People born in the U.S. have higher body mass index (BMI) and a greater risk of obesity than those born abroad, according to a large New York-based study. The data also revealed that African ancestry is associated with the likelihood of being obese in U.S.-born women.
The research, “The role of country of birth, and genetic and self-identified ancestry, in obesity susceptibility among African and Hispanic Americans,” was published in The American Journal of Clinical Nutrition.
The prevalence of obesity differs across populations of different ancestry in the U.S., which may be explained by distinct lifestyle and cultural practices, as well by specificities in genetic ancestry and socioeconomic status.
Self-reported ancestry differs from genetic ancestry in that it is based on self-identification with a certain ancestral group, and represents one’s lifestyle, cultural norms and habits, and healthcare access, among other aspects.
The genetic mix of migrant populations in the U.S. enables the differentiation between genetic and self-reported ancestry and their contributions to disease susceptibility. For instance, data have shown that, among people who self-identify as African Americans, those with a higher proportion of West African ancestry have higher BMI — particularly women.
The scientists evaluated the extent to which genetic and self-reported ancestry, as well as the country of birth, contribute to BMI and obesity risk among participants who self-identify as African Americans and Hispanic/Latinos.
Their analysis used the Mount Sinai BioMe Biobank, which includes data from the patient population at Mount Sinai Hospital, in New York. The participants are predominantly of African American (24%), Hispanic/Latino (35%), and European American ancestry (32%).
The analysis included a total of 13,937 adults (mean age 51.3 years), 6,398 of whom self-reported as African Americans and 7,569 as Hispanic/Latinos. African Americans showed higher BMI (30.3 vs. 29.5; women showing a greater difference) and were two to three years younger than Hispanic/Latinos.
Among women, the prevalence of obesity was greater in African Americans (50.8%) than in Hispanic/Latinas (42.7%). In contrast, men showed no difference.
African Americans were twice as likely to be born in the U.S. than Hispanic/Latinos (82% vs 41%). Among the 1,144 non-U.S.-born participants who self-reported as African Americans, those born in Jamaica represented the greatest proportion (24.6%). In turn, most of the 4,483 non-U.S.-born participants who self-reported as Hispanic/Latinos were born in Puerto Rico (49.8%) or the Dominican Republic (36.9%).
The proportion of African ancestry (PAA) was significantly greater among people self-reporting as African American (median 87%) than among those self-reporting as Hispanic/Latinos (25%), though with wide variability.
A subsequent analysis showed that higher PAA, Hispanic/Latino ancestry, being born in the U.S., age, and sex were all linked with higher BMI.
Specifically, country of birth and genetic ancestry were significantly associated with BMI in women. Those born in the U.S. had a BMI 99% higher than those born elsewhere. Every 10% increase in PAA led to a 0.29 increase in BMI, which is equivalent to 0.74 kg for a woman 1.6-meters (5 feet, 7 inches) tall.
The likelihood of being obese was 55% higher in women born in the U.S. Among these women, every 10% increase in PAA correlated with a 10% higher risk of obesity.
Also in women, self-reported Hispanic/Latino ancestry was associated with a 0.61 higher BMI than African American ancestry. However, accounting for PAA and age made the contribution of self-reported ancestry no longer significant, because this effect was driven by a lower PAA and higher frequency of being born abroad in Hispanic/Latinas.
Every 10-year increase in age resulted in a 0.30 increase in BMI. Also, the association between PAA and higher BMI was significantly more pronounced among U.S.-born than among non-U.S.-born women.
In contrast, country of birth was the only factor significantly influencing BMI and obesity. Men born in the U.S. showed a 33% higher BMI — approximately 4.1 kg for a man 1.75-meters (5 feet, 7 inches) tall — and a 47% greater risk of obesity than those not born in the country.
“Being US-born is associated with a substantially higher BMI and risk of obesity in both men and women,” the scientists wrote. Also, “genetic ancestry, but not self-reported ancestry, is associated with obesity susceptibility, but only among US-born women,” they added.