Some people love to exercise (don’t you just hate them!). Others do it because they want to get fit and look good poolside. Still others loathe any excess movement and respectfully refrain from working out. Think about which category you fall into. Now think about this: People who don’t exercise regularly take twice as many sick days as those who do — and that’s not because they’re playing hooky! A yearlong study by the Fred Hutchinson Cancer Research Center showed that 30 minutes of moderate exercise a day cut the risk of colds in half — and increased immunity over time. By the end of the study, exercisers were three times less likely to get sick. Now if someone were to ask you which you’d rather, a half-hour walk at lunchtime or a weeklong cold, call us psychic, but we bet we know which one you’d choose.
Maybe the risk of a cold isn’t the thing that’s going to get us up and running. What most of us want to prevent is the other C-word: cancer. According to John J. Ratey, MD, clinical associate professor of psychiatry at Harvard Medical School and author of Spark: The Revolutionary New Science of Exercise and the Brain, being a couch potato is the most consistent risk factor for cancer. He notes that physically active people have a 50 percent lower chance of getting colon cancer. What’s more, a study by the National Cancer Institute shows regular exercise yields a 23 percent lower risk of breast cancer.
Exercise boosts our resistance to viruses and infections by stimulating the release of immune cells into our bloodstream. These cells hunt down foreign invaders. “You want to have a good amount of immune cells in circulation, so if there’s an attack they can mobilize to the area,” explains Brian McFarlin, PhD, associate professor of exercise physiology, nutrition and immunology at the University of Houston.
These cells are “the upfront marine corps of the immune system,” says David Nieman, DrPH, FACSM, director of the Human Performance Lab at Appalachian State University and vice president of the American College of Sports Medicine. “When they circulate at a higher rate than normal, their ability to detect and deal with pathogens (the bad guys) is improved.” This troop-rallying response kicks in minutes after you start exercising and lasts for one to three hours afterward. Though the benefits are short-lived, exercising daily has a cumulative effect that keeps the immune system primed.
You don’t have to be an elite athlete, either. Dr. Nieman’s research has found that walking briskly for 30 to 40 minutes five days a week lowered the number of colds people got by 40 percent.
“Walking for 30 to 45 minutes most days of the week is just the right amount to boost health, improve fitness, reduce sick days and enhance your immune surveillance,” Dr. Nieman says. Of course, you can also maximize your resistance to colds, cancer and everything in between with other kinds of moderate exercise. Moderate being the key word. Vigorous training exhausts more than your muscles; it can weaken your immune system as well. “We as humans think if x is good, 10x is better, and it just doesn’t work that way,” Dr. Nieman says. Marathon runners, for instance, are six times as likely to get sick after a race, he notes.
So, could overdoing it at the gym make us more susceptible to infections? Probably not. “You have to get 90 minutes of high-intensity exercise or more before the immune system goes down in function. People can go out [running] for 30, 45, 75 minutes, and all of that is within the realm of immune enhancement,” Dr. Nieman says.
Burn Off Stress
Something else that can wipe out our reserves is chronic stress. It’s probably no coincidence that, after a rough couple of weeks at work, you feel run-down. According to a study in the Journal of the American Medical Association, the effects of long-term stress on the immune system and inflammation process may influence depression, infections, autoimmune diseases, heart disease and even some types of cancer. While it is not completely understood how, studies show that the more a person exercises, the more capable she is of handling psychological stress. Working out regularly also helps build self-esteem, which can make you feel more capable of handling life’s challenges — and less ruffled.
“We can’t change our world,” says Monika Fleshner, PhD, a professor in the Department of Integrative Physiology at the University of Colorado at Boulder, who has been studying the effects of stress and exercise on rats. “So what we’ve been investigating is how to change the body’s reaction to stress.” What she’s learned: Maintaining regular exercise can keep stress from weakening our immune system. After a doozy of a day or even a fight with your spouse, a short walk or run may just be your best antidote against stress and sickness.