Exercise and the Immune System

Should you avoid working up a sweat when you have the sniffles? Or is sweating it out in the gym the secret to curing the common cold?

Despite advice that a cold should be coddled, moderate exercise isn't a bad idea when you've got a runny nose. And unlike lots of other suggestions on how to treat a cold, this one has some science behind it.

Study subjects at Ball State University were infected with a cold virus and divided into two groups; exercisers and non-exercisers. With their symptoms in full bloom, the exercisers ran on the treadmill while the other group remained sedentary.

Despite the two different strategies for dealing with a cold, researchers found no difference in the severity of the symptoms between both sets of subjects. Nor was there a difference in the length of time the cold hung around. In fact, the only difference reported between the two groups was their own assessment of their cold symptoms. The exercisers felt better than those who remained sedentary.

So, if all that sneezing and sniffling is getting you down, maybe a workout - not rest, is just what the doctor ordered.

But that's not the only positive effect exercise has on a cold. Making exercise a habit may just extend the time between runny noses. Another study, this one done out of the University of South Carolina, found that regular exercisers had 20-to 30 per cent fewer colds than those who never pulled on a pair of athletic shoes. A similar study published in the British Journal of Sports Medicine reported that the number of colds among people who exercised five or more days a week was up to 46 per cent less than those who exercised only one day or less a week.

What kind of exercise works best? There's no definitive answer, but the University of South Carolina study was based on 30 minutes of walking every day, while the researchers at Ball State had their cold sufferers run 30 to 40 minutes every day for a week.

What is it about exercise that knocks colds for a loop? Scientists suggest that moderate intensity workouts boost immunity by increasing the number of natural killer cells for several hours after a bout of physical activity. These cells circulate around the body, fighting off the offending virus.

So with all that good stuff happening after a bout of exercise, surely more exercise boosts even greater immunity? Afraid not.

High volumes of exercise have the opposite effect on the immune system. Elite and endurance athletes who routinely work out for more than 90 minutes are actually more susceptible to colds than the average recreational exerciser.

Extended bouts of high intensity exercise increases the production of a stress hormone called cortisol, while decreasing the number of those same killer cells that moderate intensity boosts.

So for up to three days following an extended strenuous workout, viruses have an easier time taking hold.

This phenomenon has been well documented in marathon runners who are more susceptible to the cold virus after tackling the 42-kilometre race.

Studies have shown marathoners have six times the risk of getting a cold when compared to those who were equally as fit.

The same phenomenon was found among endurance cyclists who ride hard for three hours, three days in a row.

Also worthy of caution is exercising in sub-zero temperatures while in the midst of a cold. An already irritated throat and nose may get worse, not better, when subjected to frigid air inhaled during an extended or intense bout of exercise.

Most physicians recommend suspending exercise if the cold symptoms lie below the neck (coughing or general aches) or if a fever is present.

It's also important to pay attention to how you feel. If the last thing you want to do is exercise, go ahead and take a rest day.

As long as you keep it short and reduce your normal workout intensity you shouldn't suffer any ill effects. In fact, you may just turn the tide on a beast of a head cold that has been making you feel miserable.

So the next time you feel a cold coming on, grab your running shoes instead of a box of pills. Exercise is medicine.