From the start of the pandemic, the coronavirus seemed to target people carrying extra kilos. Patients who were overweight or obese were more likely to develop severe COVID-19 and more likely to die.
Although these patients often have health conditions such as diabetes that compound their risk, scientists have become increasingly convinced that their vulnerability has something to do with obesity itself.
Now researchers have found that the coronavirus infects both fat cells and certain immune cells within body fat, prompting a damaging defensive response in the body.
“The bottom line is, ‘Oh, my God, indeed, the virus can infect fat cells directly,’” said Philipp Scherer, a scientist who studies fat cells at UT Southwestern Medical Centre in Dallas, who was not involved in the research.
“Whatever happens in fat doesn’t stay in fat,” he added. “It affects the neighbouring tissues as well.” …
Body fat used to be thought of as inert, a form of storage. But scientists now know that the tissue is biologically active, producing hormones and immune system proteins that act on other cells, promoting a state of nagging low-grade inflammation even when there is no infection.
Inflammation is the body’s response to an invader and sometimes it can be so vigorous that it is more harmful than the infection that triggered it. …
“Maybe that’s the Achilles’ heel that the virus utilises to evade our protective immune responses — by hiding in this place,” said Dr Vishwa Deep Dixit, a professor of comparative medicine and immunology at Yale School of Medicine. …
A man whose ideal weight is 77 kilograms but who weighs 113 kilos is carrying a substantial amount of fat in which the virus may “hang out”, replicate and trigger a destructive immune system response, said Dr David Kass, a professor of cardiology at Johns Hopkins.
“If you really are very obese, fat is the biggest single organ in your body,” Kass said.
The coronavirus “can infect that tissue and actually reside there,” he said. “Whether it hurts it, kills it or at best, it’s a place to amplify itself — it doesn’t matter. It becomes kind of a reservoir.”
As the inflammatory response snowballs, cytokines trigger even more inflammation and the release of additional cytokines. “It’s like a perfect storm,” Kass said.
Pre-vaccine, 73% of those who died of (or with) Covid-19 [in the US] were either overweight or obese — which tracks with the percentage of overweight and obese Americans. …
A September 2020 meta-analysis suggested a linear relationship between BMI and Covid-19 severity and mortality.