It may help explain why people who are overweight and obese are at higher risk of severe illness and death from Covid.
The coronavirus seemed to target people carrying extra weight from the beginning of the pandemic. Overweight and obese patients were more likely to develop severe Covid-19 and die from it.
The researchers have become increasingly convinced that these patients’ vulnerability has something to do with obesity itself, even though they often suffer from health conditions like diabetes that compound their risk.
Researchers have discovered that the Coronavirus infects fat cells and immune cells within body fat, resulting in a negative defensive response.
“The bottom line is, ‘Oh my god, the virus can infect fat cells directly,’” said Dr. Philipp Scherer, a scientist who studies fat cells at UT Southwestern Medical Center in Dallas.
“What happens in fat does not stay in fat,” he added. As well as the neighboring tissues, it affects them.”
Researchers at Weill Cornell Medicine in New York and elsewhere have already published earlier findings. Still, the new research has not yet been peer-reviewed or published in a scientific journal.
The findings may shed light not only on why overweight patients are vulnerable to the virus, but also on why certain young adults with no other risk become so ill.
A recent study by Dr. Tracey McLaughlin and Dr. Catherine Blish of Stanford University School of Medicine suggests new Covid treatments may target body fat.
“Maybe that’s the Achilles’ heel the virus uses to evade our protective immune responses,” said Dr. Vishwa Deep Dixit, a professor of comparative medicine and immunology at Yale School of Medicine.
This finding is especially relevant to the United States, which has one of the highest obesity rates in the world. 42 percent of American adults are overweight or obese. In the U.S., blacks, hispanics, Native Americans and Alaska Natives have higher obesity rates than whites and Asian Americans; they have also been disproportionately affected by the pandemic, with mortality rates roughly double whites.
The condition may well be contributing to severe disease, according to Dr. Blish. In response to infection of those tissues, we see the same inflammatory cytokines we see in the blood of really sick patients.”
As a form of storage, body fat was once considered inert. Despite this, scientists now know that the tissue is biologically active, producing hormones and immune system proteins that affect other cells, promoting low-grade inflammation even in the absence of infection.
A body’s response to an invader is inflammation, which can sometimes be more harmful than the infection that triggered it. According to Dr. McLaughlin, the more visceral fat around internal organs, the worse your inflammatory response.
Adipocytes, or fat cells, make up most of the fat tissue. Adipose tissue also contains preadipocytes, which mature into fat cells, as well as macrophages, a type of immune cell.
Dr. McLaughlin, Dr. Blish, and their colleagues examined how various types of cells responded to infection with the Coronavirus in fat tissue obtained from bariatric surgery patients.
Despite the fact that fat cells themselves could become infected, the scientists found that they did not become very inflamed. However, certain immune cells called macrophages can also become infected, leading to an inflammatory response.
Even stranger, the pre-adipocytes did not become infected, but contributed to the inflammatory response. (The scientists did not examine whether certain variants were more destructive than others in this regard.)
Researchers also obtained fat tissue from the bodies of European patients who had died of Coronavirus and found the virus in fat near various organs.
Dr. Dixit said the idea that adipose tissue serves as a reservoir for pathogens is not new. In addition to H.I.V., the influenza virus is known to be present in body fat.
Coronavirus appears to evade the body fat’s immune defenses, which are limited and incapable of combating it effectively. The amount of body fat can be high in obese individuals.
According to Dr. David Kass, a professor of cardiology at Johns Hopkins, a man who weighs 250 pounds is carrying a substantial amount of fat in which the virus can “hang out,” reproduce and trigger a destructive immune response.
According to Dr. Kass, fat is your body’s biggest organ if you are extremely obese.
“The Coronavirus can infect that tissue and reside there,” he said. It doesn’t matter whether it hurts it, kills it, or at best, it’s a place to amplify itself. As a result, it becomes a kind of reservoir.”
When the inflammatory response snowballs, cytokines trigger more inflammation and the release of additional cytokines. As he put it, “it’s like a perfect storm.”.
Blish and her colleagues speculated that infected body fat may even be responsible for “long Covid,” a condition characterized by fatigue after acute episodes that persists for weeks or months.
Additionally, Covid vaccines and treatments may need to take into account the weight and fat stores of patients.
This paper is another wake-up call for the medical profession and public health to examine more deeply the issues of overweight and obese individuals, and the treatments and vaccines we’re giving them,” said Barry Popkin, a professor of nutrition at the University of North Carolina at Chapel Hill, who has examined the increased risk that Covid poses to obese individuals.
“We keep documenting their risks, but we haven’t addressed them,” Dr. Popkin said.