Even if your levels of cytokines and immune cells taper off two or three hours after you stop exercising, Dr. Nieman said, your immune system becomes more responsive and able to catch pathogens faster over time if you work out every day. “Your immune system is primed, and it is in better fighting shape to cope with a viral load at any given time,” he said.
In healthy humans, physical activity has also been linked to lower chronic inflammation. Widespread inflammation can be extremely damaging, even turning your own immune cells against your body. It is a known risk factor for Covid-19, Dr. Nieman said. Therefore, it makes sense that reducing inflammation could improve your chances of fighting off infection, he said.
Research also shows that exercise may amplify the benefits of some vaccines. People who worked out right after getting their Covid-19 vaccine, for example, seemed to produce more antibodies. And in studies of older adults who were vaccinated early during flu season, those who exercised had antibodies that lasted throughout the winter.
Exercise provides a slew of broader health benefits that may help reduce the incidence and severity of disease, said Dr. Stuart Ray, an infectious diseases specialist at Johns Hopkins University School of Medicine. Building a walk, jog, gym trip or sport of choice into your routine is known to help reduce obesity, diabetes and heart disease, for example, all of which are risk factors for severe influenza and Covid-19. Working out can help you get more restful sleep, boost your mood and improve your insulin metabolism and cardiovascular health, improving your chances against the flu and Covid-19. It’s hard to know, Dr. Ray said, whether the benefits come from direct changes to the immune system or just overall better health.
The research can only tell us so 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 said, it’s important not to put too much faith in it.
“For now, you can’t say, ‘I’ll go to the gym so that I can prevent getting Covid,’” Dr. Chin-Hong said. The problem with studying the precise effect of physical activity on immunity is that exercise is not something that scientists can easily measure on a linear scale, Dr. Ray said. “People exercise in many different ways.”
