Role of obesity and fat distribution in non-insulin-dependent diabetes mellitus in Mexican Americans and non-Hispanic whites.

Recent data have suggested that central obesity is related positively to the prevalence of non-insulin-dependent diabetes mellitus (NIDDM). We examined whether central obesity (measured by the ratio of subscapular to triceps skinfold) was predictive of NIDDM prevalence independently of overall obesity (measured by body mass index, BMI) in 1231 Mexican Americans and 939 non-Hispanic whites who participated in the San Antonio Heart Study, a population-based survey of diabetes and cardiovascular risk factors. Mexican Americans are characterized by higher rates of NIDDM, greater overall obesity, and more central body fat distribution than age-matched non-Hispanic whites. Using multiple logistic regression with age, ethnicity, BMI, and central obesity as covariates, overall obesity was positively associated with NIDDM prevalence in both sexes (P less than 0.001) but central obesity was related to NIDDM prevalence only in women. Our data suggest that the effect of centrality decreases at higher levels of centrality. While both BMI and centrality narrow the ethnic difference in NIDDM prevalence, Mexican Americans still have an increased risk of NIDDM (odds ratio = 2.33 in men and 1.80 in women), suggesting that other factors, possibly genetic, may also be important determinants of the ethnic differences in NIDDM prevalence.