Available online 16 April 2024

Author links open overlay panel, , , , , , , , ABSTRACT1Introduction

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.

Section snippetsINTRODUCTION

It has been 3 years since the onset of the severe acute respiratory syn-drome-coronavirus-2 (SARS-CoV-2) pandemic, and various risk factors for severe illness and death due to coronavirus disease 2019 (COVID-19) have been identified. Obesity is a risk factor for the aggravation and mortality of COVID-19 [1], [2]. A systematic review and meta-analysis revealed that a higher body mass index (BMI) results in higher mortality among patients with COVID-19 [3]. Furthermore, a higher BMI increases the

Data source

We used administrative claims data from Japanese advanced treatment hospitals provided by the Medical Data Vision Co., Ltd. (Tokyo, Japan) (MDV). This database comprises data from over 460 affiliated hospitals (approximately 26% of the advanced medical hospitals in Japan). It includes basic patient characteristics (age, sex, weight, and height), diagnosis based on the International Classification of Diseases 10th Revision (ICD-10) codes, admission and discharge dates, survival status, and

Ethics statement

The Japanese Ethical Guidelines for Medical and Biological Research Involving Human Participants do not apply to clinical studies that solely utilize anonymized data [10]. As our research exclusively used anonymized data, it was exempted from the requirement of ethics approval.

Summary of the study population

Figure 1 shows a flowchart of the patient selection process. The study data included 154,731 patients with COVID-19 and 78,182 hospitalized patients with COVID-19 between January 2020 and December 2021. Of these, 58,944 patients met the eligibility criteria. Notably, most eligible patients were normal-weight patients, followed by overweight patients. Individuals with obesity class I or higher accounted for 10.1% of the population.

Figure 2 shows the BMI distribution for the entire population and

COVID-19 outcomes according to obesity classes

Table 2 presents a summary of COVID-19 outcomes according to obesity class. However, Figure 3 shows the comparison results among the BMI classes with statistical adjustments for observed potential confounders between BMI and COVID-19 outcomes. The risk of critical illness increased monotonically with the higher obesity class, with the highest risk observed in those with class III obesity and the lowest risk in underweight individuals. However, underweight individuals had a higher risk of

DISCUSSION

Our study identified two crucial findings among Japanese patients with COVID-19. First, we observed that as BMI increased, there was a higher risk of disease progression with COVID-19 severity. However, the risk of COVID-19 mortality was lowest at a BMI of approximately 25 kg/m2; lower and higher BMI values were associated with an increased risk for mortality. Second, our findings indicated that the association between BMI and progression for COVID-19 severity and mortality was more pronounced

CONCLUSIONS

In Japanese patients with COVID-19, a higher BMI was associated with the progression of COVID-19 severity, whereas lower and higher BMI were associated with mortality. These relationships were particularly evident in the younger populations.

FUNDING

This work was supported by the Research Program on Emerging and Reemerging Infectious Diseases from the Japan Agency Development, AMED [grant numbers JP21fk0108094, JP22fk0108133]; MHLW Research Program on Emerging and Reemerging Infectious Diseases [grant number JPMH21HA2011, JPMH23HA2011]; and departmental funding from the Department of Medical Statistics, Osaka Metropolitan University Graduate School of Medicine.

ROLE OF THE FUNDING SOURCE

The funders of the study had no role in study design, data collection, data analysis

INSTITUTIONAL REVIEW BOARD STATEMENT

Ethical review and approval were waived for this study due to the use of anonymized data.

INFORMED CONSENT STATEMENT

Patient consent was waived as this study only used anonymized data provided by MDV.

DATA AVAILABILITY STATEMENT

The data used in this study cannot be shared with external researchers according to the contract with MDV.

Declaration of Competing Interest

The authors declare no conflict of interest.

ACKNOWLEDGMENTS

I appreciate having received the 18th Award in the Category of Clinical Research Conferred by the Director of the West Japan Branch of the Japanese Society of Chemotherapy. We would like to thank Editage (www.editage.jp) for the English language editing.

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© 2024 Japanese Society of Chemotherapy, Japanese Association for Infectious Diseases, and Japanese Society for Infection Prevention and Control. Published by Elsevier Ltd. All rights reserved.