Why is COVID-19 so dangerous for the obese? Study points to hormone ‘leptin’

BATON ROUGE, La. — Overweight and obese individuals are at an especially high risk of developing severe, life-threatening COVID-19 symptoms. But, why exactly is that the case? A new study from Louisiana State University offers up a strong theory.

Researchers say the connection between obesity and severe COVID-19 symptoms may be a specific hormone that controls appetite, metabolism and the immune system.

“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,” explains lead study author Candida Rebello, PhD, RD, in a release.

What is leptin?

The hormone in question, leptin, which helps regulate both appetite and metabolism. But, that’s not all; leptin also controls infection-fighting cells. Now, leptin is produced in the first place by fat cells themselves (and lung tissues to a lesser degree). In short, the more fat a person carries around, the more leptin flows throughout their body.

According to the study’s authors, high bodily leptin levels can seriously impede a person’s ability to fight off infections, particularly in the lungs. Moreover, such levels foster a state of low-grade systemic inflammation.


“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,” says study co-author John Kirwan, PhD, Pennington Biomedical Executive Director.  “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,” he adds.

More focus on COVID-19 and obesity

Researchers say that the detrimental effect obesity has on the body’s immune system strength should be in the minds of coronavirus vaccine developers, the same way old age is always a factor for vaccine scientists.

Overall, the authors think more research focusing on the relationship between leptin and COVID-19 is necessary. They want to investigate the specific viral proteins that change obese peoples’ immune systems.

Such research may conceivably produce new ways to better protect overweight individuals from the coronavirus. For example, one possible treatment avenue would be a drug that blocks inflammatory responses to the virus.

Finally, the study’s authors think it would be beneficial to investigate if pro-inflammatory fat tissues within obese people cause fewer infection-fighting cells to activate, and then die at a quicker pace, in the event of a COVID-19 infection.

The study is published in the International Journal of Obesity.

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