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Infectious Diseases

Updated 05 August 2020

Why can Covid-19 be so dangerous where patients are obese?

It is established that obesity can increase the risk of severe Covid-19. Now, new research points to a hormone that regulates the appetite and immune system.

  • Leptin is a hormone that regulates appetite, but also affects the body's ability to fight infection.
  • An excessive amount of leptin could have an inflammatory effect, causing more severe Covid-19.
  • The new research aimed to highlight the link between obesity, Covid-19 and leptin overproduction.

As experts learn more about Covid-19, the disease caused by SARS-CoV-2, it is now known that some comorbidities increase the risk of more severe disease.

One of these risk factors that makes patients more susceptible to severe Covid-19 is obesity – a body mass index higher than 25.

Previous research published on Health24 already established that obese patients were more likely to develop blood clotting in the lungs, leading to respiratory distress and even death. But now, the Pennington Biomedical Research Centre is looking at what could be the culprit: high levels of the hormone leptin.

What is leptin?

Leptin is a hormone that is released from fat cells in adipose tissue. This hormone sends signals to the hypothalamus in the brain to help regulate hunger and long-term food intake and the way the energy from that food is used. Basically, leptin helps us to maintain our body weight.

People who are obese have unusually high levels of leptin, as the brain does not always respond to the hunger queues released from the hormone. When there are already excess fat stores in the body, the body may become resistant to leptin, which causes the fat cells to produce even more leptin in the same way insulin resistant people overproduce insulin.

Leptin and infection in the body

Leptin is also known to regulate the cells in the body responsible for fighting infections – and elevated leptin levels can hinder the body's ability to fight off infections.

According to Candida Rebello, the lead author of the study published in the International Journal of Obesity, the way these unusually high levels of leptin affect the body to fight infection can be an explanation of why severe Covid-19 may be linked to obesity. High levels of leptin can cause a low-grade inflammatory state in the body.

"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," states John Kirwan, PhD, Pennington Biomedical executive director and a co-author of the review in a news release. "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."

What this research could mean for Covid-19 management

The researchers suggest that developers of Covid-19 vaccines should investigate the role of leptin along with the viral proteins that alter the immune system in patients with obesity.

They also suggest that a potential treatment could include a drug that prevents any inflammatory response from SARS-CoV-2.

The researchers also suggest that more research be done on how proinflammatory fat tissue in people with obesity causes the body to activate fewer infection-fighting cells and how this can be avoided.

READ: Obesity and Covid-19: Researchers find major risk for deadly blood clots in the lungs

READ: Obesity ups odds for severe Covid-19 in younger patients

READ: Overweight COPD patients at higher risk of Covid-19

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