People with obesity are already at heightened risk for a number of serious illnesses: diabetes, heart disease, some cancers. Severe COVID-19 can now be added to that list. Especially concerning is research that shows the risk is high among young adults, ages 20 to 39.
“I would daresay that almost all of the patients that we have seen who were young and did very poorly were all significantly obese,” says Aaron Eli Glatt, M.D., chief of infectious diseases and the hospital epidemiologist at Mount Sinai South Nassau in Oceanside, New York. “I can’t say it was 100%. But there were medically significant risk factors in terms of having bad COVID(-19) in the hospital in your 30s. And we see this literally almost every day of the pandemic.”
Glatt notes the difficulty of teasing out whether it is obesity itself that increases the risk of severe COVID-19 or the web of cardiovascular and metabolic disorders associated with being overweight or obese.
“I don’t know if we will ever have an absolute, definitive answer,” Glatt says. “But the overwhelming evidence certainly suggests that people who have obesity, whether that is the risk or not ... are far, far worse off if they have COVID-19. I don’t know how anybody can argue with that.”
The epidemiologic evidence of an association between obesity and severe COVID-19 and death is strong and not in dispute, at least during the early phase of the pandemic. A study published in March 2021 in the CDC’s Morbidity and Mortality Weekly Report that included more than 148,000 U.S. adults who received a COVID-19 diagnosis in 2020 showed that just over half (50.8%) of those who were hospitalized had obesity (a body mass index, or BMI, of 30 or more) and that just under half (46.0%) of those who died had obesity.
It is not entirely understood why obesity would worsen COVID-19, but researchers have proposed a number of explanations. Several theories trace the risk to the properties of adipose tissue in people with obesity. In a patient with obesity, the proinflammatory cytokines normally released by adipose tissue become amplified, and that amplification may lead to dysregulated immune function and greater difficulty fending off infections.
Leptin is one of those cytokines, and people with obesity can develop leptin resistance that is similar to insulin resistance that induces chronic inflammation. Adipose tissue in obesity is also a source of interleukin 6, a cytokine that may contribute to the runaway inflammation of the “cytokine storm” that characterizes many severe cases of COVID-19.
There’s also a theory that adipose tissue acts as a kind of reservoir for the SARS-CoV-2 virus and therefore plays a role in viral shedding. The extra adipose tissue in a person who is obese may mean a bigger SARS-CoV-2 reservoir and even more shedding.
Other explanations about the association between obesity and severe COVID-19 center on obesity’s effect on lung function. Central adiposity — the accumulation of adipose tissue in the abdomen — can limit expansion of the lungs. As a result, the lungs do not take in as much air, and that, in turn, means less oxygen reaches the blood.
“We are still learning about COVID-19 and its interaction with adipose tissue,” says Katherine H. Saunders, M.D., an obesity specialist and an assistant professor of clinical medicine at Weill Cornell Medicine in New York. “There will likely be several mechanisms identified that explain the greater prevalence of severe disease among people with obesity.”
Saunders mentions that the chronic inflammation associated with excess weight may make it harder for the immune system to protect the body against the SARS-CoV-2 virus and that individuals with obesity can have impaired lung function.
Obesity as a disease
One way to view obesity and COVID-19 is as two epidemics combining and accentuating one other.
Obesity is a risk factor for severe COVID-19, and the pandemic has led to weight gain.
A Harris Poll last year found that 42% of Americans said they had gotten heavier since the pandemic started in early 2020 and that the average weight gains was 29 pounds (the median was 15). Almost certainly that means many people in the U.S. went from being overweight to obese. With that change may have come a higher risk for developing diabetes, hypertension and, possibly, severe COVID-19.
Of course obesity has been a problem in the U.S. long before the pandemic. According to a February 2020 report from the National Center for Health Statistics (NCHS), the prevalence of obesity among adults in the U.S. increased from 30.5% in 1990-2000 to 42.4% in 2017-2018. During that same span, the prevalence of severe obesity increased from 4.7% to 9.2%. Health researchers define severe obesity as a BMI of 40 or higher. Some data suggest, though, that the rate at which the prevalence of obesity has been growing is slowing down some.
The figures in that NCHS report foreshadow to some extent that that COVID-19 might be bad news for 20- to 39-year-olds. The prevalence of the obesity in that age group was 40%, which was not that much lower than the prevalence of 44.8% among middle-aged adults, ages 40 to 59, and the prevalence of 42.8% among older people, ages 60 or more.
Obesity has been typically viewed through the lens of personal responsibility and individual choice. Attitudes are changing, but people with obesity are still viewed inaccurately as being lazy or undisciplined. For quite some time, public health officials and others have seen obesity differently. In 1948, the World Health Organization weighed in by classifying obesity as a disease. U.S. health officials were decades behind; 50 years later, the National Institutes of Health declared obesity a disease, followed in 2013 by the American Medical Association.
“Obesity is much more complex than most people realize,” says Saunders. “There are so many different pathways involved. We have learned so much in the last few decades,” says Saunders, the first physician to complete a fellowship in obesity medicine at the Comprehensive Weight Control Center at Weill Cornell Medicine. “There is exciting research happening right now. We have several very effective medications and there are even more in the pipeline.”
The obesity subspecialty is growing, with more than 5,200 board-certified obesity physicians, according to Saunders. Still, too many healthcare providers, not trained in obesity medicine, continue to rely on the traditional diet and exercise regimens. Diet and exercise are the cornerstones of every weight loss program, Saunders says. But by themselves, they don’t work for everyone.
“When people with obesity try to lose weight with dietary strategies and they are not successful … they can and should seek medical treatment, because this is more than a lifestyle problem for most people and medical treatment is warranted,” says Saunders, a co-founder of Intellihealth, a company that provides a medical approach to obesity. “The most important thing is that obesity is not a lifestyle problem. It’s not about willpower. It is a complex disease.”
Obesity is associated with more than many comorbidities. It’s one reason why, prior to the pandemic, it was, by some accounts, the second-leading cause of preventable deaths in America, killing between 280,000 and 300,000 Americans each year.
Meanwhile, the evidence for the danger of the COVID-19/obesity combination continues to pile up, although comorbidities are also involved. For example, a study published in the September 2021 issue of Clinical Microbiology and Infection looked at 134,209 French adults admitted to hospitals with COVID-19. The authors concluded that “mortality was more frequent among patients with obesity and diabetes.” They also noted that intubation was three times more frequent among patients with obesity than among patients without.
Three months later, a retrospective cohort study published in the journal Clinical Infectious Diseases echoed some of the French findings. The researchers combed through data on 66,000 patients with a COVID-19 diagnosis seen at 613 U.S. hospitals, 18.6% of whom died. Diabetes without chronic complications was not a risk factor for mortality, and hypertension without complications was only a risk factor in 20- to 39-year-olds. But diabetes with chronic complications, hypertension with chronic complications and obesity were risk factors at most ages and posed the greatest risk in the 20- to 39-year-old age group.
To avoid COVID-19 danger, Glatt tells patients — regardless of weight — to get vaccinated and boosted. But the recommendation is even stronger for people with obesity. “Obese people can have difficulty breathing because of the physical dynamics of their obesity,” says Glatt, referencing some of the current thinking about why severe COVID-19 is greater threat for people who are heavy. “They may not be in good shape and they don’t take deep breaths. Obesity can impair their immune function. There are so many complicating factors. It is extremely unusual that a patient is just obese and has no other medical problems.”
People with obesity may want to consider steps to lose the adiposity. “Begin to assess whether or not this is the weight you want to be at,” Glatt advises.
If one can think of a pandemic that is on its way to claiming a million American lives as having a silver lining, Saunders and her colleagues say that lining might be all the attention that obesity is getting as a bona fide health problem.
“Our mission is to make it clear to the medical community and beyond that obesity is something that is treatable and it is something that requires medical attention,” she says. “In terms of COVID-19, we do have evidence that treating obesity can reduce the risk of morbidity and mortality.”
Robert Calandra is an independent journalist in the Philadelphia area.