Waist circumference and body composition in relation to all-cause mortality in middle-aged men and women

OBJECTIVE: Waist circumference is directly related to all-cause mortality when adjusted for body mass index (BMI). Body fat and fat-free body mass, when mutually adjusted, show with increasing values an increasing and decreasing relation to all-cause mortality. We investigated the association of waist circumference and body composition ( body fat and fat-free mass), mutually adjusted, to all-cause mortality. DESIGN: A Danish prospective cohort study with a median follow-up period of 5.8 y. SUBJECTS: In all, 27 178 men and 29 875 women, born in Denmark, aged 50-64 y, and without diagnosis of cancer at the time of invitation. MEASUREMENTS: Waist circumference and body composition estimated from impedance measurements. Cox's regression models were used to estimate the mortality rate ratios (RR). RESULTS: Waist circumference was strongly associated with all-cause mortality after adjustment for body composition; the mortality RR was 1.36 (95% confidence intervals (CI): 1.22-1.52) times higher per 10% larger waist circumference among men and 1.30 (95% CI: 1.17-1.44) times higher among women. Adjustment for waist circumference eliminated the association between high values of the body fat mass index (BFMI) and all-cause mortality. The association between fat-free mass index (FFMI) and mortality remained unaltered. CONCLUSION: Waist circumference accounted for the mortality risk associated with excess body fat and not fat-free mass. Waist circumference remained strongly and directly associated with all-cause mortality when adjusted for total body fat in middle-aged men and women, suggesting that the increased mortality risk related to excess body fat is mainly due to abdominal adiposity.