Exercise, as it relates to your immune system, can be good and bad. Regular, moderate-intensity exercise can help to protect you against some diseases (especially those that involve the upper respiratory tract, like colds). However, overdoing it can have the opposite effect and reduce immunity. You’ve got to know how much exercise is enough; when you should exercise and when you should not; and which types of exercise are appropriate for your physical condition.
How does exercise boost immunity?
Exercise has been shown to increase the production of certain cells (macrophages) that attack the kinds of bacteria that can trigger upper-respiratory diseases. Cells that promote immunity circulate through the system more rapidly, and they’re capable of killing both viruses and bacteria. After exercising, the body returns to normal within a few hours, but regular exercise appears to extend periods of immunity.
It is also believed that the temporary rise in body temperature that occurs during exercise may inhibit the growth of bacteria. This process allows the body to fight infection more effectively. Exercise also slows the release of stress-related hormones, which can increase the likelihood of illnesses.
However, too much exercise appears to negatively affect immunity. One study found that 90 minutes or more of high-intensity exercise (marathons, endurance races, etc.) makes a person more susceptible to illness for up to 72 hours after working out. During exercise, the body produces two hormones — cortisol and adrenaline — that raise blood pressure, elevate cholesterol levels, and temporarily weaken the immune system.
Heavy, long-term exercise could increase the amount of white blood cells and increase the presence of stress-related hormones. Marathon and triathlon athletes are particularly vulnerable to increased susceptibility to infection, although susceptibility doesn’t automatically lead to infection.
Should you exercise when you’re sick?
It’s typically safe to exercise at a low intensity if you have “above-the-neck” symptoms (runny nose, sneezing, sore throat). If those symptoms diminish during the first few minutes of exercise, it’s safe to increase your exercise intensity level. Exercise is not recommended if you have “below-the-neck” symptoms (fever, sore muscles or joints, vomiting, diarrhea, or a cough that produces mucous). If you have those symptoms, it’s better to let the cold run its course before you resume physical activity.
What else can you do to stay healthy?
- Minimize stress
- Eat well (vitamins and minerals)
- Get enough rest, sleep
- Maintain reasonable weight
- Wash hands frequently
- Avoid sick people
- Get a flu shot
Regular, moderate-intensity exercise (about 30+ minutes per day) can help your body resist a variety of diseases. High-intensity endurance activities that last 90 minutes or more may increase your susceptibility to infection for up to three days. As with diet and other health-related behaviors, an exercise program that consistently and progressively challenges your body, without overdoing it, is the most sensible training strategy.
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