According to research, varying degrees of exercise can significantly decrease or increase the likelihood of getting a respiratory tract infection. Whilst regular moderate exercise helps to reduce the chance of getting cold-like infections, lengthy periods of strenuous exercise, like marathons, could make a person more susceptible.
Upper- respiratory tract infections are infections which have an effect on the throat, nose and sinuses, that include tonsillitis, the common cold, flu and sinusitis. Viruses which circulate in the environment typically bring about upper- respiratory tract infections. Although constantly confronted with these viruses, it’s the status of the immune system which determines if we succumb to infection or don’t. Exercise combined with genetics as well as other external factors such as poor nutrition, lack of sleep and stress, can have both a negative and positive effect on immune function. Together these factors determine a person’s susceptibility to infection.
Inactivity results in an average risk of getting 2-3 upper- respiratory tract infections annually. Studies have shown that people participating in regular moderate exercise, such as a brisk walk every day, could reduce the likelihood of getting a respiratory infection like a cold, by up to nearly one third. This benefit has been revealed to be the consequence of the cumulative effect of exercise resulting in long-term improvement in immunity.
On the other hand, after lengthy periods of strenuous exercise, the chance of a person becoming ill in fact increases. In the weeks after a marathon, research has revealed a 2 – 6 times increase in the chance of getting an upper respiratory infection. Endurance athletes are more susceptible to upper- respiratory tract infections due to their heavy training loads, and this is a problem for them as infections can mean competition under-performing or missing out on training sessions.
The main cells in the regulation of the immune system are immune cells known as Natural Killer cells that are important in fighting viral infections. Natural Killer cells identify viral-infected cells as foreign invaders and make them commit suicide. When exercising moderately, the activity of Natural Killer cells is increased, while stressful endurance activities like marathons can reduce Natural Killer cell activity. These changes are closely controlled by stress hormones along with other immune cells.