In adult populations, it is recognized widely that waist circumference (WC) predicts health risk beyond that predicted by BMI alone; current recommendations for adults are that a combination of BMI and WC be used to classify obesity-related health risk. For children and adolescents, however, little is known about the combined influence of BMI and WC on health outcomes. The objectives of this study were to determine whether BMI and WC predict coronary artery disease (CAD) risk factors independently for children and adolescents and to assess the clinical utility of using WC in combination with BMI to identify CAD risk.
Subjects included 2597 black and white, 5- to 18-year-old, male and female youths. Outcome measures included 7 CAD risk factors. In the first analysis step, BMI and WC were used as continuous variables to predict CAD risk factors. In the second analysis step, participants were placed into normal-weight, overweight, and obese BMI categories and, within each BMI category, CAD risk factors were compared for groups with low and high WC values.
When BMI and WC were included in the same regression model to predict CAD risk factors, the added variance above that predicted by BMI or WC alone was minimal, which indicated that BMI and WC did not have independent effects on the risk factors. For example, for systolic blood pressure, BMI alone explained 7.3% of the variance, WC alone explained 7.7% of the variance, and the combination of BMI and WC explained 8.1% of the variance. When BMI and WC values were categorized with a threshold approach, WC provided information on CAD risk beyond that provided by BMI alone, particularly when the categories were used to predict elevated CAD risk factor levels. For instance, in the overweight BMI category, the high-WC group was approximately 2 times more likely to have high triglyceride levels, high insulin levels, and the metabolic syndrome, compared with the low-WC group.
These findings provide some evidence that a combination of BMI and WC should be used in clinical settings to evaluate the presence of elevated health risk among children and adolescents.