Over the past year, many scientific teams around the world have reported that obese people who contract the coronavirus are particularly likely to get dangerously ill.
A major new study of nearly 150,000 adults in more than 200 hospitals across the United States now paints a more detailed picture of the relationship between weight and Covid-19 results.
The study, conducted by a team of researchers as Centers for Disease Control and Prevention, confirmed that obesity significantly increases the risk of hospitalization and death in those who contract the virus. And in overweight people, the risk increases with the patient’s body mass index or BMI, a ratio of weight to height. Patients with a BMI of 45 or higher, which is severely obese, were 33 percent more likely to be hospitalized and 61 percent more likely to die than patients of healthy weight.
“The results of the study underscore the serious clinical public health implications of elevated BMI and suggest the continued need for intensive treatment for Covid-19 disease, particularly in patients with severe obesity,” said lead author Lyudmyla Kompaniyets, a Health economist with the Department of Nutrition, Physical Activity, and Obesity at the CDC
However, the relationship between weight and results is nuanced. Underweight Covid-19 patients were also hospitalized more often than healthy-weight patients, although they were not admitted to the intensive care unit or died more often.
Dr. Kompaniyets and her colleagues used a database of Covid-19 cases to identify 148,494 adults who were diagnosed with the disease in American hospitals from March to December. They calculated each patient’s BMI and looked for correlations between the BMI and a number of serious outcomes, including hospitalization, ICU admission, mechanical ventilation, and death.
They found that obesity, defined as a BMI of 30 or higher, increased the risk of both hospitalization and death. Patients with a BMI of 30 to 34.9 were only 7 percent more likely to be hospitalized and 8 percent more likely to die than people of healthy weight. However, the risks increased sharply with increasing BMI.
The provision of evidence for this type of “dose-response relationship” makes the study particularly compelling, said Dr. Anne Dixon, director of pulmonary and critical care medicine at the University of Vermont Medical Center, who was not involved in the research. “What it shows is the more severe your obesity, the worse the effect. And the fact that it gradually increases with obesity, in my opinion, adds some kind of biological plausibility to the relationship between obesity and the outcome. “
The association between obesity and poor outcomes was strongest in those under 65, but it was also true in older adults. Previous smaller studies did not find strong associations between obesity and Covid-19 severity in older adults.
“Potentially because they had more strength from this large sample, they showed that obesity remains a major risk factor for death even in older adults,” said Dr. Michaela R. Anderson, an expert in pulmonary and critical care medicine at Columbia University Medical Center, who was not involved in the study. “It’s a beautifully done study with a huge population.”
March 8, 2021, 7:09 p.m. ET
Dr. Kompaniyets and her colleagues also documented a linear relationship between BMI and the likelihood of requiring mechanical ventilation. The higher the BMI, the more likely it was that a patient would need such an intervention, which is invasive and can have serious complications.
The study also found that those who were underweight and had a BMI below 18.5 were 20 percent more likely to be hospitalized than those of a healthy weight. The reasons are not entirely clear, but may be due to the fact that some of these patients were malnourished, frail, or had other illnesses.
The BMI range associated with the best results, according to the researchers, was close to the dividing line between healthy and overweight, which is in line with some previous research suggesting that a few extra pounds could help keep people safe, if they contract an infectious disease.
“It is not currently known exactly why this association exists,” said Dr. Alyson Goodman, pediatrician and medical epidemiologist at the CDC and co-author of the study. One possibility is that a little extra fat can provide much-needed energy reserves over the course of a long illness.
The results show the importance of carefully managing the care of patients with severe obesity and ensuring that people with obesity have access to vaccines and other preventive measures.
“This is just further evidence of the recommendation to vaccinate people with a high BMI as early as possible,” said Sara Y. Tartof, an infectious disease epidemiologist at Kaiser Permanente’s Department of Research & Evaluation, who was not involved in the study .