How Exercise Affects Immunity

Movement helps your body’s immune system function better, but you can overdo it.

Exercise and immunity in the human body apparently work on a J curve, meaning upper respiratory immunity increases with moderate exercise but decreases with intense exercise, especially without breaks for rest. 

But, generally, if you exercise regularly and are fit, you are less likely to catch a cold during the winter months, according to one study. 

Those in the top quarter for fitness levels (who did five or more days of exercise a week) experienced 43 percent fewer days with upper respiratory tract infection symptoms than those in the lowest 25 percent of fitness levels (who did one day or less of exercise).

And when those who exercised did get cold symptoms, the symptoms were less severe. Upper respiratory tract infection symptoms were 32 percent less severe in the top 25 percent of exercisers compared to the bottom 25 percent.

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The precise nature of the link between exercise and increased immunity is still a mystery, but it could be that each round of exercise causes a “transient increase in immune system activity,” increasing the numbers of white blood cells and immunoglobulin in your blood, which in turn reduces your susceptibility to disease, the researchers suggest.

"As a general rule the healthier you are, the easier you'll find it is to fight off infections," says associate professor Stephen Turner, from the Department of Microbiology and Immunology at the University of Melbourne.

The effect may be hormone-mediated, he says. "We know that people who exercise regularly have lower levels of stress hormones in the blood, and there's a definite link between low levels of stress hormones and improved immunity." 

Another study found that a large number of the immune T cells in cancer survivors improved their ability to fight against disease after they participated in an exercise class for 12 weeks

“What we’re suggesting is that with exercise, you might be getting rid of T cells that aren’t helpful and making room for T cells that might be helpful,” study researcher Laura Bilek, of the University of Nebraska Medical Center, said. “If exercise indeed strengthens the immune system and potentially improves cancer surveillance, it’s one more thing we should educate patients about as a reason they should schedule regular activity throughout their day and make it a priority in their lives.”

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Several recent studies, on the other hand, have found that overdoing it can weaken the immune system. One study of elite soccer players found that intense workouts reduce the level of immunoglobulin A (IgA), an antibody that prevents microbes from entering the body’s tissues and bloodstream. 

The same was found in noncompetitive athletes when they had intense workouts on consecutive days without allowing time for recovery, according to Gabe Mirkin, MD, a sports medicine doctor and author. 

“Your immunity is lowered by taking too many consecutive intense or very long-duration workouts, not taking enough rest periods, and not stopping a workout when your muscles burn and hurt or you feel excessively tired,” Mirkin says. 

So, more isn’t necessarily better. Still, physical activity may lessen your chances of upper respiratory infections and severity of symptoms if you do get a cold, according to Jeffrey A. Woods, PhD, director of the Center on Health, Aging, and Disability at the University of Illinois at Urbana-Champaign. 

Moderate exercise may offer those benefits by reducing inflammation in the body, Woods says. “So aim for at least 30 minutes of moderate aerobic exercise — such as brisk walking, cycling, swimming, or jogging — or working out on a treadmill three to five days per week,” writes Catherine Winters. 

Moderate exercise improves blood flow through your cardiovascular system, helping to flush toxins and germs from your body through the excretory system via urine and sweat, adds Matthew David Hansen, in IG Living magazine. Increased blood flow also keeps the antibodies and white blood cells needed to fight infection circulating rapidly as a possible early defense against transient microbes. 

“Regular moderate exercise appears to have a cumulative effect that leads to a more permanently improved immune response, and again, the benefits seem to be accessible to nearly everyone, regardless of their personal immune status or history,” Hansen writes. 

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