Medical science still has not figured out how to cure the common cold, but the folks in the white coats may have discovered how to avoid it.
Moderate exercise, the kind recommended to reduce the risk of heart disease and other serious ailments, now looks to be a powerful weapon in the everyday battles against colds and flus as well.
Despite all the clamor about how exercise is good for you, until the late 1980s researchers had done few studies on how it affects the immune system. They had looked at marathoners and other highly trained athletes and noted a tendency to catch colds after a major competition. (Jocks call it overtraining.) But nobody knew what happened during the more laid-back exercise practiced by the rest of us - a walk, a bike ride, an aerobics class.
Then along came David Nieman, a public health researcher at Appalachian State University in Boone, N.C. In 1989, Nieman tested women in their 30s and found that those who walked briskly for 45 minutes a day, five days a week, were sick with colds for only five days during the 15-week study period. Their sedentary peers, on the other hand, sported colds and flus of one kind or another for 10 days. The study was conducted during peak cold season.
Four years later, encouraged by his original results, Nieman rounded up women in their 60s, 70s and 80s, and set half of each group to walking 37 minutes a day, five days a week, for 12 weeks. He found that 50 percent of the control group caught colds, while only 21 percent of the walkers did. Among the women who had been dedicated exercisers before the study began, only 8 percent fell ill - not a bad percentage for an age group whose immune powers are generally on the downswing.
Exercise, it seems, revs the immune system into high gear. Within minutes of beginning an activity, an exerciser’s white blood cells - the body’s first line of defense against invading organisms - increase in number. The count returns to normal within a few hours, but that temporary boost seems to either clear out germy intruders or make the immune system more efficient at repulsing them throughout the day.
“If you work out daily, on a moderate to strenuous basis, there’s good reason to believe you’ll be sick less often,” Nieman says.
You can get too much of a good thing, however. Marathoners and other extreme exercisers push their bodies to the point where muscle fibers break down. The immune system then mobilizes to clean up the broken muscle fragments, releasing the stress hormones cortisol and epinephrine in the process.
Even people with chronic illnesses may benefit from moderate exercise. In a study conducted by Arthur LaPerriere, an associate research professor at the University of Miami School of Medicine, people infected with HIV who rode exercise bikes for 45 minutes, three times a week increased their CD4 cell count - the chief yardstick for health in AIDS patients. They also reported less anxiety and depression, feelings that LaPerriere believes can weaken the immune system.
“It’s not clear exactly how it works on the cellular level,” LaPerriere says, “but we’re looking into a variety of mechanisms to figure it out.”
Regular exercise also seems to stave off the decline in immune function that researchers used to think was an inevitable part of aging. Usually T cells lose 50 percent of their power by the time a person reaches her 70s (T cells kill virus-infected and foreign cells).
In Nieman’s studies, however, the 65-year-olds who had made fitness a way of life boasted T-cell counts as high as those of people in their 30s.