A higher body mass index (BMI) was associated with increased risks for hospitalization and death due to COVID-19 and other respiratory infections as well, according to a study using data from the U.K. Biobank.

After a mean follow-up of 11.8 years, the hazard ratios per 10-unit higher BMI was 2.26 (95% CI 2.05-2.49) for severe COVID-19, 1.74 (95% CI 1.68-1.80) for severe lower respiratory tract infections (LRTIs), and 1.37 (95% CI 1.24-1.51) for severe upper respiratory tract infections (URTIs) in a fully adjusted model that accounted for age, sex, race, and a number of other factors (P<0.001 for trend for each).

“This study supports previous findings that 10-unit higher BMI is associated with about double the risk of severe COVID-19,” wrote Bastian Bohrmann, MSc, of the University of Oxford in England, and colleagues in JAMA. “In contrast, the limited previous evidence on the association of BMI with risk of severe LRTIs or URTIs shows substantial variation in the strength of these associations.”

With all three types of infections, the greatest risk for severe illness was seen among those with a BMI of 35-60:

• COVID: HR 2.38 (95% CI 2.07-2.74)
• LRTIs: HR 1.91 (95% CI 1.83-2.00)
• URTIs: HR 1.40 (95% CI 1.20-1.64)

“Several studies have described lower risk for LRTIs with higher BMI, but the current study found no such evidence in the BMI categories examined,” they added. “The findings suggest that the proposed mechanisms (including obesity-related chronic disease or compromised respiratory function) between BMI and COVID-19 might be shared by other LRTIs.”

The authors cited recent research addressing the link between BMI and severe COVID-19, as well as other illnesses such as influenza. A 2018 study also showed that obesity was associated with more frequent upper and lower respiratory tract infections when compared with “normal weight.”

In addition to being a risk factor for these infections, obesity is also associated with respiratory symptoms, such as orthopnea, dyspnea, and wheezing.

“The findings support individual and population-level approaches to reduce obesity and targeted vaccination programs for respiratory infections for individuals with a high BMI,” Bohrmann and colleagues concluded.

For this study, the authors used data from the prospective U.K. Biobank cohort. They excluded participants with prevalent chronic respiratory diseases, previous hospitalization for infectious respiratory diseases, and missing or extreme values for key variables.

A total of 476,176 participants were included. Median age was 58, 54% were women, and 94% were white. Mean BMI was 27.4.

Hazard ratios were adjusted for age at risk, sex, region, race, Townsend deprivation score, education, smoking, and alcohol intake.

Of the 20,302 participants who were hospitalized or died, 1,296 had COVID (144 died without prior hospitalization), 17,085 had an LRTI (273 died without prior hospitalization), and 1,504 had an URTI (none died without prior hospitalization).

Crude incidence rates for severe COVID ranged from 1.2 per 1,000 person-years for people with a BMI of less than 25 up to 5.8 per 1,000 person-years for those with a BMI of 35-60. For severe LRTIs, incidence rates ranged from 25.6 to 55.50 per 1,000 person-years across the BMI groups. Rates for severe URTIs ranged from 2.2 per 1,000 person-years for people with a BMI of less than 25 up to 4.4 per 1,000 person-years for those with a BMI of 35-60.

Bohrmann and team noted that associations could not be analyzed by subtypes of LRTIs, which was a limitation to their study. In addition, the U.K. Biobank is not representative of the general population, and “underweight” and “healthy-weight” groups could not be separated.

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