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March 10, 2021

What's the link between obesity and severe Covid-19? Here's what a new CDC study says.

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    Obesity is correlated with a substantial increase in the risk of hospitalization, the need for a ventilator, and fatality risk among those who have contracted Covid-19, according to a recent study of nearly 150,000 adults in CDC's Morbidity and Mortality Weekly Report.

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    Obesity poses an increased risk for severe Covid-19

    For the study, researchers looked at data on 148,494 adults who received a Covid-19 diagnosis during either an ED or inpatient visit at 238 hospitals in the United States between March and December 2020. The researchers then calculated the body mass index (BMI) of each patient and identified correlations between BMI and several adverse health outcomes, including the need for hospitalization, ICU admission, the need for mechanical ventilation, and death.

    Overall, 71,491 of the adults included in the study were hospitalized. Of the hospitalized patients, nearly 50% were admitted to the ICU, 13.3% required ventilation, and 11.7% passed away, CDC found. In this hospitalized population, 50.2% had obesity, which was defined as a BMI of at least 30, and 27.8% qualified as overweight, which was defined as having a BMI of 25 or more.

    The researchers found that obesity correlated with an increased risk of hospitalization and death, and that the risk of severe Covid-19 "sharply increased" as BMIs rose. And that was true not only in younger adults—where the correlation was strongest—but also among those ages 65 and older, where earlier, smaller populations hadn't yet established a strong link between obesity and Covid-19 severity.

    For example, the study found that those who had obesity were 7% more likely to require hospitalization and 8% more likely to die from Covid-19 than those at a healthy weight.

    In comparison, patients who had severe obesity, which was defined as having a BMI of at least 45, were 33% more likely to be hospitalized with Covid-19 and 61% more likely to die than those who were at a healthy weight. Those with severe obesity were also twice as likely to require ventilation as those at a healthy weight.

    The researchers also found that patients who were underweight, which was defined as having a BMI below 18.5, were 20% more likely to be hospitalized with Covid-19 than those at a healthy weight.

    Those whose BMIs were within the healthy range but near the line of being considered overweight had the best Covid-19 outcomes, the researchers found.

    Ultimately, CDC said the findings demonstrate the "clinical and public health implications" of higher BMIs, as well as the need for "policies to ensure community access to nutrition and physical activities that promote and support a healthy BMI." The agency added that healthy BMIs may be particularly important for Hispanic, Latino, and Black populations, as well as people in lower-income households, all of whom are more likely to experience worse health outcomes from Covid-19 than other populations.

    CDC cited several limitations to the study, including that risk estimates were calculated only among adults who sought care at a hospital, which means the estimates may differ when considering all adults with Covid-19, and that the study included only patients for whom weight and height information was provided.


    Several experts praised the quality of CDC's study and the size of its population.

    Anne Dixon, director of pulmonary and critical care medicine at the University of Vermont Medical Center, who was not involved in the study, said the research was compelling because it showed a "dose response" relationship between obesity and severe Covid-19.

    "What it shows is the more severe your obesity, the worse the effect is," she said. "And the fact that [it] goes up stepwise with increasing levels of obesity ... adds sort of biological plausibility to the relationship between obesity and the outcome."

    Sara Tartof, an infectious disease epidemiologist at the Department of Research & Evaluation at Kaiser Permanente, who was not involved in the study, said the study "provides further evidence for the recommendation to vaccinate those with a high BMI as early as feasible."

    According to a report from the Kaiser Family Foundation, just 15 states have expanded vaccine eligibility to those who are considered obese or morbidly obese. Overall, about 42% of the United States' population was considered obese as of 2018, according to CDC's latest statistics (Anthes, New York Times, 3/8; Owens, "Vitals," Axios, 3/9; Lovelace Jr., CNBC, 3/8; Weixel, The Hill, 3/8; Kompaniyets et. al., Morbidity and Mortality Weekly Report, 3/8).

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