Effects of mild obesity on outcomes in Japanese patients with COVID-19: a nationwide consortium to investigate COVID-19 host genetics

Background: Obesity is reported to be a risk factor for severe disease in patients with coronavirus disease 2019 (COVID-19). However, there are no specific reports on the risk of severe disease according to body mass index (BMI) in Japan. Thus, this study aimed to investigate the effect of obesity stratified by BMI on the severity of COVID-19 in the general Japanese population. Methods: From February 2020 to May 2021, 1 837 patients aged ≥18 years were enrolled in the Japan COVID-19 Task Force. Patients with known BMI and disease severity were analyzed. Severity was defined as critical if the patient was treated in the intensive care unit, required invasive mechanical ventilation, or died. Results: Class 1 obesity (25.0 ≤ BMI < 30.0 kg/m²), class 2 obesity (30.0 ≤ BMI < 35.0 kg/m²), and class 3 or 4 obesity (BMI ≥ 35 kg/m²) were present in 29%, 8%, and 3% of the cases, respectively. Multiple logistic regression analysis with known risk factors for critical illness indicated that class 2 obesity was an independent risk factor for oxygenation (adjusted odds ratio, 4.75) and critical cases (adjusted odds ratio, 1.81). Class 1 obesity and class 3 or 4 obesity were independent risk factors for oxygen administration (adjusted odds ratios 2.01 and 3.12, respectively), but not for critical cases. However, no differences in the mortality rates were observed between the BMI classes (P = 0.5104). Conclusion: Obesity is a risk factor for respiratory failure in Japanese patients with COVID-19, regardless of the degree of obesity. However, it may not cause severe COVID-19 in a dose–response relationship with BMI. COVID-19 patients with mild obesity may benefit from aggressive intensive care.