Addition of Cardiorespiratory Fitness Within an Obesity Risk Classification Model Identifies Men at Increased Risk of All-Cause Mortality
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Health organizations recommend that body mass index (BMI) and waist circumference (WC) be measured together to estimate a person’s obesity-related health risk. When BMI and WC are high, a person’s risk of death and disease increases. Cardiorespiratory fitness (CRF) is a measure of a person’s ability to perform aerobic exercise. Despite the fact that CRF reduces health risk, even in people with high BMI or WC, measurement of CRF is not currently recommended alongside BMI and WC in healthcare settings. We sought to determine whether CRF will improve our ability to predict risk of death when both BMI and WC are already considered. We analyzed data from 31 267 adult male participants of the Aerobics Center Longitudinal Study (ACLS), a prospective study established in 1970 to examine associations between lifestyle factors and health risk. Baseline characteristics were recorded during medical examinations taking place at the Cooper Clinic in Dallas, Texas between 1974 and 2002. Participant follow-up continued until either death or December 31st, 2003. Participants were first categorized by BMI according to whether they were normal BMI, overweight, or obese. They were then grouped according to whether their WC was high or normal based on their BMI category. CRF was assessed by a treadmill exercise test performed to voluntary exhaustion. Participants with the lowest 20% times on treadmill were classified as unfit, while the remaining 80% were classified as fit. Our primary results are that, for most combinations of BMI and WC, unfit men were at significantly higher risk of mortality compared with fit men within the same BMI and WC group. Higher mortality risk due to low fitness was observed in males with normal BMI regardless of WC, in males who were overweight with normal WC, and in males who were obese with high WC. Our observations add support to the idea that CRF should be measured in healthcare settings along with BMI and WC to help identify and manage health risk associated with overweight and obesity.