# Adiposity and mortality among intensive care patients with COVID-19 and non-COVID-19 respiratory conditions: a cross-context comparison study in the UK

## TL;DR

This study finds that obesity is linked to higher death rates in COVID-19 ICU patients but lower death rates in non-COVID-19 respiratory patients, suggesting these associations may be influenced by biases.

## Contribution

The study compares the causal relationship between adiposity and mortality across temporal and geographical contexts in ICU patients with and without COVID-19.

## Key findings

- Higher BMI is associated with increased mortality in COVID-19 patients, especially those with extreme obesity.
- Higher BMI is associated with decreased mortality in non-COVID-19 respiratory patients.
- The observed associations vary over time and are likely influenced by confounding and selection biases.

## Abstract

Adiposity shows opposing associations with mortality within COVID-19 versus non-COVID-19 respiratory conditions. We assessed the likely causality of adiposity for mortality among intensive care patients with COVID-19 versus non-COVID-19 by examining the consistency of associations across temporal and geographical contexts where biases vary.

We used data from 297 intensive care units (ICUs) in England, Wales, and Northern Ireland (Intensive Care National Audit and Research Centre Case Mix Programme). We examined associations of body mass index (BMI) with 30-day mortality, overall and by date and region of ICU admission, among patients admitted with COVID-19 (N = 34,701; February 2020–August 2021) and non-COVID-19 respiratory conditions (N = 25,205; February 2018–August 2019).

Compared with non-COVID-19 patients, COVID-19 patients were younger, less often of a white ethnic group, and more often with extreme obesity. COVID-19 patients had fewer comorbidities but higher mortality. Socio-demographic and comorbidity factors and their associations with BMI and mortality varied more by date than region of ICU admission. Among COVID-19 patients, higher BMI was associated with excess mortality (hazard ratio (HR) per standard deviation (SD) = 1.05; 95% CI = 1.03–1.07). This was evident only for extreme obesity and only during February–April 2020 (HR = 1.52, 95% CI = 1.30–1.77 vs. recommended weight); this weakened thereafter. Among non-COVID-19 patients, higher BMI was associated with lower mortality (HR per SD = 0.83; 95% CI = 0.81–0.86), seen across all overweight/obesity groups and across dates and regions, albeit with a magnitude that varied over time.

Obesity is associated with higher mortality among COVID-19 patients, but lower mortality among non-COVID-19 respiratory patients. These associations appear vulnerable to confounding/selection bias in both patient groups, questioning the existence or stability of causal effects.

The online version contains supplementary material available at 10.1186/s12916-024-03598-3.