Effect on immune system

Effect on the immune system

Although there have been hundreds of studies on exercise and the immune system, there is little direct evidence on its connection to illness.

Epidemiological evidence suggests that moderate exercise has a beneficial effect on the human immune system while extreme exercise impairs it, an effect which is modeled in a J curve. Moderate exercise has been associated with a 29% decreased incidence of upper respiratory tract infections (URTI), but studies of marathon runners found that their prolonged high-intensity exercise was associated with an increased risk of an infection, although another study did not find the effect.

Immune cell functions are impaired following acute sessions of prolonged, high-intensity exercise, and some studies have found that athletes are at a higher risk for infections.

The immune systems of athletes and nonathletes are generally similar. Athletes may have slightly elevated natural killer cell count and cytolytic action, but these are unlikely to be clinically significant.


Vitamin C supplementation has been associated with lower URTIs in marathon runners.
Biomarkers of inflammation such as C-reactive protein, which are associated with chronic diseases, are reduced in active individuals relative to sedentary individuals, and the positive effects of exercise may be due to its anti-inflammatory effects.

The depression in the immune system following acute bouts of exercise may be one of the mechanisms for this anti-inflammatory effect