Study population and setting
This study assessing obesity as a risk factor for COVID-19 mortality included 6,916 members (55% female, mean age 49 years) of Kaiser Permanente Southern California (KPSC) who were diagnosed with COVID-19 from February 13 to May 2, 2020. Cases could be diagnosed clinically or via laboratory-confirmed SARS-CoV-2 infection. Pregnant women were excluded because of non-comparable BMI. The authors used Poisson models, including age- and sex-stratified versions, adjusted for possible confounding variables to estimate the association between BMI and mortality. BMI was categorized as underweight (<18.5 kg/m2), normal (18.5-24 kg/m2), overweight (25-29 kg/m2), obese class I (30-34 kg/m2), obese class II (35-39 kg/m2), obese class III (40 or greater kg/m2), and those with 45 or greater kg/m2. The outcome was death within 21 days of a COVID-19 diagnosis. Potential confounding covariates were considered at both the individual and neighborhood levels; calendar time was also considered to account for any changes in testing, social distancing, and clinical treatments over the study period. Authors selected covariates based on bivariate associations with mortality; no neighborhood-level covariates were included in final models.
Summary of Main Findings
The mean BMI was 30.6 kg/m2. Fifty-four percent of patients were Hispanic, 78% of patients lived in census tracts with median annual household incomes below $80,000, and 8% received Medicaid. The most common comorbidities were hypertension (24%), high cholesterol (23%), and diabetes (20%). Of the 206 (3%) patients who died within 21 days of diagnosis, 67% were hospitalized and 43% were intubated prior to death. Of survivors, 15% were hospitalized and 3% were intubated. In the primary adjusted model, there was a J-shaped relationship between BMI categories and the risk of mortality. Obese class III (relative risk [RR]: 2.68, 95% CI 1.43-3.02) and BMI ≥ 45 (RR: 4.18, 2.12-8.26) were associated with higher risks of mortality relative to normal weight. These associations, particularly those in the highest BMI categories, were larger in magnitude than those observed for most comorbidities. In separate sex-stratified and age-stratified analyses, associations between BMI categories and mortality were restricted to men, and to those 60 and younger. Race and ethnicity were not associated with mortality in adjusted models.
The study drew from a very large cohort of patients in one health care system, including both hospitalized and non-hospitalized COVID-19 cases, which allowed the authors to consider a wide range of clinical, demographic, and treatment covariates that were measured with a high degree of standardization.
Covariates were chosen for the adjusted models by virtue of their associations with mortality; many of these covariates (such as myocardial infarction and hypertension) are plausibly on the causal pathway between BMI and mortality. Adjusting for these covariates could introduce bias in effect estimates. This possibility is enhanced by the large number of comorbidities included in the models. Similarly, effect estimates for race and ethnicity should not be interpreted as net causal effects, as models were not constructed with the aim of estimating these. Additionally, patients with more severe disease tended to have more complete data.
This study provides further evidence that obesity is a risk factor for severe COVID-19.
This review was posted on: 24 August 2020