Addition of Cardiorespiratory Fitness Within an Obesity Risk Classification Model Identifies Men at Increased Risk of All-Cause Mortality

T. Alexander Ricketts, Xuemei Sui, Carl J. Lavie, Steven N. Blair, Robert Ross

Guidelines for identification of obesity-related risk stratify disease risk using specific combinations of body mass index and waist circumference. Whether the addition of cardiorespiratory fitness, an independent predictor of disease risk, provides better risk prediction of all-cause mortality within current body mass index and waist circumference categories is unknown. To determine whether the addition of cardiorespiratory fitness improves prediction of all-cause mortality risk classified by the combination of body mass index and waist circumference. We performed a prospective observational study using data from the Aerobics Center Longitudinal Study (ACLS). A total of 31,267 men (mean age 43.9 [SD, 9.4] years) who completed a baseline medical examination during 1974-2002. The main outcome measure was all-cause mortality. Participants were grouped using body mass index- and waist circumference-specific threshold combinations: Normal body mass index: 18.5-24.9 kg/m(2), waist circumference threshold of 90 cm; overweight body mass index: 25.0-29.9 kg/m(2), waist circumference threshold of 100 cm, and obese body mass index: 30.0-34.9 kg/m(2), waist circumference threshold of 110 cm. Participants were classified using cardiorespiratory fitness as unfit or fit, where unfit was the lowest fifth of the age-specified distribution of maximal exercise test time on treadmill among the entire ACLS population. 1,399 deaths occurred over a follow-up of 14.1 ± 7.4 years, for a total of 439, 991 person-years of observation. Males who were unfit and normal body mass index with waist circumference <90 cm and ≥90 cm had 95% (1.95, 1.34-2.83) [Hazard ratio, 95% confidence interval] and 163% (2.63, 1.58-4.40) higher mortality risk than males who were fit, respectively (p<.05). Males who were unfit and overweight had 41% (1.41, 1.04-1.90) higher mortality risk with a waist circumference <100 cm (p<.05), but were at no greater risk (1.30, 0.92-1.84) if their waist circumference was ≥100 cm (p=.14). Males who were unfit and obese were not at increased mortality risk (1.37, 0.90-2.09) with a waist circumference <110 cm (p=.14), but were at 111% (2.11, 1.31-3.42) increased risk with a waist circumference ≥110 cm (p<.05). For most of the body mass index and waist circumference categories, inclusion of cardiorespiratory fitness allowed for improved identification of males at increased mortality risk.