Can exercise boost your immunity?  Yes, but overexercise might reduce it

Can exercise boost your immunity? Yes, but overexercise might reduce it

You’ve probably heard the advice: one of the best things you can do to stay healthy – especially as cold and flu season approaches – is to stay physically active.

This folk wisdom has been around for ages, but until recently, researchers didn’t have much data to support this idea. Now scientists studying risk factors for Covid-19 have found preliminary evidence linking regular exercise to better immune defenses against the disease.

When researchers looked at 16 studies of people who stayed physically active during the pandemic, they found exercise was associated with a lower risk of infection as well as a lower likelihood of severe Covid. The analysis, published in the British Journal of Sports Medicine, has generated a lot of excitement among exercise scientists, who say the findings could lead to updated guidelines for physical activity and health policy that will s revolve around exercise as medicine.

Experts who study immunology and infectious diseases are more cautious in their interpretation of the results. But they agree that exercise can help protect health through several different mechanisms.

Exercise could boost immunity

For decades, scientists have observed that physically fit and physically active people seem to have lower rates of several respiratory tract infections. And when people who work out get sick, they tend to have less severe illness, said David Nieman, professor of health and exercise sciences at Appalachian State University, who was not involved. to the recent Covid review. “The risk of serious consequences and mortality from colds, flu, pneumonia – they’re all knocked down a bit,” Prof Nieman said. “I call it the vaccine-like effect.”

The new meta-analysis, which looked at studies between November 2019 and March 2022, found that this effect extends 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 than those who were not active. They also had a lower likelihood of contracting Covid at all.

People who followed the guidelines recommending at least 150 minutes of moderate activity or 75 minutes of vigorous activity per week seemed to experience the most benefit. But even those who exercised less were better protected against disease than those who didn’t exercise at all.

Researchers theorize that exercise can help fight infectious bacteria and viruses by increasing the circulation of immune cells in your blood, for example. In some small studies, researchers have also found that contracting and moving muscles release signaling proteins called cytokines, which help immune cells find and fight infections.

Even though your cytokine and immune cell levels drop two or three hours after you stop exercising, Prof Nieman said, your immune system becomes more responsive and able to catch pathogens faster over time. if you train every day. “Your immune system is primed and in better shape to deal with a viral load at all times,” he said.

In healthy humans, physical activity has also been associated with reduced chronic inflammation. Widespread inflammation can be extremely damaging, even turning your own immune cells against your body. It’s a known risk factor for Covid, Prof Nieman said. Therefore, it makes sense that reducing inflammation could improve your chances of fighting infection, he said.

Research also shows that exercise can amplify the benefits of certain vaccines. People who exercised right after receiving their Covid-19 vaccine, for example, seemed to produce more antibodies. And in studies of older adults who were vaccinated at the start of flu season, those who exercised had antibodies that lasted through the winter.

Exercise provides a host of broader health benefits that can help reduce the incidence and severity of disease, said Dr. Stuart Ray, an infectious disease specialist at Johns Hopkins University School of Medicine. Incorporating a walk, jog, gym session or sport of choice into your routine is known to help reduce obesity, diabetes and heart disease, for example, which are all risk factors for severe flu and Covid. Exercise can help you get more restful sleep, improve your mood, and improve your insulin metabolism and cardiovascular health, improving your chances against the flu and Covid. It’s hard to know, Dr. Ray said, whether the benefits come from direct immune system changes or just better overall health.

Research can’t tell us much

Dr Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, agreed that more research was needed before scientists could pinpoint a specific mechanism or causal link. In the meantime, he says, it’s important not to believe it too much. “Right now you can’t say, ‘I’m going to go to the gym to avoid catching Covid,'” Dr Chin-Hong said. The problem with studying the precise effect of physical activity on immunity is that exercise isn’t something scientists can easily measure on a linear scale, Dr. Ray said. “People exercise in different ways.”

Study participants usually self-report the amount and intensity of their exercise, which can often be inaccurate. And just expecting exercise to be beneficial can provide a powerful placebo effect. As a result, it can be difficult for researchers to say exactly how much exercise or what type is ideal for immune function. It’s also entirely possible that people who exercise regularly share other attributes that help them fight infections, such as a varied diet or better access to medical care, Dr. Ray said.

Beyond that, “there’s a huge debate about whether too much exercise makes you more susceptible to infection and disease,” said Richard Simpson, who studies exercise physiology and immunology at the University of Arizona.

Marathon runners often report getting sick after races, Simpson said, and some researchers believe that exercising too vigorously could inadvertently overstimulate cytokines and inflammation in the body. Exercising without a break also depletes the body’s glycogen stores, which for some people could lead to impaired immune function for a few hours or days, depending on their baseline health, he said. he declares. And training in groups or participating in intense sports training camps could expose athletes to more pathogens. Other experts point out that physically active people might just keep track of their health more closely.

Still, for the average user, early evidence suggests there may be a protective effect against serious illness. But those who struggle to get enough exercise or can’t exercise at all for whatever reason shouldn’t despair, Dr. Ray said. “What helps one person stay healthy over another is a complex mix of factors,” he said. – This article originally appeared in the New York Times

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