Cardiorespiratory Fitness within an Obesity Risk Classification Model Identifies Men at Increased Risk of Mortality

Abstract

Guidelines for identification of obesity-related risk stratify disease risk using specific combinations of body mass index (BMI) and waist circumference (WC). Whether the addition of cardiorespiratory fitness (CRF), an independent predictor of disease risk, provides better risk prediction of all-cause mortality within current BMI and WC categories is unknown. PURPOSE: To determine whether the addition of CRF improves prediction of all-cause mortality risk classified by established categorization of BMI and WC. METHODS: Prospective observational data from the Aerobics Center Longitudinal Study (ACLS). A total of 31,267 men (mean (SD) age 43.9 (9.4) years completed a baseline medical examination during 1974-2002. Participants were grouped according to the following BMI- and WC-specific threshold combinations: Normal BMI of 18.5-24.9 kg/m2, WC threshold of 90 cm; overweight BMI of 25.0-29.9 kg/m2, WC threshold of 100 cm, and obese BMI of 30.0-34.9 kg/m2, WC threshold of 110 cm. Participants were classified by CRF as unfit or fit. Unfit was defined as the lowest fifth of the age-specified distribution of maximal exercise test time on treadmill among the entire ACLS population. The main outcome measure was all-cause mortality. RESULTS: 1,399 deaths occurred over an average length of follow-up of 14.1 ± 7.4 years, for a total of 439, 991 person-years of observation. Males who were unfit and normal BMI with WC<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 WC <100 cm (p<.05), but were at no greater risk (1.30, 0.92-1.84) if their WC 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 WC <110 cm (p=.14), but were at 111% (2.11, 1.31-3.42) increased risk with a WC ≥110 cm (p<.05). CONCLUSIONS: For most of the BMI and WC categories, inclusion of CRF allowed for improved identification of males at increased mortality risk.