Title: Associations Of Body Fat Percentage, Body Mass Index, And All-cause Mortality: NHANES 1999-2006
Abstract: Limited studies have evaluated the collective associations of body fat percentage (BF%) and body mass index (BMI) with mortality. PURPOSE: To prospectively examine the collective associations of BF% and BMI with all-cause mortality in US adults (≥ 20 yr). METHODS: At baseline, participants’ (N = 16,137, 49.2% male) BF% was assessed by dual energy X-ray absorptiometry and BMI (kg/m2) was calculated from height and mass measurements. Self-reported physical activity, age, race, smoking status, fracture history, and pre-existing diabetes, COPD, renal disease, and cardiovascular disease were also assessed. Mortality status was obtained from National Health and Nutrition Examination Survey (NHANES) linked National Death Index data. Covariate adjusted and sex-stratified Cox proportional hazards models were used to estimate hazard ratios and 95% confidence intervals (HR [95% CI]) associated with mortality across quintiles (Q) of BF% and BMI (Q3 = reference). Analytical procedures for survey data were used to account for the complex design of NHANES. RESULTS: Over 242,791 person-years of follow-up (median follow-up = 15.9 yr) there were 3,880 deaths. In males, low and high BF% (Q1: 1.56 [1.20 - 2.03]; Q4: 1.36 [1.14 - 1.62]; Q5: 1.58 [1.32 - 1.90]) were associated with higher mortality without BMI adjustment. In females, only low BF% (Q1: 1.31 [1.02 - 1.69]) was associated with greater mortality without BMI adjustment. After BMI adjustment, only high BF% in males (Q4: 1.39 [1.15 - 1.69]; Q5: 1.56 [1.25 - 1.94) was associated with higher mortality, while BF% was not associated with mortality in females. In males, low and high BMI (Q1: 1.37 [1.12 - 1.69]; Q5: 1.37 [1.13 - 1.67]) were associated with higher mortality without BF% adjustment. In females, only low BMI (Q1: 1.27 [1.03 - 1.56]) was associated with greater mortality without BF% adjustment. After BF% adjustment, only low BMI in males (Q1: 1.42 [1.09 - 1.85]) was associated with higher mortality, while BMI was not associated with mortality in females. CONCLUSIONS: High BF% and low BMI, independent of BMI and BF%, respectively, were associated with higher mortality in males. Among females, BF% and BMI were not associated with mortality independent of BMI and BF%, respectively. Findings herein assist in explaining the complex relationships between BF%, BMI, and mortality.