A jogger passes two women napping on the National Mall near the U.S. Capitol. Regular exercise may reduce the chance of getting a cold.
There's always somebody passing around a cold virus -- whether it's a stranger who sneezes in the elevator or a sick colleague who lends out a pen covered in germs. But not everyone who gets exposed to a common-cold virus goes on to get sick.
"Think about a household when one person gets sick," says Ron Turner, a cold researcher at the University of Virginia. "Only about 30 percent of contacts in a household will actually develop an infection."
So, how can people cut their chances of landing in that 30 percent? Researchers say there is one cold-fighting strategy that lots of us could take advantage of: stepping up daily exercise.
More Exercise, Less Sickness?
The latest study to find benefit from daily exercise was published this month in the British Journal of Sports Medicine. Researchers recruited about 1,000 volunteers between age 18 and 85 to complete a daily log of symptoms throughout cold and flu season
"Everything from runny nose, sore throat, coughing, fever, headaches," says researcher David Nieman of Appalachian State University.
Dr. David Nieman, an exercise immunologist at Appalachian State University and a runner of more than 58 marathons and supermarathons, has been studying endurance athletes' immune systems for decades. He has found that the chance of marathoners getting sick after running their race is nearly six times higher than people who are equally fit.
After about 90 minutes of intense exertion, Nieman's tests on athletes show that stress hormones go up, muscle breaks down, and inflammation kicks in. "There's a window of about a half a day or day where viruses can multiply at higher rate because defenses are down," he says.
Marathoners aren't alone in this: The key, he says, is any high-intensity, unrelenting exercise. He's also looked at cyclists who ride hard for three hours, three days in a row and then have high infection rates. "Humans have done manual labor for centuries, and that’s what the body is used to," says Nieman. "It's only a recent phenomenon that we started going all out."
Is there any hope for endurance athletes to beat colds after races? Nieman and colleagues received funding from the U.S. Army to develop immune-boosting supplements for soldiers engaged in heavy, long battles. He's most optimistic about quercetin, a phytochemical and antioxidant found in a number of fruits and vegetables. In a 2009 study, Nieman gave cyclists 1000 mg of quercetin per day (plus a few other supplements) for two weeks before a race. Those athletes had significantly fewer illnesses following the race than those taking a placebo.
-- Eliza Barclay
At the end of the three-month study, the researchers found that the more the participants exercised, the less they reported getting sick. Those who exercised five days a week for 20 minutes or more experienced about 40 percent fewer days of illness compared with those putting in less than one day a week of activity.
"It takes getting out most days of the week to see an actual benefit," Nieman says.
Another study conducted at the Fred Hutchinson Cancer Research Center in Seattle tracked what happens when older, sedentary women start walking five days a week, and it found similar benefits.
Researchers are not certain how exercise may help prevent colds, but Nieman theorizes that aerobic activity helps recruit a bunch of important immune cells that normally "camp out" in different places in the body, such as the spleen, bone marrow or lymph nodes.
"With exercise, these cells come out and start to recirculate through the body at a higher rate," Nieman says. "They're like the Marine Corps or Special Forces that get out there and poke holes in cells that may have viruses in them."
Researchers are not all convinced by Nieman's study. "Not that I would want to discourage anyone from exercising," says Turner, of the University of Virginia. But he says there may be other reasons that some of us are more susceptible to the common cold. For instance, genes may play an important role.
Stress And Sleep Play A Role
Studies show a few other factors may pay a role in cold virus susceptibility.
Part of the story seems to be sleep. A comprehensive study by Carnegie Mellon University researchers found that when people are sleeping poorly, they're significantly more likely to catch a cold.
"People who slept less than 7 hours were 2.9 times more likely to get sick than people who slept 8 or more," says Sheldon Cohen, a professor of psychology at Carnegie Mellon.
The risk of getting the common cold also seems to be tied to stress. None of us can rid ourselves of all of life's little stressors, but the research suggests long durations of stress wear us down.
"Chronic, ongoing enduring problems, such as being in a bad marriage, having a lousy job are related to greater risk," Cohen says.
But if exercise, less stress and more sleep can cut your risk -- even a little -- they could be three more benefits of striving for a healthy lifestyle.