COVID-19 hospitalization, death risk rise ‘sharply’ with BMI
Risks for severe COVID-19 complications start to rise among adults with a BMI of at least 23 kg/m², with effects greatest among those younger than 40 years, according to data published in The Lancet Diabetes & Endocrinology.
In an analysis of 6.9 million adults living in England, including data from more than 20,000 adults with COVID-19 who were hospitalized or died during the first wave, researchers also found that the risk for hospitalization was 5% higher for each unit increase in BMI and the risk for ICU admission was 10% higher for each unit increase.
“Obesity is clearly associated with severe COVID-19 outcomes — hospital admission, ICU admission and death, after a positive COVID-19 test,” Carmen Piernas-Sanchez, PhD, MSc, a research lecturer in the Nuffield department of primary care health sciences at the University of Oxford, U.K., told Healio. “Our large study also allowed us to look at specific groups. We found, for example, that obesity showed a stronger association with COVID-19 outcomes among younger adults, and as age went up, the association with BMI became weaker, to the point there was no association among people aged 80 years or older. That was surprising.”
Previous studies have reported that obesity is associated with more severe outcomes after COVID-19 infection, but this is the first to examine the consequences of excess weight on COVID-19 outcomes across the full range of BMI, according to the researchers.
In a prospective study, Piernas-Sanchez and colleagues analyzed electronic health records from 6,910,695 patients in the QResearch database in England between January and April 2020, all with at least one BMI measurement on record. The average BMI across the whole study group was 26.8 kg/m². Data were linked to Public Health England’s database of positive SARS-CoV-2 test results and death certificates from the Office for National Statistics. Outcomes were admission to the hospital, ICU admission and death due to COVID-19. Researchers used Cox proportional hazard models to estimate the risk for severe COVID-19.
Greater risk by age, race
Within the cohort, 13,503, or 0.2%, adults were admitted to the hospital, 1,601, or 0.02%, were admitted to an ICU, and 5,479, or 0.08%, died after a positive test for SARS-CoV-2.
The researchers observed J-shaped associations between BMI and hospital admission due to COVID-19, with an adjusted HR of 1.05 per kg/m² from the nadir at BMI of 23 kg/m² (95% CI, 1.05-1.05). The aHR for COVID-19 death was 1.04 (95% CI, 1.04-1.05).
Researchers also observed a linear association across the BMI range with ICU admission, with an aHR of 1.1 (95% CI, 1.09-1.1).
Data showed an interaction between BMI and age and ethnicity. Compared with adults aged at least 80 years, those aged 20 to 39 years had a 9% increased risk for hospital admission with COVID-19 (aHR per kg/m² = 1.09; 95% CI, 1.08-1.1) per each BMI unit increase above a BMI of 23 kg/m².
Similarly, Black adults had a 7% increased risk for COVID-19 hospitalization (95% CI, 1.06-1.08) vs. a 4% risk(95% CI, 1.04-1.05) for white adults per each BMI unit increase above a BMI of 23 kg/m².The risks for hospital and ICU admission due to COVID-19 were associated with a unit increase in BMI that was slightly lower among adults with type 2 diabetes, hypertension and cardiovascular disease compared with those without those comorbidities.
“Clinicians should use BMI in deciding on the risk for deterioration alongside comorbidities, for example, in deciding whether to treat at home or refer to hospital,” Paul Aveyard, PhD, FRCP, FRCGP, FFPH, professor of behavioral medicine in the Nuffield department of primary care health sciences at the University of Oxford, U.K., told Healio. “We need to understand how body fat and COVID-19 are interacting to cause severe disease. Given that excess weight seems to affect the way we react to COVID-19 infection, it seems important to assess how well the vaccines are working in people with obesity.”
The authors noted that the BMI findings may be limited by the smaller sample of people with recent BMI measurements. However, the findings did not change when the researchers excluded BMI measurements that were more than 1 year old at the start of the study period.
Piernas-Sanchez said the researchers are planning to conduct follow-up studies on cohorts from the second and third waves of COVID-19 in the U.K. to assess whether the association between rising BMI and severe disease outcomes remains.
Emerging BMI questions
In commentary accompanying the study, Krishnan Bhaskaran, PhD, professor of statistical epidemiology and a Wellcome senior research fellow of the London School of Hygiene & Tropical Medicine, U.K., wrote that key future research priorities will be to establish whether BMI affects vaccine efficacy, and to understand whether people outside the healthy BMI range are at increased risk for post-COVID-19 sequalae.
“Further careful epidemiological study of these and other emerging questions will inform the ongoing public health response to this new disease that is likely here to stay,” Bhaskaran wrote.
Bhaskaran K. Lancet Diabetes Endocrinol. 2021;doi:10.1016/s2213-8587(21)00109-1.