Moderate Exercise Boosts the Body’s Defense (Immune) System

Regular sessions of moderate exercise has been linked to an improvement in the body’s defense (immune) system, which could protect individuals against infections of the throat and nose (commonly referred to as parts of the upper respiratory tract). 1 People who exercise regularly report fewer incidences of colds than those who lead sedentary lifestyles. Regular, consistent, moderate exercise can lead to substantial benefits in the immune system over the long term. Nevertheless, this benefit is not seen when people are doing intense exercise, as it may cause a temporary decrease in immune system function.

A long-term study in Columbia has demonstrated a 23% reduction in risk of upper respiratory tract infection in those engaging in regular physical activity compared to those who engage in irregular moderate-to-vigorous exercise.2 In addition, a recent study on the effect of exercise on the immune system of healthy older adults suggested that regular aerobic exercise appears to benefit the immune system by helping to balance the responses of the immune system and reducing the symptoms of inflammation.3

There are physiological changes in the immune system as a response to regular, moderate exercise. During moderate exercise, the immune cells circulate through the body more rapidly and have a better ability to kill the infecting pathogens (disease-causing bacteria or virus). Although the immune system returns to pre-exercise levels immediately after the exercise session, each session represents an expansion in the immune system surveillance, and this cumulative effect appears to reduce the risk of infection over the long-term.


  1. Jeurissen A, Bossuyt X, Ceuppens JL, Hespel P. The Effects of Physical Exercise on the Immune System. Ned Tijdschr Geneeskd. 2003; 147(28): 1347–1351. Article in Dutch.
  2. Matthews CE, Ockene IS, Freedson PS, Rosal MC, Herbert JR, et al. Physical Activity and Risk of Upper-respiratory Tract Infection. Med Sci Sports Exercise. 2000; 32: S292.
  3. Haaland DA, Sabljic TF, Baribeau DA, Mukovozov IM, Hart LE. Is Regular Exercise a Friend or Foe of the Aging Immune System? A Systematic Review. Clin J Sport Med. 2008; 18(6): 539–548.

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