Since June, CDC has warned of a link between obesity and severe or fatal cases of Covid-19. But now, CDC in updated guidance is warning that all adults with excess weight—including those classified as overweight but not obese—are at an increased risk of Covid-19 complications.
How excess weight affects Covid-19 risk
Since the start of the novel coronavirus pandemic, providers around the world have suspected that having excess weight increases a person's risk of developing a severe case of Covid-19, the disease caused by the virus, and of dying from the disease. However, researchers for a while struggled to determine whether it was obesity or other health conditions that are linked to excess weight that caused such patients to develop severe cases of and die from Covid-19 at higher rates than people with what are considered healthy body mass indexes (BMIs).
Over time, several studies suggested that obesity, itself, appeared to cause some patients infected with the novel coronavirus to become severely ill. And based on that evidence, CDC in June began warning that U.S. adults who are considered obese—which is defined as having a BMI of 30 or higher—have a heightened risk of developing severe cases of and dying from Covid-19 when compared with adults with what's considered to be a healthy BMI (which ranges from 18.5 to 24.9).
Some researchers believe that the increased risk for obese patients may partially stem from how the coronavirus enters the body via an enzyme called the ACE2 receptor. This enzyme is located in cells that line the lungs and fat tissue, which means that patients with excess weight may be more likely to experience a high viral load.
In addition, obesity is linked to hyperinflammation and shortness of breath, two conditions that make it more difficult for someone to combat viral infection.
What the latest research says
But new evidence suggests that adults who are considered to be overweight (those with BMIs ranging from 25 to 29.9) also may be at increased risk of developing severe cases of or dying from Covid-19.
For example, a study published in the International Journal of Obesity in July found that overweight, hospitalized Covid-19 patients were more likely to require mechanical ventilation and were more likely to die than patients with healthy BMIs.
For the study, researchers evaluated the outcomes of more than 500 patients hospitalized in March and April at Downstate Health Sciences University in Brooklyn. Among those patients, 43% were obese, 30% were overweight, and 27% were of a healthy weight. After the researchers adjusted for age and other factors, such as whether the patients had diabetes, they found that the mortality rate was greater for overweight patients than patients with healthy BMIs and patients with obese BMIs. For instance, the researchers found that patients with overweight BMIs were 40% more likely to die than Covid-19 patients with healthy BMIs, while patients with obese BMIs were 30% more likely to die than patients with healthy BMIs.
Mohamed Rami Nakeshbandi, an assistant professor of infectious diseases at SUNY Downstate Health Science University who worked on the study, and Rohan Maini, a medical student who also worked on the study, said their findings clearly showed an increased risk of developing severe cases of Covid-19 and dying from the disease among patients with a BMI of at least 25.
In addition, a separate study published in Brain, Behavior, and Immunity in July—in which researchers examined the associations between lifestyle factors and Covid-19 severity among 760 men and women who had Covid-19 in the United Kingdom—showed similar results. Those researchers found that overweight people who were infected with the novel coronavirus were up to 39% more likely to be hospitalized than those of healthy weights.
Researchers have hypothesized that the increased risk among overweight people, as well as those with obesity, may be tied to adipose tissue, which is the fat tissue that's accumulated in the body and is biologically active. That tissue can cause metabolic abnormalities and changes, and it creates a chronic state of "low-grade inflammation in the body, even without an infection," the New York Times reports.
That inflammation could contribute to Covid-19 severity, researchers say. "Overweight is quite different than other diseases in terms of inflammation," Barry Popkin, a professor of nutrition at the University of North Carolina at Chapel Hill, said. "The fat tissue are inflamed for a long period of time, and it affects immune function more over time. It is a continuous insult."
For instance, Melinda Beck, a researcher who studies how nutrition affects immunity at the University of North Carolina at Chapel Hill, explained that adipose tissue can, over time, depress the immune system's ability to produce so-called "memory" cells that store information on pathogens the body has had contact with in the past, which can hinder the body's response to those and similar pathogens in the future. Beck said the effects are like those seen in elderly patients, whose immune systems tend to weaken as they age. She noted that, in some patients with excess weight, the immune cells of 30-year-olds "look like those of an 80-year-old."
Further, researchers and medical professionals have noted that excess abdominal weight can compress a person's chest cavity, diaphragm, and lungs, which could restrict breathing and make it harder for patients to combat pneumonia and other respiratory infections, according to the New York Times.
75% of US adults may be at higher Covid-19 risk because of excess weight
Based on the latest evidence, CDC last week updated its guidance to warn American adults who are overweight—and not just those who are obese—that they may be at an increased risk of developing severe cases of Covid-19 and dying from the disease.
Although research showing the risks for overweight adults so far is less clear than research showing the risks among obese adults, CDC concluded that the current evidence was strong enough to add being overweight to its list of medical conditions that "might" put people at "increased risk for severe" cases of Covid-19, according to the Los Angeles Times.
The new warning is especially notable because it means nearly 75% of U.S. adults are at risk of developing a severe case of or dying from Covid-19, the New York Times reports. The Times notes, "While about 40% of U.S. adults are obese, another 32% are simply overweight, among the highest rates of obesity and overweight in the world. By the new calculus, nearly three-quarters of Americans may be at increased risk of severe Covid-19 if infected with the coronavirus."
Popkin said CDC's new warning "greatly expands the risk to a pretty big chunk of the U.S. population."
Brook Belay, a medical officer at CDC, said, "It's important to make sure the public and individuals are aware of this potential risk." She added, "The message is to strive to make healthy changes on a daily basis, through healthy food choices, choices about physical activity, and getting sufficient sleep" (Rabin, New York Times, 10/10; Kaplan, Los Angeles Times, 10/9; Wu, New York Times, 9/29).