The impact of cardiorespiratory fitness on COVID-19 related outcomes: the ETHOS Study

Abstract

Abstract Background Comorbidities such as cardiovascular disease, diabetes, obesity and hypertension are associated with more severe COVID-19 outcomes, but the relative impact of cardiorespiratory fitness (CRF) on outcomes in COVID-positive patients is largely unknown. Objective To assess the association between objectively measured CRF and COVID-19-related health outcomes including mortality, hospitalization, and mechanical ventilation in non-COVID vaccinated patients. Design, Setting and Participants. Retrospective analysis of 750,302 subjects (23,140 [mean age 65.8±12.0 years] with a positive COVID-19 test between March 2020 and September 2021) who underwent a maximal exercise test between 1999 and 2020. Main Outcomes and Measures. Association between all-cause mortality, hospitalization due to COVID-19, and need for intubation with risk for severe COVID-19 outcomes after adjustment for 15 covariates. Subjects were stratified into five age-specific CRF categories (Least-fit, Low-fit, Moderate-fit, Fit and High Fit), based on peak metabolic equivalents achieved. Results During a median of follow-up of 100 days, 1,643 (7.1%) patients died, 4,995 (21.6%) were hospitalized, and 927 (4.0%) required intubation for COVID-19 related reasons. When compared to the Least-Fit subjects (referent), the Low-Fit, Moderately-Fit, Fit, and High-Fit subjects had hazard ratios for mortality of 0.82 (95% CI; 0.72-0.93), 0.73 (95% CI; 0.63-0.86), 0.61 (95% CI; 0.53-0.72), and 0.54 (95% CI; 0.45-0.65), respectively (Figure). Subjects who were more fit also had significantly lower need for hospital admissions and intubation. Similar patterns were observed for elderly subjects and subgroups with comorbidities including hypertension, diabetes, cardiovascular disease, and chronic kidney disease; for each of these conditions, those in the High-Fit category had mortality rates that were roughly half those in the Low-Fit category. Conclusion Among subjects positive for COVID-19, higher CRF had a favorable impact on survival, need for hospitalization, and need for intubation regardless of age, BMI, or the presence of comorbidities.