with increased odds of obesity among offspring. Conclusions and Relevance: In this cohort study of military enrollees whose parents also underwent prerecruitment evaluations, the observed correlation between midparental and offspring BMI, coupled with a calculated narrow-sense heritability of 39%, suggested a substantive contribution of genetic factors to BMI variation at 17 years of age.