COVID-19 Severity Starts in Normal BMI Range, Especially in Young

Nancy A. Melville

May 05, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

The risk of severe outcomes with COVID-19 increases with excess weight in a linear manner beginning in normal body mass index ranges, with the effect apparently independent of obesity-related diseases such as diabetes and stronger among younger people and Black persons, new research shows.

"Even a small increase in body mass index above 23 kg/m² is a risk factor for adverse outcomes after infection with SARS-CoV-2," the authors reported.

"Excess weight is a modifiable risk factor and investment in the treatment of overweight and obesity, and long-term preventive strategies could help reduce the severity of COVID-19 disease," they wrote.

The findings shed important new light in the ongoing efforts to understand COVID-19 effects, Krishnan Bhaskaran, PhD, said in an interview.

"These results confirm and add detail to the established links between overweight and obesity and COVID-19, and also add new information on risks among people with low BMI levels," said Bhaskaran, an epidemiologist at the London School of Hygiene & Tropical Medicine, who authored an accompanying editorial.

Obesity has been well established as a major risk factor for poor outcomes among people with COVID-19; however, less is known about the risk of severe outcomes over the broader spectrum of excess weight, and its relationship with other factors.

For the prospective, community-based study, Carmen Piernas, PhD, of the University of Oxford (England) and colleagues evaluated data on nearly 7 million individuals registered in the UK QResearch database during Jan. 24–April 30, 2020.

Overall, patients had a mean BMI of 27 kg/m². Among them, 13,503 (.20%) were admitted to the hospital during the study period, 1,601 (.02%) were admitted to an ICU and 5,479 (.08%) died after testing positive for SARS-CoV-2.

Risk Rises From BMI of 23 kg/m²

In looking at the risk of hospital admission with COVID-19, the authors found a J-shaped relationship with BMI, with the risk increased with a BMI of 20 kg/m² or lower, as well as an increased risk beginning with a BMI of 23 kg/m² — considered normal weight — or higher (hazard ratio, 1.05).

The risk of death from COVID-19 was also J-shaped, however the association with increases in BMI started higher — at 28 kg/m² (adjusted HR, 1.04).

In terms of the risk of ICU admission with COVID-19, the curve was not J-shaped, with just a linear association of admission with increasing BMI beginning at 23 kg/m2 (adjusted HR, 1.10).

"It was surprising to see that the lowest risk of severe COVID-19 was found at a BMI of 23, and each extra BMI unit was associated with significantly higher risk, but we don't really know yet what the reason is for this," Piernas said in an interview.

The association between increasing BMI and risk of hospital admission for COVID-19 beginning at a BMI of 23 kg/m² was more significant among younger people aged 20-39 years than in those aged 80-100 years, with an adjusted HR for hospital admission per BMI unit above 23 kg/m² of 1.09 versus 1.01 (P < .0001).

In addition, the risk associated with BMI and hospital admission was stronger in people who were Black, compared with those who were white (1.07 vs 1.04), as was the risk of death due to COVID-19 (1.08 vs 1.04; P < .0001 for both).

"For the risk of death, Blacks have an 8% higher risk with each extra BMI unit, whereas whites have a 4% increase, which is half the risk," Piernas said.

Notably, the increased risks of hospital admission and ICU due to COVID-19 seen with increases in BMI were slightly lower among people with type 2 diabetes, hypertension, and cardiovascular disease compared with patients who did not have those comorbidities, suggesting the association with BMI is not explained by those risk factors.

Piernas speculated that the effect could reflect that people with diabetes or cardiovascular disease already have a preexisting condition which makes them more susceptible to SARS-CoV-2.

Hence, "the association with BMI in this group may not be as strong as the association found among those without those conditions, in which BMI explains a higher proportion of this increased risk, given the absence of these preexisting conditions."

Similarly, the effect of BMI on COVID-19 outcomes in younger patients may appear stronger because their rates of other comorbidities are much lower than in older patients.

"Among older people, preexisting conditions and perhaps a weaker immune system may explain their much higher rates of severe COVID outcomes," Piernas noted.

Furthermore, older patients may have frailty and high comorbidities that could explain their lower rates of ICU admission with COVID-19, Bhaskaran added in further comments.

The findings overall underscore that excess weight can represent a risk in COVID-19 outcomes that is, importantly, modifiable, and "suggest that supporting people to reach and maintain a healthy weight is likely to help people reduce their risk of experiencing severe outcomes from this disease, now or in any future waves," he concluded.

Piernas and Bhaskaran had no disclosures to report. Coauthors' disclosures are detailed in the published study.

Lancet Diabetes Endocrinol. Published online April 28, 2021. Full text, Editorial

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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