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How Obesity Exacerbates a Coronavirus Infection

Excess weight can complicate breathing and impact the body's immune response

Medical staff caring for a man in a hospital bed.

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En español | Physicians and researchers are noting a troubling trend among the more than 400,000 Americans who have been hospitalized with COVID-19 since the start of the pandemic: Many of them have obesity.

The disease, which has become increasingly prevalent in the last two decades and now affects around 42 percent of adults in the United States, is doing more than showing up as a common characteristic on patient charts. A number of studies have found that obesity, in and of itself, increases risk for hospitalization and intensive-care admissions among COVID-19 patients. (Obesity is defined as a body mass index, or BMI, of 30 or greater.)

It is also associated with a higher risk for death, especially in men and people under 60, according to research recently published in Annals of Internal Medicine. Even overweight adults (people who have a BMI between 25 and 30) may be at increased risk for severe illness from COVID-19, according to recent updates from the Centers for Disease Control and Prevention (CDC).


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"This is a unique confluence,” says David Kass, M.D., a cardiologist and professor of cardiology and medicine at Johns Hopkins Medicine. “We happen to have a pandemic of obesity, and we've never had a pandemic of obesity. And the last time we had a virus like this was in the early 20th century [with the Spanish flu].”

Experts are still studying the dangers that can arise when the two pandemics — obesity and COVID-19 — collide, but are gaining a better understanding of why obesity makes a coronavirus infection so dangerous.

Obesity, like COVID-19, can worsen breathing

Obesity is a risk factor for a number of underlying health conditions that are known to complicate a coronavirus infection, including diabetes, heart disease and high blood pressure. But it can also cause damage on its own.

For starters, people with obesity have a harder time breathing — and that's because excess weight, especially around the abdomen area, restricts the movement of the diaphragm, making it more difficult for the lungs to expand and fill with air, explains Fatima Cody Stanford, M.D., an obesity medicine physician at Massachusetts General Hospital in Boston.

"Literally, you can't move air in and out the same way; it actually reduces your lung capacity when you have excess weight,” Stanford says. “And that's just not a really good combination when we're looking at a respiratory illness like COVID,” which independently can cause shortness of breath, pneumonia and, in severe cases, a form of lung failure known as acute respiratory distress syndrome (ARDS).

What's more, doctors have found that positioning severely ill COVID-19 patients on their stomachs helps to better distribute oxygen and avoid ventilation. However, this method, called “proning,” is challenging in patients with obesity, again because the excess weight and pressure on the stomach hampers the movement of the diaphragm.

"This is all kind of tied up in what I'll call ‘the physics of breathing,’" Kass says. “And it's one of the reasons why with people who have severe obesity, it's going to be more difficult.”

Obesity affects the body's immune response

Obesity — and especially abdominal obesity, which is an accumulation of fat in the gut and around the internal organs — provokes chronic inflammation, a sort of lingering immune response that Kass likens to “an underlying immune brush fire.” When a virus, such as SARS-CoV-2, is introduced to the body, the immune system of a person who has this lurking inflammation “is not necessarily going to respond properly,” Kass says.


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On one hand, the immune system can overreact to a viral invasion, waging an all-out war on the body and causing more damage than the virus itself. (COVID-19 has also shown to provoke a hyperinflammatory immune response in some patients.) On the other hand, an immune system that is always “on” and slowly burning in the background can become somewhat exhausted, and its response to a new virus is delayed.

"It's a little bit like ‘the boy who cried wolf’ phenomenon,” Kass says. And with a delayed immune response, “the virus is going to have a much better shot at replicating before the immune system finally gets into action, but then you've got a lot more virus to deal with,” he adds.

Obesity puts some more at risk than others

There are a few other factors that scientists are studying when it comes to obesity's role in complicating a coronavirus infection. For example, SARS-CoV-2 attaches to a particular protein found on the cell surface that is expressed in the lungs and other organs we know COVID-19 affects. But it is also common in fat tissue, Kass says. This could make excess fat “like a big reservoir” for the virus, and may mean that people with excess weight harbor a higher viral load.

Stanford says it's also important to note that obesity rates in the U.S. are highest in Black and Hispanic Americans — two populations that have been disproportionately impacted by the coronavirus. Black Americans are over twice as likely to die from COVID-19, compared to their white peers, according to CDC data. And hospitalization rates are nearly five times higher for both Blacks and Hispanics, compared to whites.

Men with obesity may also have a harder time fighting COVID-19 than women. A study published in Annals of Internal Medicine found that a high BMI was associated with greater risk for death in male, but not female, patients. Kass says this could be because women tend to store less of the deleterious fat in their abdomens, compared with men.

The study's lead author, Sara Tartof, an infectious disease epidemiologist with the Kaiser Permanente Southern California Department of Research & Evaluation, says the findings point to the need for men and younger individuals with obesity to take preventive measures seriously.

"We should all be taking [preventive action], but these patients are a particularly high risk for death if they do contract COVID,” Tartof says. In the absence of a vaccine, the CDC says the best way to ward off COVID-19 is to avoid exposure to the virus: Limit your interactions with other people as much as possible, wash your hands often, practice social distancing and wear a face mask in public.

'Obesity is a disease'

If you do get a SARS-CoV-2 infection and have obesity, take it seriously. “Have a low bar” for following up on symptoms and treatment “because things could decline,” Tartof points out. “So be ready to seek health care earlier rather than later.”

Stanford says the biggest takeaway from the latest research on obesity and COVID-19 is to treat your obesity if you have it. If you've tried and have struggled to lose weight on your own, reach out to your doctor or an obesity specialist for help.

"Obesity is a disease; it's real,” Stanford adds. And while it seems to have a unique interplay with COVID-19, it also can complicate and worsen other infections and diseases.

"We're going to make it through COVID. But there's going to be another COVID,” Kass says. “And so in that sense, use this as a moment to think about how to make yourself healthier.”

This article, originally published on Sept. 11, 2020 was updated with new information on Oct. 12, 2020.

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