The tails of the three anthropometric traits (BMI, height, and WHR) were defined as the upper 5th percentile (cases) and lower 5th percentile (controls) of the distribution stratified by sex and disease status after controlling for the following covariates: age, age2 and principal components for BMI; age and principal components for height; and age, age2, BMI and principal components for WHR. For the clinical obesity classes, cases were defined as BMI ≥25 kg/m2 for overweight, BMI ≥30 kg/m2 for obesity class I, BMI ≥35 kg/m2 for obesity class II, and BMI ≥40 kg/m2 for obesity class 3. Controls were subjects with BMI <25 kg/m2. A minimum of 30 cases and 30 controls for each study-specific stratum was required.
