Be it a brisk walk on the treadmill or a dip in the pool, exercise has been linked to everything from a better night’s sleep to improved brain function. And research has found that it might be a literal cure-all, helping protect your body against disease over the course of your life. In fact, a single sweat session mobilizes your immune system, calling your first line of defense into action against everything from the common cold to cancer.
“The immune system is tasked with keeping us healthy,” says exercise immunology researcher David Bartlett, Ph.D., an assistant professor of medicine at Duke University Medical Center. “This can be by the protection from—and timely resolution of—infections and infectious diseases, the detection and removal of malignancies, and responses to vaccines”.
The immune system is distinct in that it’s not static, meaning its level of function is subject to change, for better or for worse. For instance, it loses steam with age. “When exposed to the same challenge, cells of the aged immune system do not respond as well as cells from a young person,” says Bartlett. That’s not the only factor: studies have found that stress can blunt the immune system response; the same goes for a lack of sleep.
On the other hand, other things can improve your immune system — like exercise. Your body responds to movement. “When you exercise, the heart rate and blood pressure go up, and then different chemical messengers are released,” explains exercise immunology researcher David Nieman, Dr.PH., a professor of biology at Appalachian State University and director of the Human Performance Lab at the North Carolina Research Campus.
“All of that results in immune cells being released in greater-than-normal quantities from what we call peripheral lymphoid tissues—areas that the immune cells typically reside in—which start coursing through the body at a higher rate than normal”.
And your immune system doesn’t flood your body with just any cells—which, by the way, are not created equal. “The best types of immune cells are released during exercise,” says Nieman. “We’re talking about special types of natural killer cells; they’re like the Green Berets of the immune system.”
Along with your natural killer cells (or NK cells), which destroy cancer cells and cells infected with a virus, come the T cells, a type of cell that generates a “memory” of infection or antigen.
That recognition can have a big payoff. “When you encounter an infection you previously had, memory T-cells can respond much more quickly and effectively than when you first had the infection,” says Barlett.
“Therefore, if you can boost the number of T cells, that will improve memory responses — which translates to an improved ability to protect you.” Essentially, every time you work out, you create a stockpile of these protective cells ready to fight off viruses, bacteria and beyond.
T cells and NK cells aren’t the only pieces of the puzzle. B cells, which produce antibodies, can also create memories, and they are similarly generated during exercise — so it’s very much a team effort. The combination can help max out your protection.
“When these are optimal, they work efficiently together,” says Bartlett. “When even one cell type is not functioning optimally, there is a detrimental effect.”
This optimization can have major implications for your health. “As the days go by, you have what we call enhanced surveillance against pathogens,” says Nieman. “In randomized trials and in large studies where we follow groups of people [who exercise regularly], the reduction in the number of sick days is up to 50%—and it’s against all sorts of diseases.”
Exercise can also aid in the treatment of cancer, which is notorious for its ability to turn off immune cells. Bartlett compares the effect of exercise to recent immunotherapy treatments. “Immunotherapies increase the function of the immune system by effectively taking off the brakes that have been applied by the tumor,” he explains.
“Exercise training can promote a similar response, whereby the immune system changes and becomes better capable of killing tumor cells. In a way, exercise training is a type of immunotherapy — but with no significant harmful side effects.” He’s found that people who are more physical have a lower risk of developing cancer, and that they also tend to fare better during and after cancer treatment.
That said, as with most things in life, moderation is key. “Early researchers found that very high levels of exercise training could lead to increased infections, such as colds occurring after marathon running,” says Anne McTiernan, M.D., Ph.D., a professor at Fred Hutchinson Cancer Research Center in Seattle.
“However, those runs were also conducted in close proximity to many other people, so it’s not clear if it was the training or the crowding that caused the infections.”
When you hit 90 minutes or more of intense exercise, “red flags are starting to go off all over the body,” says Nieman. “All of that stress is reflected by the immune system, and it just starts getting a bit dysfunctional.
Then, the longer you keep going, the more you can see this immune dysfunction.” Fortunately, most people are able to recover with enough rest and nutrition, so consider this a good reason to take a rest day.
Just as more is not necessarily better, exercise also isn’t really a prescriptive tool. Rather, its benefits are largely preventative. “It’s like a summation effect, where you have to keep doing it day after day to get this protective effect,” says Nie-man.
“But exercise is not recommended like a drug to treat infections.” Going for a walk won’t really do much when you have the flu — and it could make you feel worse or prolong your illness by stressing the body.
Those preventative benefits, however, become critical as we age. “Older people have poor immune functions, are at increased risk of diseases and are generally less physically active,” Bartlett says.
Regular exercise seems to be a good solution. In fact, it can even slow down the effects of the aging process — for your immune system, at least. “When you compare the immune system of healthy older adults to an older adult who is considered a master athlete — meaning they exercise regularly and typically compete in competitions — the master athlete’s immune system looks like that of someone 20 years younger,” says Bartlett.
Not that you have to be a master athlete: even if you double the number of steps you take every day — to 10,000 steps from 5,000, for example — your immune system will work better, and more like that of a younger person.
If, as the saying goes, an ounce of prevention is worth a pound of cure, then exercise should be a part of your daily life. Here’s how to integrate it effectively and safely.
1. Know the Guidelines
A single walk around the block might not cut it. The current physical activity guidelines in the U.S. recommend either 150 to 300 minutes of moderate-intensity exercise or 75 to 150 minutes of vigorous exercise, plus an additional two days of strength training, every week for the rest of your life. You may reap additional health benefits by going above and beyond that threshold (at a safe intensity level, of course). Intimidating? Maybe. But simply knowing the recommendations can help you plan accordingly.
2. Create a Plan
Speaking of plans, having one will help, especially if you’ve tried and failed to stick with regular exercise in the past. “Park your car as far from the office or mall as possible, stop using the elevator, or every time commercials are on TV, get up and walk around the house until your program resumes, ”Bartlett suggests. And be prepared to adapt to challenge yourself more. For instance, once you’re in the habit of walking a certain number of steps a day, set new goals or try to speed up your pace.
3. Keep It Consistent
In a 2006 study published in the American Journal of Medicine, women between the ages of 50 to 75 stuck to a moderate-intensity exercise program — think walking on the treadmill, using a stationary bike or walking outdoors — for 45 minutes a day, five days a week, for a full year, while a control group just stretched. “Women in the exercise program reported fewer cold symptoms than did controls,” says McTiernan, a lead author of the study. (That clocks in at 225 minutes a week of moderate-intensity exercise, which is well within the guidelines.)
4. Take a Stand
Even if you’re regularly putting in time at the gym or outdoors, how you spend the rest of your day matters too. “It’s not just putting in your exercise minutes, like a brisk walk; it’s also not allowing yourself to just sit for hours and hours,” says Nieman. “There’s new data showing that sitting for long periods of time can override the physical activity benefits.” Set an alarm for yourself to stand and stretch your legs every hour or so.
5. Split It Up
Consider divvying up workouts throughout the day. “Every time you exercise, immune cells are stimulated into greater activity,” explains Nieman. So splitting up your routine between morning and evening — even just a post-dinner walk—can help stimulate two cascades of immune reactions instead of just one from a single workout.