COVID-19 attacks fat tissue, may increase risk of severe disease, study finds

Obesity has become a risk factor for infection, severe disease, and death — and now, a new study is examining obesity and its connection to COVID-19. 

The study — published in the online medical journal bioRxiv on Oct. 25, explains how adipocytes, a fat cell, and adipose tissue, commonly known as body fat, are tolerated by the SARS-CoV-2 infection and how the virus can trigger a deleterious inflammatory response in the body. 

These inflammatory triggers can be especially harmful to those who are overweight or are considered higher risk for severe illness, hospitalization and death if they fall ill with COVID-19. 

Co-authors of the study and professors at Stanford University, Dr. Catherine A. Blisch and Tracey McLaughlin indicated their research reveals the impact COVID-19 can have specifically on fat tissue and how it impacts the rest of the body’s crucial organs. 

RELATED: Nearly two-thirds of COVID-19 hospitalizations attributed to 4 common underlying conditions, NIH says

"This study shows that SARS-CoV-2, the virus that causes COVID-19, actually can infect cells within human adipose tissue which is human fat. We looked at this because there have been quite a bit of evidence linking obesity to severe COVID-19 disease," McLaughlin said. 

"In the past, it’s been shown that some viruses actually can infect various cells in fats, and we wanted to see if it could infect the cells in human fats and that might provide a reservoir for viral replication or cause inflammation in the fat because fat is known to get inflamed. Obesity is considered a state of chronic low-grade inflammation which is coming from the fat so those were the things we investigated in the study," McLaughlin added.

Blisch said not only does COVID-19 negatively impact fat tissue, but their findings showed that once the virus is stored in the body’s fat it can contribute to severe inflammation. 

"We not only found evidence that we could show in a tissue culture dish that fat tissue could be infected by the virus and that that drove inflammation. But we also found evidence in a number of patients who had, unfortunately, died from COVID that we could detect evidence of the virus in their fat tissue indicating that this likely does happen in the setting of at least more severe infections," Blisch says.

The study also included analysis of fat tissue from various autopsies, which revealed the possibility that obese people with more fat can have a higher chance of harboring more material of the virus.

"When a cell gets infected, we typically see a lot of different things that can happen. The first is do we see evidence of the virus reproducing itself and we saw evidence that it was happening. Importantly the cell itself will induce genes trying to fight and stop that virus from replicating. And we saw some of those genes be produced. But we also saw some of those genes are inflammatory genes that communicate with other cells and try to prepare those cells and help protect them from future infection," explained Blisch. 

Still, McLaughlin said more research is needed to determine the exact cause of a harmful inflammatory response. 

"Obese individuals could be at higher risk because they have more fat, and they can harbor more virus, or it could be because their fats tend to have a greater inflammatory response when infected. We really don’t know if it does because we haven’t directly compared need to obese," McLaughlin said. 

The difficulty in determining how COVID-19 impacts fat tissue, specifically in those who are obese comes down to the fact that obesity is a complex issue. 

"There are certain different types of obesity. Some people have what’s called metabolic syndrome and they’re more prone to inflammation and hypercoagulation and all those things than other people who are also obese but don’t have that, so those are things that remain to be investigated. Some people tend to have a lot of fat around their organs, internal fat, some people call it visceral fat. It might be that if they have a lot of that kind of fat, you might be vulnerable to the bad consequences of inflammation," McLaughlin said.

According to the Centers for Disease Control and Prevention, people who are overweight face a greater risk of severe illness from COVID-19. There were over 900,000 COVID hospitalizations in the United States between the start of the pandemic and Nov. 18, 2020. Of those, hospitalizations, approximately 271,800 were connected to obesity. 

The CDC conducted a study of COVID-19 patients 18 years or younger and found that having obesity increased the chances of being hospitalized and a risk of severe illness.

Blisch and McLaughlin’s study follows countless studies which prove how harmful COVID-19 can be for those who are obese. 

Earlier this year, the CDC released a report that detailed a relationship between body mass index and COVID-19 severity. 

Researchers say individuals with the lowest risk for hospitalization and death are those with BMI’s near the threshold between healthy weight and overweight in most instances.

"Overweight and obesity were risk factors for invasive mechanical ventilation. Obesity was a risk factor for hospitalization and death, particularly among adults aged <65 years," the CDC said.

The CDC recognizes obesity as an underlying condition for severe illness caused by COVID-19. Additionally, obese and overweight individuals are at a higher risk of developing chronic inflammation that disrupts critical immune responses, the health agency stated.

Obesity is a common disease impacting human metabolism. The CDC estimates that more than 42% of U.S. adults suffer from it. 

The CDC has also found that nearly two-thirds of COVID-19 hospitalizations in the U.S. could be attributed to obesity, diabetes, hypertension, and heart failure, according to the National Institutes of Health.

A separate report by the NIH illustrates how common underlying medical conditions put people at higher risk for severe illness from the novel coronavirus.

The report cited a statistical model developed by researchers at Tufts University in Massachusetts led by Meghan O’Hearn and Dr. Dariush Mozaffarian.

Researchers found that more than 900,000 COVID-19 hospitalizations occurred through November 2020, 30% of which were attributed to patients with obesity. More than a quarter — 26% of patients — had hypertension, 21% had diabetes, and 12% had heart failure.

Currently, the CDC says that adults at any age with the following conditions are at increased risk of severe illness from the virus that causes COVID-19:

According to the CDC, it is estimated that 60% of all American adults have at least one chronic medical condition, so the latest changes to the agency’s list increase the number of people who fall into higher-risk groups.