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January 6, 2012
Exercise Can Increase or Decrease Your Chances of Catching a Cold: Intensity is Key

What if there was a way to ward off the misery of a cold? What if it had nothing to do with diet or supplements? Depending on different levels of exercise, your chances of getting the sniffles can significantly increase or decrease says Professor Mike Gleeson from Loughborough University.

The British Journal of Sports Medicine has published several research reports showing that people who are physically fit and active have fewer and milder colds.

While regular moderate exercise can reduce the risk of catching cold-like infections, prolonged strenuous exercise, such as marathons, can make an individual more susceptible. This is a topical area of research in the year of the Olympics, says Professor Gleeson talking at the Association for Science Education (ASE) Conference on Friday, on behalf of the Society for General Microbiology and the British Society for Immunology.

Upper- respiratory tract infections (URTIs) are acute infections that affect the nose, throat and sinuses, and include the common cold, tonsillitis, sinusitis and flu. Viruses that circulate in the environment usually cause URTIs. While we are constantly exposed to these viruses, it is the status of our immune system that determines whether we succumb to infection or not. Exercise can have both a positive and negative effect on immune function, combined with genetics and other external factors like stress, poor nutrition and lack of sleep. Collectively these factors determine an individual’s susceptibility to infection.

In a report on exercise immunology, published in 2003 in Current Sports Medicine Reports, David Nieman, a professor of health and exercise science at Appalachian State University noted that positive immune changes take place during each bout of moderate physical activity. Over time, this translates to fewer sick days from colds or flu, he said.

Professor Gleeson explains why the exercise factor is an interesting one. “If you have a tendency to be a couch potato then you probably have an average risk of catching an infection -- typically 2-3 URTIs per year. Research shows that those undertaking regular moderate exercise (e.g. a daily brisk walk), can reduce their chance of catching a respiratory infection, such as a cold, by up to almost a third.” This effect has been shown to be the result of the cumulative effect of exercise leading to long-term improvement in immunity. “Conversely, in periods following prolonged strenuous exercise, the likelihood of an individual becoming ill actually increases. In the weeks following a marathon, studies have reported a 2-6 fold increase in the risk of developing an upper respiratory infection,” said Professor Gleeson. “The heavy training loads of endurance athletes make them more susceptible to URTIs and this is an issue for them as infections can mean missing training sessions or underperforming in competitions.”

In another study, researchers analyzed a year's worth of health and exercise data on 547 healthy adult men and women. The study found people who were the most active had 25 percent fewer colds than people who were the least active.

Those who were moderately active also had fewer colds than people who were the least active, but the difference wasn't as striking, says Charles E. Matthews, author of the study and a research assistant professor of epidemiology at the University of South Carolina.

The researchers looked at physical activity done in the home, at work and during leisure time. They considered only moderate to vigorous exercise, including activities such as brisk walking, scrubbing floors or heavy gardening -- mowing the lawn, for instance. Vacuuming or dusting wouldn't qualify, Matthews says.

After controlling for major diseases, age, diet, having young children in the household and psychological factors such as anxiety and hostility, they found that people who were the most active had the fewest colds.

The average number of colds for the year among people in the study was 1.2.

"The most likely explanation for the finding is that higher levels of activity for the average person derive some benefits to their immune defenses against a cold," Matthews says.

The major players in this immune regulation are immune cells called Natural Killer (NK) cells which are important weapons in the fight against viral infections. NK cells recognise viral-infected cells as foreign invaders and force them to commit suicide.” During moderate exercise the activity of NK cells is enhanced, whereas stressful endurance activities such as marathons can turn down NK cell activity. These changes are tightly regulated by stress hormones and other immune cells,” explained Professor Gleeson.

There is a clear take-home message from our current understanding of the link between exercise and immune function. “Moderate exercise has a positive effect on the immune system. So to keep colds at bay, a brisk daily walk should help -- it’s all about finding a happy medium,” said Professor Gleeson.

The key is to listen to your body when you exercise. If you feel more exhausted than energized despite your best exercise efforts, it's probably time to scale back your regimen.

And finally, practice moderation. As the American Council on Exercise notes: "Don't expect to exercise an hour every day simply because your fit friend does. The body needs time to adjust, adapt and recuperate. Exercising to the point of overtraining is simply taking one step forward, two steps back."


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