Why is obesity so common in COVID-19 patients?

A hormone that connects the body's metabolism and immune response system may explain why COVID-19 is so dangerous for people with obesity.

"The problem for people with obesity is that their leptin levels are always high, and that can affect the response to a COVID-19 infection," said Candida Rebello, Ph.D., RD, lead author of a new paper that traces the link between obesity and the virus.

The hormone leptin regulates appetite and metabolism. Leptin also regulates the cells that fight infection. Leptin is produced by fat cells, and to a lesser extent by tissues in the lungs. The more fat a person has, the more leptin circulates in their body.

Elevated leptin levels hamper the body's ability to fight off infections, in the lungs and elsewhere, Dr. Rebello said. High leptin levels promote a low-grade systemic inflammatory state.

"If you have obesity, there are a number of underlying health issues that make it more difficult for you to fight off a COVID-19 infection," said John Kirwan, Ph.D., Pennington Biomedical Executive Director and a co-author of the review. "Your entire body, including your lungs, may be inflamed. Your immune response is likely compromised, and your lung capacity reduced.

"Add in a virus that further weakens the body's ability to fight infection, that can limit the body's ability to control lung inflammation, and you have the recipe for disaster."

COVID-19 vaccine developers should take the immunocompromised state resulting from obesity into consideration, in much the same way they would advancing age.

The researchers say the role of leptin in COVID-19's development bears investigation along with the viral proteins that alter the immune systems of people with obesity. One potential avenue of treatment may be a drug that prevents inflammatory responses to the virus.

Another potential avenue of investigation includes examining how proinflammatory fat tissue in people with obesity might contribute to activating fewer infection-fighting cells and why those cells die more quickly.