Obesity has long been a rising problem across the United States, and currently 35.7% of the adult population is obese, according to the Centers for Disease Control. Among all groups, non-Hispanic blacks have the highest obesity rates (49.5%); the next highest are Mexican Americans (40.4%), all Hispanics (39.1%) and non-Hispanic whites (34.3%).

A 2012 study published in the American Journal of Epidemiology suggests that the biological risks associated with obesity may not be uniform across racial groups. Several other studies, including one by the National Institutes of Health and the National Center for Health Statistics, present similar findings, but this is among the first studies to examine a large enough cohort to make valid comparisons between black and white populations of similar characteristics.

The 2012 study, “Obesity and All-Cause Mortality Among Black Adults and White Adults,” surveyed 76,614 adults ages 40 to 79 in 12 southeastern states — which have a largely low-income population — via in-person interviews and mail-in questionnaires seeking to understand the effect of race on obesity and mortality. The researchers were affiliated with the International Epidemiology Institute, Vanderbilt University Medical Center and Vanderbilt-Ingram Cancer Center, and Meharry Medical College.

The study’s findings include:

• African-American individuals with a body mass index between 30 and 34.9 actually have a lower risk of mortality than do ideal target weight cohorts of the same race. This diverges from patterns in white populations, where individuals with an elevated BMI (body mass index) have a 50% higher risk of mortality.
• Obesity, which is a BMI of greater than 30, was common in all four race and gender groups, but highest among black women (58%).
• For both black men and black women, the BMI with the lowest hazard ratio was between 30 and 34.9. Blacks at highest risk of death were those with a BMI less than 20.
• For cause of death, the most pronounced differences between blacks and whites were seen in cardiovascular disease, where whites in obesity classes II and III claimed a two-fold increase.
• Neither age nor gender significantly altered mortality rates among obese black populations, whereas death rates increased for obese white populations when they were 55 and older.
• Among obese blacks and whites, mortality risks tended to be lower among those with lower socioeconomic status. Those with limited education (less than 12 years) also proved to have a lower mortality risk.
• For all sex and race cohorts, except for white males, underweight individuals experience significantly higher mortality than those who were of normal weight.
• An American Cancer Society’s Cancer Prevention Study II, which included 12,000 blacks, also found a significantly increased mortality risk among whites with extreme obesity, but the association was not significant among black females and males. The National Institutes of Health also did a study that included 20,200 blacks; in that study, associations between BMI and mortality were also lower among blacks than whites.

The researchers do not offer any theories as to why obesity may affect whites and blacks differently. Socioeconomic differences have been postulated, but the study’s authors said this “seems unlikely to account for elevated BMI as a risk factor only for whites in this study because income and education distributions were fairly similar between black participants and white participants.”

Related research: For a more detailed view of trends and rates over time, see the 2012 study “Prevalence of Obesity and Trends in the Distribution of Body Mass Index Among U.S. Adults, 1999-2010” published in the Journal of the American Medical Association.

Tags: African-American, obesity