Adiposity and Mortality among Patients Severely Ill with COVID-19 and non-COVID-19 Respiratory Conditions: A Cross-Context Comparison Study in the UK

ObjectiveTo assess the causality of adiposity for mortality among patients severely ill with COVID-19 and non-COVID-19 respiratory conditions by examining the consistency of associations across temporal and geographical contexts where biases vary DesignProspective cohort study Setting297 intensive care units (ICUs) in England, Wales, and Northern Ireland monitored by the Intensive Care National Audit and Research Centre Case Mix Programme ParticipantsPatients aged [≥]16 years admitted to ICU with COVID-19 (N=33,352; Feb 2020-Aug 2021) and non-COVID-19 respiratory conditions (N=24,739; Feb 2018-Aug 2019) Main outcome measure30-day mortality post ICU admission ResultsCompared with non-COVID-19 respiratory patients, COVID-19 patients were younger, less often of a white ethnic group, and more often with extreme obesity (body mass index (BMI) [≥] 40kg/m2). COVID-19 patients had fewer comorbidities but higher mortality (35% vs. 23% mortality in non-COVID-19). Socio-demographic and comorbidity factors and their associations with BMI and mortality varied more by date than geographical region of ICU admission, particularly among COVID-19 patients. Among COVID-19 patients, higher BMI was associated with a small excess mortality (hazard ratio (HR) per standard deviation (SD)=1.05; 95% CI=1.03, 1.08), driven by extreme obesity (HR per SD=1.21; 95% CI=1.13, 1.31 vs. normal-weight). Extreme obesity was strongly associated with higher mortality only during Feb-April 2020 (HR=1.49, 95% CI=1.27, 1.73 vs. normal-weight); this association weakened thereafter (BMI-date interaction P=0.03). Among non-COVID-19 respiratory patients, higher BMI was associated with lower mortality (HR per SD=0.84; 95% CI=0.82, 0.87), seen across all overweight/obesity groups. These negative obesity-mortality associations were similar across most admission dates and regions. ConclusionsObesity is associated with higher mortality among COVID-19 patients, but lower mortality among non-COVID respiratory patients. These associations appear vulnerable to confounding/selection bias in both patient groups, questioning the existence or stability of causal effects. Among COVID-19 patients, unfavourable obesity-mortality associations differ by admission date. Among non-COVID-19 respiratory patients, favourable obesity-mortality associations may reflect comorbidity-induced weight loss.