Relative importance and joint association of overall obesity and body fat distribution as predictor of mortality risk
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Morbidity and mortality risks are decreased alongside elevations in lower-body adiposity and/or muscle mass, underlying the reversal of the risk association between body mass index (BMI) and hip circumference once these measures are adjusted for abdominal obesity. A total of 5799 men and 6429 women aged 30-102 years enrolled in the third National Health and Nutrition Examination Survey were studied in order to compare the relative importance and joint association of overall obesity and body fat distribution in predicting risk of mortality. During the 12-year follow-up, 1188 men and 925 women died. Multivariable-adjusted analyses revealed that waist-to-thigh ratio (WTR; thigh circumference being a surrogate for subcutaneous adipose tissue, skeletal muscle in the lower body, or both) in both sexes and waist-to-hip ratio (WHR) in women were positively associated with mortality in middle-aged adults, while BMI and waist circumference (WC) exhibited U- or J-shaped associations. Among normal weight and obese adults, risk of mortality increased with a higher WHR and WTR. In adults aged ≥65 years, a higher BMI in both sexes and WC in men were associated with increased survival, whilst remaining measures of body fat distribution exhibited either no relation or an inverse relation with mortality. These results suggest that body fat distribution ratios are strongly and positively associated with mortality and offer additional prognostic information beyond BMI and WC.
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