Obesity is a major risk factor for adverse outcomes after COVID-19 infection. However, it is unknown if the worse outcomes are due to the confounding effect of demographic and obesity-related comorbidities. The study objective is to analyze associations between body mass index, patient characteristics, obesity-related comorbidity, and clinical outcomes in COVID-19 patients.

In this prospective cohort study, we chose patient records between March 1st, 2020, and December 1st, 2022, in a large tertiary care center in southeast Wisconsin in the United States. Patients over the age of 18 who tested positive were included in the study. Clinical outcomes included hospitalization, intensive care unit (ICU) admission, mechanical ventilation, and mortality rates. We examined the characteristics of patients who had positive clinical outcomes. We created unadjusted logistic regression models, sequentially adjusting for demographic and comorbidity variables, to assess the independent associations between BMI, patient characteristics, obesity-related comorbidities, and clinical outcomes.

From a record of 1.67 million inpatients and outpatients at Froedtert Health Center, 55,299 (BMI: 30.5 ± 7.4 kg/m², 62.5 % female) tested COVID-19 positive during the study period. 17,580 (31.8 %) patients were admitted to hospitals, and of hospitalized patients required ICU admission. 1038 (36.3 %) required mechanical ventilation, and 462 (44.5 %) died after a positive test for COVID-19. We found female patients show a higher hospitalization rate, while male patients have a higher rate of ICU admission, mechanical ventilation, and mortality. Obesity-related comorbidities are associated with worse outcomes compared to simple obesity without comorbidities. In logistic regression models, we found four similar V-shaped associations between BMI and four clinical outcomes. Patients with a BMI of 25 kg/m² are at the lowest risk for clinical outcomes. Patients with a BMI lower than 18 kg/m² or higher than 30 kg/m² are associated with a higher risk of hospitalization, ICU, mechanical ventilation, and death. After adjusting the model for demographic factors and hypertension and diabetes as two common comorbidities, we found that demographic factors do not significantly increase the risk. Obesity alone does not significantly increase the risk of severe clinical outcomes. Obesity-related comorbidities, on the other hand, resulted in a significantly higher risk of outcomes.

Obesity alone does not increase the risk of worse clinical outcomes after COVID-19 infection. It may suggest that the worse clinical outcomes of patients with obesity are mediated via hypertension and type 2 diabetes. Patients with obesity and comorbidities have a higher risk of poor outcomes. Obesity-related comorbidities, including hypertension and diabetes, are independently associated with poorer clinical outcomes among COVID-19 patients. At a BMI of more than 30 kg/m² or less than 18 kg/m², we found an increase in the risk of severe COVID-19 outcomes leading to hospitalization, ICU, mechanical ventilation, and death. The increased risk of severe outcomes is not attributed to patient characteristics but can be attributed to hypertension and diabetes.