Should you not exercise when you have a cold? Or will exercise actually help keep you healthy by boosting your immunity?
One theory is that moderate aerobic exercise improves immunity and protects you from colds and other infections, whereas prolonged and/or very intense exercise (such as training for a marathon) can depress the immune system, elevate systemic inflammation, and increase the risk of colds.
But research doesn’t completely back up these ideas. The effect of exercise on immunity is not easy to study. Age, fitness level, and type and duration of workouts can all affect immunity.
Moreover, the human immune system is very complex. Researchers have to settle for the measurement of just one or a few components of immunity—usually a type of immune cell or protein—and the changes detected are not long-lasting. There isn’t a single test or marker of immune function that can predict whether exercise affects your susceptibility to infection or immunity-related diseases.
Athletes vs. the rest of us
Olympians and other highly trained athletes often report that after intense training and competition, they are more susceptible to colds. High-intensity or prolonged exercise does step up the output of two so-called stress hormones, cortisol and adrenaline, both of which can depress various elements of the immune system.
But while some studies show that people who run at least 20 miles, for instance, or 40 miles a week are more likely to develop a cold (or other upper respiratory infection) than those who run less than 10 miles, other studies have found that people in intensive training don’t get more colds.
There’s also debate about whether, or how much, moderate exercise boosts immunity. Some research has shown that sedentary people don’t have as vigorous an immune system as those who exercise, and that moderate exercise improves aspects of immunity. But no one knows if this leads to any real-world protective effect.
Bottom line: When you put on your exercise clothes, don’t worry about your immune system. Most people get too little exercise rather than too much, and the risks of being sedentary far outweigh the risks of catching a cold after exercising too much. In addition, most of us simply feel better when we exercise than when we lead a sedentary life.
If you have a mild cold, you can continue to exercise. If you feel flu-ish (muscle aches, fever, a cough, sore throat), rest until the symptoms pass.