Racial Differences in Abdominal Adiposity

A major U.S. public health goal is to significantly reduce racial disparities in health. One area of study has been the effect of racial differences upon the prevalence of generalized obesity (body mass index, or BMI, kg/m² of 30 or above). On February 9, First Lady Michelle Obama told the U.S. Conference of Mayors in Alexandria, VA, that one-third of today’s children eventually will suffer from diabetes and, in the African-American and Latino communities, the proportion will be almost half. The prevalence of obesity among adults reported in the 2003-2004 National Health and Nutrition Examination Survey (NHANES) was 30.6% among white Americans, but 45% among African-American men and women (JAMA 2006; 295:1549).These differences by race have also been reported among children and adolescents.

Researchers at the Pennington Biomedical Research Center, Baton Rouge, LA, examined specific body depot areas as a way to determine if there were differences in abdominal visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) among 1,967 white and African-American adults 18 to 94 years of age. VAT, in particular, has been identified as a marker of health risk, with potentially greater specificity than total fat mass or generalized obesity.

The study was part of the Pennington Center Longitudinal Study, an ongoing investigation among volunteers of obesity, lifestyle, and the development of common chronic diseases, such as type 2 diabetes, cardiovascular disease, and of premature death (Am J Clin Nutr 2010; 91:7).The study group included 790 white women, 435 African American women, 606 white men, and 136 African-American men.

Study methods

During the volunteer’s first visit to the screening site, a nurse measured height in duplicate by using a wall-mounted stadiometer and weight in duplicate by using a digital scale. BMI was calculated, and total body fat mass (kg) was estimated by DEXA with a whole-body scanner. Then computed tomographic scans were performed with the participant lying supine with arms over his or her head. Age was computed from birth and observation dates. Menopausal status (premenopausal/postmenopausal) was determined by age and responses to questions about reproductive health.

Results

African-American men and women were significantly younger than were white men and women, respectively. While racial differences in height were not significant, African-American women had significantly greater body weight, higher BMIs and total body fat compared with white women, and white men had significantly greater total body fat compared with African- American men.

Even after adjustment for covariates, abdominal visceral adipose tissue (VAT) was significantly higher in white men and women than in African-American men and women. Abdominal SAT was significantly higher in white men compared with African-American men; however, after adjustment for covariates, it was lower among white men compared with African American men. Abdominal SAT was significantly higher in African American women compared with white women (from the perspective of the present study, at least as these populations might appear in Baton Rouge, LA).

The results of this study, believed to be the largest yet published that examines racial differences in abdominal depot-specific body fat, both support and contradict the results of earlier studies, according to the authors. Most previous studies have also reporter lower amounts of abdominal VAT in African-American men compared with white men; however, previous studies of racial differences in abdominal VAT among African-American and white women have produced mixed results. This study confirmed the results of six prior studies showing significantly lower VAT among African-American women compared with white women.

The finding that African-Americans have lower amounts of abdominal VAT yet higher mortality rates from diabetes, cardiovascular disease and cancer than white Americans is a paradox, according to the authors. African-American women had higher amounts of abdominal SAT than did their white women counterparts and although white men had higher abdominal SAT than did African-American men, the differences reversed after adjustment for total body fat. An independent effect of race appears to exist for abdominal SAT: African-American men and women had higher amounts of SAT than did white men and women, after adjustment for total body fatness.

According to the authors, the results of this study highlight the heterogeneity of human body fat distribution across racial groups, and suggest the need for more research to determine the immediate and long-term health consequences of the observed racial differences in abdominal depot-specific body fatness.