role of country of birth, and genetic and self-identified ancestry, in obesity susceptibility among African and Hispanic Americans.

Background African Americans (AAs) and Hispanic/Latinos (HLs) have higher risk of obesity than European Americans, possibly due to differences in environment and lifestyle, but also reflecting differences in genetic background. Objective To gain insight into factors contributing to BMI (in kg/m²) and obesity risk (BMI ≥ 30) among ancestry groups, we investigate the role of self-reported ancestry, proportion of genetic African ancestry, and country of birth in 6368 self-identified AA and 7569 HL participants of the New York–based Bio Me Biobank. Methods AAs and HLs are admixed populations that trace their genetic ancestry to the Americas, Africa, and Europe. The proportion of African ancestry (PAA), quantified using ADMIXTURE, was higher among self-reported AA (median: 87%; IQR: 79–92%) than among HL (26%; 15–41%) participants. Approximately 18% of AA and 59% of HL participants were non–US-born. Results Because of significant differences between sexes (P _{PAA*sex interaction} = 4.8 × 10⁻²²), we considered women and men separately. Among women, country of birth and genetic ancestry contributed independently to BMI. US-born women had a BMI 1.99 higher than those born abroad (P  = 7.7 × 10⁻²⁵). Every 10% increase in PAA was associated with a BMI 0.29 higher (P  = 7.1 × 10⁻¹⁰). After accounting for PAA and country of birth, the contribution of self-reported ancestry was small (P  = 0.046). The contribution of PAA to higher BMI was significantly more pronounced among US-born (0.35/10%PAA, P  = 0.003) than among non–US-born (0.26/10%PAA, P  = 0.01) women (P _{PAA*sex interaction} = 0.004). In contrast, among men, only US-born status influenced BMI. US-born men had a BMI 1.33 higher than non–US-born men, whereas PAA and self-reported ancestry were not associated with BMI. Associations with obesity risk were similar to those observed for BMI. Conclusions Being US-born is associated with a substantially higher BMI and risk of obesity in both men and women. Genetic ancestry, but not self-reported ancestry, is associated with obesity susceptibility, but only among US-born women in this New York–based population. [ABSTRACT FROM AUTHOR]