Striking a balance

While exercise appears to be useful in keeping colds at bay, too much of a good thing can backfire, according to scientists preparing for the next summer Olympics in London.

Exercise can significantly decrease your chances of catching a respiratory infection — but if you go too far and wear your body down, it can also increase the chances you’ll get sick, says the British Society for Immunology.

At issue are upper-respiratory tract infections (URTIs), acute infections that affect the nose, throat and sinuses, and include the common cold, tonsillitis, sinusitis and flu. Generally, URTIs are caused by viruses that circulate in the environment. While we are constantly exposed to these viruses, the state of our immune system 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.

While regular moderate exercise can reduce the risk of catching cold-like infections, prolonged strenuous exercise, such as training for marathons, can make an individual more susceptible.

“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 such as taking a daily brisk walk, can reduce their chance of catching a respiratory infection, such as a cold, by up to almost a third,” says says Prof. Mike Gleeson from Loughborough University. 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,” he says. “The heavy training loads of endurance athletes make them more susceptible to URTIs.”

There is a clear take-home message here, he says. Staying indoors during cold and flu season will work against your family, especially you are couch potatoes. So get out the stroller or sled, snap on the dog’s leash, take the children and the spouse by the hand, and head outside for a bit. “Moderate exercise has a positive effect on the immune system. To keep colds at bay, a brisk daily walk should help,” Gleeson says. “It’s all about finding a happy medium.”