The Joint Association Of Cardiorespiratory Fitness And Body Mass Index On All-cause Mortality: A Meta-analysis

PURPOSE: Obesity is associated with all-cause mortality (ACM). However, previous studies have shown that improvements in cardiorespiratory fitness (CRF) attenuate the increased risk of ACM associated with obesity. The purpose of this meta-analysis was to assess the joint associations of CRF and body mass index (BMI; normal – 18.5-24.9 kg/m2, overweight – 25.0-29.9 kg/m2, and obese – >30 kg/m2) on ACM. METHODS: Electronic databases (PubMed/MEDLINE, Web of Science, and SportDiscus) were searched for articles published between January 1980 and February 2023, with a priori inclusion criteria: 1) prospective study design, 2) CRF assessed using a maximal or VO2peak exercise test, 4) BMI reported and directly measured in clinic, 5) joint impact of CRF and BMI on ACM was analyzed, 6) included a reference group of normal weight, fit individuals. Pooled hazard ratios (HR) and confidence intervals (CI) were estimated using a three-level, restricted maximum likelihood estimation random-effects model, with robust variance estimation. α was set at 0.05. RESULTS: A total of 16 studies met the inclusion criteria, with a mean age 42.4-64.4 years, and mean follow-up 7.7-17.6 years. When compared to the reference group, fit-overweight (HR [95%CI]: 0.96 [0.61-1.50]) and fit-obese (1.11 [0.88-1.40]) were not associated with increased risk of ACM. However, unfit-normal weight (1.92 [1.43-2.57]), unfit-overweight (1.82 [1.47-2.24]), and unfit-obese (2.04 [1.54-2.71]) groups were all associated with increased ACM in comparison to the reference group. CONCLUSION: CRF is a strong predictor of ACM across all BMI strata. Overweight and obesity are not associated with higher ACM in fit individuals.