RESUMO
INTRODUCTION: Obesity is a risk factor for aggravation of and mortality from coronavirus disease 2019 (COVID-19). We aimed to investigate the relationship between COVID-19 and Body Mass Index (BMI) in the Japanese population. METHODS: We used administrative claims data from an advanced treatment hospital in Japan and extracted data from patients hospitalized for COVID-19. The exposure variable was BMI measured at the time of admission, and the study outcomes were progression to critical illness and death. Analyses were performed for each age group. RESULTS: Overall, 58,944 patients met the inclusion criteria. The risk of critical illness increased monotonically with higher BMI. In contrast, the relationship between BMI and mortality follows a J-shaped curve; being underweight and obese are risk factors for mortality. When stratified by age, similar trends were observed for both critical illness and mortality. CONCLUSION: A higher BMI is a risk factor for the progression of COVID-19 severity, whereas both lower and higher BMIs are risk factors for mortality in the Japanese population.