Development of health-related waist circumference thresholds within BMI categories

To develop and cross-validate waist circumference (WC) thresholds within BMI categories. The utility of the derived values was compared with the single WC thresholds (women, 88 cm; men, 102 cm) recommended by NIH and Health Canada.

The sample included adults classified as normal weight (BMI = 18.5 to 24.9), overweight (BMI = 25 to 29.9), obese I (BMI = 30 to 34.9), and obese II+ (BMI > or = 35) from the Third U.S. National Health and Nutrition Examination Survey (NHANES III; n = 11,968) and the Canadian Heart Health Surveys (CHHS; n = 6286). Receiver operating characteristic curves were used to determine the optimal WC thresholds that predicted high risk of coronary events (top quintile of Framingham scores) within BMI categories using the NHANES III. The BMI-specific WC thresholds were cross-validated using the CHHS.

The optimal WC thresholds increased across BMI categories from 87 to 124 cm in men and from 79 to 115 cm in women. The validation study indicated improved sensitivity and specificity with the BMI-specific WC thresholds compared with the single thresholds.

Compared with the recommended WC thresholds, the BMI-specific values improved the identification of health risk. In normal weight, overweight, obese I, and obese II+ patients, WC cut-offs of 90, 100, 110, and 125 cm in men and 80, 90, 105, and 115 cm in women, respectively, can be used to identify those at increased risk.