We are grateful for Dr. Oda’s comments (1) on our recent report (2) regarding the usefulness of central obesity assessed by waist circumference in clinical risk assessment for type 2 diabetes in Japanese people. We agree with his opinion that the current Japanese cutoff points for central obesity (85 cm for men and 90 cm for women) are problematic and that there is ground for controversy.
We recalculated the risk of central obesity assessed by waist circumference for type 2 diabetes, applying the cutoff points proposed by Hara et al. (3) (85 or 83 cm for men and 78 or 73 cm for women) and Asian criteria of central obesity (90 for men and 80 cm for women). When applying Hara et al.’s cutoff points, the relative risks of central obesity for type 2 diabetes were 5.26 (95% CI 2.06–13.44) in men with an 83-cm waist circumference, 1.12 (0.51–2.48) in women with a 78-cm waist circumference, and 1.63 (0.68–3.91) in women with a 73-cm waist circumference. When applying the Asian criteria, the relative risks were 1.35 (0.59–3.06) in men and 1.53 (0.69–3.40) in women. We also plotted the receiver-operator characteristic curves for waist circumference to predict the presence of type 2 diabetes after 10 years, separately in men and women. According to the receiver-operator characteristic curves, waist circumference is a good predictor for occurrence of type 2 diabetes in men (84.5 cm: sensitivity 71.4% and specificity 59.6%) but is not a good predictor in women. There seem to be sex differences in the effect of central obesity assessed by waist circumference for occurrence of type 2 diabetes.
We are now analyzing the risk of metabolic syndrome for type 2 diabetes in Japanese patients using the same study population (in progress), and the results we have so far give us the impression that central obesity plus the accumulation of two or more risk factors (i.e., metabolic syndrome according to the International Diabetes Federation definition) is a stronger predictor for type 2 diabetes in both men and women than only central obesity without considering the presence of risk factors. The results also give us the impression that the current Japanese criteria of waist circumference is appropriate for men but that the appropriate cutoff point for women may be smaller than the current criteria.
Since there seem to be different impacts on the risk of central obesity for type 2 diabetes and the risk for cardiovascular events, further studies are needed to establish appropriate cutoff points of waist circumference in the Japanese population.
