Is it true that exercise strengthens the immune system?

Special to The New York Times Infobae.

(Science Times)

You’ve probably heard this tip: One of the best things you can do to stay healthy — especially as cold and flu season approaches —
is to be physically active.

This conventional wisdom has been around for a long time, but until recently researchers didn’t have much data to support such a notion. Now scientists studying risk factors associated with COVID-19 have found some preliminary clues about the link between regular exercise and better immune defense against disease.

When researchers reviewed 16 studies of people who were physically active during the pandemic, they found that exercise was associated with a lower risk of infection as well as a lower chance of suffering from complications of COVID. The analysis, published last month in The British Journal of Sports Medicine, has sparked excitement among exercise scientists, who say the findings could lead to updated physical activity guidelines and health policy that view exercise as medicine.

Experts who study immunology and infectious diseases are more cautious in interpreting the results. But they agree that exercise helps protect health through several different mechanisms.

Exercise can improve immunity in several ways.

For decades, scientists have observed that people who are fit and physically active seem to have lower rates of various respiratory infections. Also, when people who exercise do get sick, they tend to have a milder illness, said David Niemann, a professor of exercise and health sciences at Appalachian State University who was not involved in the recent COVID research.

“The risk of complications and death from the common cold, flu and pneumonia is greatly reduced,” Niemann said. “I call it the vaccine-like effect.”

The new meta-analysis, which looked at studies conducted between November 2019 and March 2022, found that this effect extended to COVID. People around the world who exercised regularly had a 36% lower risk of hospitalization and a 43% lower risk of death from COVID compared to those who were inactive. They also had a lower chance of getting COVID at all.

People who follow the recommendations for at least 150 minutes of moderate activity or 75 minutes of vigorous activity per week seem to benefit the most. But even those who exercised less were more protected against the disease than those who did nothing.

Researchers theorize that exercise may help fight infectious bacteria and viruses, for example by increasing the circulation of immune cells in the blood. In some small studies, researchers have also found that muscle contraction and movement release signaling proteins known as cytokines that help direct immune cells to find and fight infection.

Although cytokine and immune cell levels drop two to three hours after you stop exercising, Nieman explains, your immune system becomes more receptive and able to capture pathogens more quickly if you exercise every day. “Your immune system is primed and in better shape to deal with the viral load at any given time,” he said.

In healthy people, physical activity is also associated with lower chronic inflammation. Widespread inflammation can be very damaging and even cause the immune cells themselves to turn against the body. This is a known risk factor for COVID, Nieman noted. He also said it therefore stands to reason that reducing inflammation would improve the odds of fighting infection.

Research also shows that exercise can increase the benefits of some vaccines. For example, people who exercised immediately after receiving the COVID-19 vaccine appeared to produce more antibodies. And in studies of older people who were vaccinated early in the flu season, those who exercised had antibodies that lasted through the winter.

Exercise provides a number of health benefits that help reduce the frequency and severity of illness, says Stuart Ray, an infectious disease specialist at Johns Hopkins University School of Medicine. Incorporating a walk, jog, trip to the gym, or a sport of your choice into your routine is known to help reduce obesity, diabetes, and heart disease, for example, all of which are risk factors for complications from the flu and COVID. Exercising can help you get more restful sleep, boost your mood, and improve insulin metabolism as well as cardiovascular health, which improves your chances of fighting the flu and COVID. It’s hard to know, Ray says, whether the benefits come from direct changes in the immune system or simply better overall health.

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