Obesity Epidemiology

72 STUDY DESIGNS AND MEASUREMENTS(P < .01). Hip circumference adjusted for BMI and WC was associated with these riskfactors in the opposite direction. In a recent prospective analysis of participants in theHPFS, men whose WC had increased 14.6 cm or more after controlling for weight gainhad 1.7 (95% CI: 1.0 to 2.8) times the risk of diabetes compared with men with a stableWC. In contrast, men who lost more than 4.1 cm in hip girth had 1.5 (95% CI: 1.0 to 2.3)times the risk of diabetes compared with men with a stable hip circumference. 125 Theseresults suggest that increases or decreases in waist and hip circumferences reflect changesin different aspects of body composition, with varying implications for disease risk.As previously discussed, differential loss of muscle associated with aging makes BMIa less valid measure of body fatness in older adults. However, WC has been shown to bea good predictor of adiposity, especially central obesity, in the elderly. In the HPFS, overalladiposity measured by BMI was a more important indicator of risk of CHD amongmen younger than 65 years of age, whereas central obesity measured by WC and WHRappeared to be a stronger predictor of risk than BMI among men older than 65 years. 126These findings underscore the importance of measuring both overall adiposity and fatdistribution in epidemiologic studies of obesity.It remains controversial whether fat distribution should be routinely measured in clinicalpractice. 121 There is substantial evidence that fat distribution measurements have addedvalue beyond BMI in predicting morbidity and mortality among patients who are of normalweight or moderately overweight (see Chapters 8 to 11). Thus fat distribution shouldprovide additional value in risk assessment of obesity-related disease risk, 127 although suchmeasurements may be unnecessary for morbidly obese patients (BMI ≥ 35 kg/m 2 ).There are several rationales for the use of WC instead of WHR in practice. First,measuring WC is simpler than measuring WHR and has fewer measurement errors. Second,the association between WC and disease risk is easier to explain than is that forWHR (previously discussed). Third, several studies have suggested a stronger associationbetween WC and the risk of developing health conditions, such as cardiovascular diseaseand type 2 diabetes, although the results are not entirely consistent. 128 A statement bythe National Institutes of Health and the North American Association for the Study ofObesity concluded that WHR provides no advantage over WC alone. 129 RecommendedWC cutoffs were 40 in. (102 cm) for men and 35 in. (88 cm) for women (correspondingcut-points for WHR of 0.95 for men and 0.88 for women). However, these cut-pointsare arbitrary, as the relationship between increased WC and elevated metabolic andcardiovascular risk appears to be linear. Also, the RR of chronic disease associatedwith central obesity varies across different age and ethnic groups. Nonetheless, thesecutoff have been used in the National Cholesterol Education Program Adult TreatmentPanel III (NCEP ATP III) 4 guidelines as a diagnostic criteria for metabolic syndrome.As with BMI, the risk of diabetes and cardiovascular disease appears to be higher ata lower WC in Asians than in whites. 130 Thus, the use of lower WC cutoff points hasbeen proposed for Asians (e.g., >80 cm for women and >90 cm for men). 112 Recently,the International Diabetes Federation (IDF) proposed a new definition of metabolic syndromethat includes central obesity as a prerequisite for diagnosis along with gender- andethnicity-specific cut-points for WC. 5 However, these varying cut-points, which remaincontroversial, complicate the definition and clinical diagnosis of metabolic syndrome indifferent populations.Validity of Self-measured Waist and Hip CircumferencesIn large epidemiologic surveys conducted by mail, participants are asked to measure andreport body circumferences. Although participants (especially obese adults) tended to