Exercise & the immune system
Exercise can have both a positive and negative impact on immune function, and striking the right balance can be a challenge for many fitness enthusiasts.
The relationship between exercise and immune function is best described as a J-shaped curve, where moderate activity may be beneficial, yet sedentary or excessive behaviour has the opposite effect.
So while regular exercise is thought to enhance immune function by stimulating a recirculation of cells from the immune system and decreasing the risk of infection, you can get too much of a good thing - prolonged high-intensity activity and high training volumes have been linked to reduce immune function, inflammation and oxidative stress.
How much should you exercise for a healthy immune system?
Upper respiratory tract infections (URTI) can be used as one measure of immune function.
The impact of exercise on your susceptibility to colds and sinusitis has been examined by a study
published the British Journal of Sports Medicine
It was found that high levels of physical fitness and near-daily cardiovascular activity reduced the frequency of URTI by just over 40% over a 12 week period. The severity of symptoms was also reduced by over 30%.
An additional study
on exercise and immune function published in the Journal of Applied Physiology
reviewed a number of scientific studies on the subject.
The author revealed that post-exercise immune function depression is most pronounced when the exercise is continuous, prolonged (longer than 1.5 hours), of higher intensity (55–75% of maximum capacity), and performed without food intake. It was also noted that periods of intensified training lasting a week or longer can result in longer lasting immune dysfunction (just like the J-Curve).
However, they also noted that people who are physically active on a regular basis experience a reduction in the levels of biomarkers that are used to assess systemic inflammation, a known marker of disease.