Can Exercise Increase Your Risk of Colds and Flu?

Regular exercise offers a variety of health benefits from building a stronger, more conditioned heart to easier weight management; but what about the effects of exercise on the immune system? Some runners and athletes report getting more colds and viruses during the periods when they exercise most intensely. Does exercise decrease immunity and make catching a cold or the flu more likely?

The good news is that moderate exercise doesn’t appear to decrease immunity. In fact, regular, moderate exercise such as fast walking, aerobics, bicycling and jogging may actually boost the immune system and reduce the risk of catching a cold or the flu. No one is quite sure why regular, moderate exercise improves immune function. The answer may lie in its effect on levels of stress hormones such as cortisol. Regular exercise appears to reduce cortisol, a hormone that lowers immunity when released in large amounts. It’s also been shown that immune cells responsible for attacking foreign invaders such as viruses and bacteria are increased with regular physical exercise.

In contrast to moderate activity, intense exercise appears to decrease immunity, particularly if it’s sustained. One study showed that athletes who did high intensity exercise for more than an hour-and-a-half in a single session showed decreased immunity for several days afterwards. Why would this be? The hormone cortisol may again be playing a role. With intense exercise, levels of cortisol, as well as other stress hormones appear to rise which can decrease immunity temporarily.

Does this mean intense exercise should be avoided? If training for a marathon or a triathlon, high intensity exercise may be required. The key is to have long periods of rest between intense exercise sessions, at least two days, to allow cortisol levels to return to normal and the body to recover. Eating a nutritious, moderate protein diet high in complex carbohydrates may also help to fuel the body and offset the decrease in immunity associated with intense exercise. It’s also important when training for a marathon to allow adequate rest time.

The bottom line? Moderate exercise seems to have the most benefits for the immune system. Studies suggest that it may actually decrease the overall risk of catching a cold or the flu. Thus, it may be best for overall health. If intense workouts are to be done, they should be followed by adequate rest to give the body time to completely recover from the stress of high intensity exercise.