Why Exercise is Good for Your Immunity

When it comes to reducing your risk of getting sick, you can’t beat washing your hands and not touching your face. But something you already do is also helping to keep your immune system in top condition so it can better fight off all viruses: working out.

“One of the best things people can do for their immune health is to exercise most days of the week,” says David Nieman, DrPH, PACSM, professor of biology at Appalachian State University, and director of the Human Performance Labs at the North Carolina Research Campus. In fact, in one of his studies, of all the lifestyle factors they examined (including stress, sleep, and diet), exercise was number one at reducing illness.

Now, don’t be mistaken—working out in and of itself will not magically prevent or treat illness. However, regular, moderate-intensity physical activity of up to 45 minutes, five days a week, has been shown to be beneficial for immunity and is likely to help reduce the risk of respiratory infections, according to an analysis published in the journal Exercise Immunology Review in March.

What seems to happen is that when you work out, the muscle contractions and increased blood flow stimulate the function and circulation of natural killer cells, T cells, and other immune cells. “This improves their ability to detect and kill pathogens and viruses,” Nieman explains.

Two to three hours post-workout, your immune function returns to normal. However, as you continue to work out on a regular basis, the benefit adds up, making you more resilient to viruses and helping you should you fall sick.

In a study published in 2011, Nieman followed one thousand men and women for 12 weeks during the fall and winter to see if they came down with a common cold. Of those who did, the ones who worked out five or more days a week experienced a 43 percent reduction in the number of sick days compared to those who worked out no more than once a week. They also experienced less severe symptoms. Additionally, regular exercise reduces systemic inflammation and may improve immune responses to vaccination.

However, the benefit seems to max out after 45 to 60 minutes of moderate-intensity work. Longer exercise sessions and more intense activity haven’t been shown to lead to the same advantages. “When you deplete your glycogen stores with high-intensity effort that goes on for a couple of hours, and you do that every day or every other day, it reduces the supply of glycogen to immune cells, and they don’t function as well,” Nieman explains.

Also, the advice that you should never jump straight from being mostly inactive into following a demanding, highly-intense fitness program benefits your immune system too isn’t always accurate. “Everybody has to find their sweet spot,” says Nieman. If you are new or returning to exercise, “gradually get into it and find out what your body can handle without feeling tired and run down.”

Lastly, don’t follow the idea that you should “sweat it out” if you get COVID-19. “Exercise is lousy as a treatment strategy, and it’s a dangerous strategy” with COVID-19, says Nieman, since the virus makes breathing difficult.

Whatever your current fitness level, keep in mind that everybody is different. There are some elite athletes who thrive at endurance sports or can handle a higher workload than others. So if you love your long runs and feel you typically stay healthy year-round, there’s no reason to hang up your running shoes.

“The immune system needs exercise to do its job better,” says Nieman. “The result is reduced likelihood of getting sick, reduced infection days, or reduced symptom severity—so you can get out there for 30 to 60 minutes most days of the week and know you are improving the ability of your immune system to help fend off illness.”