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Researchers say a new study may help explain why the COVID-19 virus seems to hit particularly hard those who are obese, leading to a higher risk of severe illness and death.

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The study, which has not yet been peer-reviewed, showed that the virus can directly infect fat cells and immune cells within body fat. When that happens, researchers say, the body triggers an immune response that may contribute to a severe case of the virus.

“The bottom line is, ‘Oh my god, indeed, the virus can infect fat cells directly,’” Dr. Philipp Scherer, a scientist who studies fat cells at UT Southwestern Medical Center in Dallas, told The New York Times.

“Whatever happens in fat doesn’t stay in fat,” Scherer, who was not involved with the study, added. “It affects the neighboring tissues as well.”

Researchers found that while fat cells could be infected by the coronavirus, when immune cells in the fat tissue were also involved, a robust inflammatory response was triggered.

“It’s an aspect of COVID that hasn’t received a whole lot of attention,” Dr. William Schaffner, a professor of infectious diseases at the Vanderbilt University School of Medicine, told Insider. “The fat itself may actually become a reservoir for the virus and somehow be involved in its inflammatory response.”

The Stanford study’s senior authors, Dr. Tracey McLaughlin and Dr. Catherine Blish, found a dramatic inflammatory response happened soon after the fat tissue was infected by the coronavirus.

The results were consistent with other studies that have showed that viruses can infect fat cells, the researchers wrote.

The more fat cells a person has, the more of a reservoir for the virus to multiply, and the greater the chance an inflammatory response can trigger problems throughout the body, researchers said.

“This could well be contributing to severe disease,” Dr. Blish said. “We’re seeing the same inflammatory cytokines that I see in the blood of the really sick patients being produced in response to infection of those tissues.”

The number of obese adults in the U.S. could have contributed to greater cases of severe disease in this country, researchers said.

The United States has one of the highest rates of obesity in the world with 42 percent of its residents being obese.

According to the Centers for Disease Control and Prevention, Black adults have the highest age-adjusted prevalence of obesity at 49.6%, followed by Hispanic adults (44.8%), non-Hispanic White adults (42.2%) and non-Hispanic Asian adults (17.4%).

Researchers also suggested that obesity could contribute to long COVID-19. People with long COVID-19 have symptoms of the virus — fatigue, body aches, chest pain, or shortness of breath — that persist for months after a COVID-19 infection.