Thigh Circumference and Diabetes: Obesity as a Potential Effect Modifier

BACKGROUND Thigh circumference is associated with diabetes risk; however, the role of obesity as a potential effect modifier has not been well studied. METHODS We examined the association between thigh circumference and diabetes in a cross-sectional study of 384 612 Koreans aged 30 to 79 years. The association between diabetes and thigh circumference in relation to body mass index (BMI) was analyzed among 315 628 participants, using multivariate logistic regression. Thigh circumference was categorized into 9 percentile categories-namely, the 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97.5th percentiles-and the 50th percentile was used as the reference value for thigh circumference. Separate analyses were performed for men and women. RESULTS The association of thigh circumference with diabetes showed contradictory patterns before and after adjustment for BMI and waist circumference. Small thigh circumference was associated with greater risk of diabetes among men and women. This relationship was stronger among participants younger than 50 years, although age was not a significant effect modifier. BMI was a significant effect modifier among men with a BMI of less than 25 kg/m(2). Among women, diabetes risk increased with smaller thigh circumference. CONCLUSIONS Small thigh circumference was associated with diabetes, and this association was stronger among participants with a BMI of less than 25 kg/m(2). Thigh circumference might be a useful diabetes marker in lean populations.