Racial differences in rates of type 2 diabetes in American women: how much is due to differences in overall adiposity?

BACKGROUND: Although the rates of type 2 diabetes attributable to obesity have been documented by numerous studies, little attention has been paid to an important question of, "what fraction of the differences in rates of diabetes between high-risk and low-risk women is due to their differences in prevalence of obesity? This study aimed, therefore, to determine how much of the relative difference in the rates of type 2 diabetes between high-risk non-Hispanic Black and low-risk non-Hispanic White American women can be attributed to differences in overall adiposity.
METHODS: Data (n = 1,222) from the Third National Health and Nutrition Examination Survey (1988-94) was used in this investigation. Obesity was defined as body mass index of 30 kg/m2 or more. Estimates of population attributable risks and relative attributable risks were derived using multiple logistic regression models, adjusting for age, smoking and alcohol intake.
RESULTS: There were within and between population differences in the impact of obesity on diabetes. The impact of obesity on diabetes as measured by odds ratio and population attributable risk was greater for White women compared to Black women. Obesity was independently associated with a 4-fold (OR = 4.43; 95% CI: 2.65, 7.44) and almost a 2-fold (OR = 1.85; 95% CI: 0.99, 3.47) increased risks of diabetes for White and Black women, respectively. Being Black was associated with an almost 2-fold (OR = 1.86; 95% CI: 1.22, 2.82) increased risk of diabetes relative to White. The population attributable risks of diabetes due to obesity were 49.9% and 28% in Whites and Blacks, respectively. Over one-third (39%) of the difference in rates of diabetes between Black and White women was attributable to differences in the prevalence of overall obesity, adjusting for age, smoking and alcohol consumption.
CONCLUSIONS: The result of this study indicating that obesity is a significant factor in explaining the higher prevalence of diabetes among Black women has public health relevance. Since obesity is a preventable and an avoidable risk factor for type 2 diabetes in all populations, the result of this investigation presents a compelling reason to emphasize public health measures to educate women on the need to reduce weight, particularly the high-risk black American women.