Sweating Out Cold Season

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WATCH Fight Off the Common Cold With Exercise

To avoid catching a cold this season, ditch the hand sanitizer and lace up your walking shoes instead. This is the advice from investigators whose brand new British Medical Journal study found that regular exercise can reduce your chances of getting sick this winter by almost half.

Researchers from Appalachian State University in North Carolina tracked the lifestyle habits and respiratory health of 1,000 adults for 12 weeks during the fall and winter of 2008 by asking them to fill out extensive questionnaires detailing the factors that affect the workings of the body's immune system as well as how often they felt under the weather.

The study was unique because, unlike most previous work, it included people from all walks of life: Six in10 were women, and 4 out of 10 were between the ages of 18 and 39; 40 percent were middle aged, and one in four were seniors. Participants came from a wide range of backgrounds, marital status and income levels, too.

People who reported working out five days a week or more for at least 20 minutes were sick 43 percent less often than their out-of-shape peers -- and that percentage rose to 46 percent if they also perceived themselves as being fit. Severity of symptoms fell by 41percent among those who felt the fittest and by 31 percent among those who were the most active.

Even after taking into account all of the other influences that might contribute to the sniffles such as diet, sleep and stress, feeling fit and being consistently active had the biggest influence on how often people caught colds. Being older, male and married also jumped out of the data as health boosters, but to a lesser degree.

"Activity is, by far, the most powerful lifestyle habit in terms of your ability to avoid getting sick," said David Nieman, the study's lead author. "Exercise is the one thing you can do that truly seems to boost immunity. In many ways, it's more effective than hand washing and other hygiene habits. No matter how clean you are, coming into contact with viruses and bugs is unavoidable."

Exercise May 'Train' Immune System to Fight Off Colds

Nieman likened the effect aerobic exercise has on the body's immune response to an army that stages regular raids and then returns to the barracks afterwards.

"Each exercise session sparks a temporary rise in immune system cells circulating around the body," he said. "So, although these levels fall back into the normal range within three hours or so, each bout enhances the surveillance of harmful viruses and bacteria. Repeated often enough, this reduces the number and severity of infections like the common cold."

That said, too much of a good thing can turn into a bad thing. Nieman's research on marathon runners found those who log 60 miles or more per week have double the average number of illnesses and the risk of coming down with a cold or upper respiratory infection spikes six times higher the week after a race -- regardless of whether you cross the finish line first or you're a back-of-the-packer. Neiman even speculated that too much high intensity training and racing over a long period of time might lead to cancer.

So where's that fine line between protection and vulnerability?

"The threshold seems to be that the immune system stress response remains pretty good up to around 75 to 90 minutes of high intensity, unrelenting activity," Nieman said. "After that point, the muscles begin running low on fuel, stress hormone levels rise sharply and you begin to see every type of cell in the body mount a stress and dysfunction response."

But since most Americans aren't in danger of going overboard with their workouts, physical activity can be a cheap, easy defense against the common cold. And while it's true you can't stop what germs you encounter, Nieman said it's still a good idea to keep your hands clean.

Do any exercise aficionados out there care to share their experience with exercise to ward off illness? Or do you disagree with the whole connection between fitness and staying cold-free? Post your comments below.