Cut Points of Waist Circumference: Response to Sone and Colleagues

Sone and colleagues (1,2) adopted Japanese criteria of abdominal obesity (waist circumference ≥85 cm in men and ≥90 cm in women) for the diagnosis of metabolic syndrome. These Japanese criteria of abdominal obesity were proposed by the Examination Committee of Criteria for Obesity Disease in Japan set up by the Japan Society for the Study of Obesity (3). They proposed waist circumferences of 85 cm in men and 90 cm in women as equivalent values for visceral fat area (VFA) of 100 cm². However, these cut points of waist circumference resulted from the inappropriate presupposition that VFA is linearly proportional to waist circumference. They determined the values by linear regression lines without revealing the sensitivities and specificities of these cut points. In fact, the dots in their VFA–waist circumference graphs were not scattered along linear lines, though VFA and waist circumference correlated well (3). If they had determined the cut points of waist circumference by receiver operating characteristic curves as they did to determine the cut points of BMI and VFA and determined the cut points of VFA separately by sex, the cut points of waist circumference might have been equivalent to Asian criteria (≥90 cm in men and ≥80 cm in women). For example, Shiwaku et al. (4) reported that optimal cut points of waist circumference were 82 cm for men and 73 cm for women in Japan. If the Examination Committee calculated areas under receiver operating characteristic curves, waist circumference might reveal to be a poor discriminator of VFA especially in women. After all, waist circumference is a marker of abdominal (central) obesity not of visceral obesity, which is assessed by VFA using computer tomography scanning, exposing subjects to X-ray irradiation. Therefore, Sone et al. should reanalyze their data using Asian criteria of waist circumference (≥90 cm in men and ≥80 cm in women) before reaching conclusions on the prognostic significance of metabolic syndrome defined with both National Cholesterol Education Panel (1) and International Diabetes Federation (2) criteria in Asian diabetic patients.