Objectively assessed cardiorespiratory fitness and all-cause mortality risk: an updated meta-analysis of 37 cohort studies involving 2,258,029 million

Though the evidence points to an inverse and independent association between cardiorespiratory fitness (CRF) and all-cause mortality risk, there exist inconsistencies regarding the strength and specificity of the association. Numerous studies evaluating the association between CRF and mortality have been published since the last relevant meta-analysis on this topic in 2009. Thus, we aimed to evaluate in more detail the magnitude and specificity of the association between CRF and all-cause mortality risk in an updated meta-analysis. Observational cohort studies with at least one year of follow-up were sought from inception until December 2021 in MEDLINE, Embase, Web of Science and manual search of relevant articles. Relative risks (RRs) with 95% confidence intervals (CIs) were pooled using random-effects models. Quality of the evidence was assessed using the GRADE tool. A total of 37 unique studies comprising of 2,258,029 participants with 108,613 all-cause mortality events were eligible. The pooled multivariable-adjusted RR (95% CI) for all-cause mortality comparing the top vs bottom tertiles of CRF levels was 0.55 (0.50-0.61). When CRF was expressed in metabolic equivalents (METs), the corresponding pooled RR (95% CI) was 0.56 (0.50-0.62). For every 1-MET increase in CRF, the RR (95% CI) for all-cause mortality was 0.89 (0.86-0.92). Strength of the association did not differ by publication year, age, sex, follow-up duration, CRF assessment method, and risk of bias. GRADE quality of the evidence was very low. Aggregate analysis of observational cohort studies confirms a strong inverse and independent association between CRF and all-cause mortality risk. The pooled updated results suggest that guideline bodies should consider the inclusion of CRF in standard risk panels for mortality risk assessment.