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Exercise and the Immune System

- Dr. James Meschino, DC, MS, ROHP


Moderate exercise (run 20-30 km per wk) increases immune function, but intensive training can weaken immune function. (1) After 3 hrs of endurance training:

  1. Epinephrine and cortisol levels 59% above baseline (catabolism).
  2. This weakens immune system (high cortisone levels).
  3. 25-46% decline in natural killer cells (NKC) at1.5-6 hrs post ex.
  4. NKC responsible for 10-15% of all lymphocytes (1st line defense against viral infections).
  5. NKC also destroy cancer cells and mutated cells.
  6. Increased WBC count (leukocytosis) lasting for 21 hrs post ex, likely due to inflammation and elevated cortisol levels.
  7. Marathon runners show higher incidence of URT post-race than non competitors. Vitamin C at 600 mg per day shown to reduce URT in this group. (Also glutamine supplementation) (2- 11)

Study By Peters et al (1993 –Am J Clin Nutr):

14 days after a 90 km road race on foot, the vitamin C group (600 mg per day during training and after) showed 33% incidence of URT infections vs 68% in the placebo group, who’s symptoms were more severe and lasted longer.

A 21 km run produced a 20% decline in plasma Vitamin C, (on average) with increased Vitamin C excretion in urine and sweat.

Vitamin C used to quench oxygen free radicals generated during aerobic metabolism, hence its requirement increases (12-14).

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Exercise and

the Immune System

Dr. James Meschino, 



1. Shephard RJ, Shek PN. Exercise, immunity, and susceptibility to infection: a J-shaped relationship? Physician Sportsmed 1999; 27(6): 47-48.
2. Nieman DC. Exercise infection and immunity. Int J Sports Med 1994; 15: S131-141.
3. Shephard RJ, Shek PN. Effects of exercise and training on natural killer cell counts and cytolytic activity: a meta-analysis. Sports Med 1999; 28(3): 177-95.
4. Shek PN, Sabiston BH, Buguet A, Radomski MW. Strenuous exercise and immunological changes: a multiple-time-point analysis of leukocyte subsets, CD4/CD8 ratio, immunoglobulin production and NK cell response. Int J Sports Med 1995; 16(7): 466-474.
5. Pederson BK, Tvede N, Hansen FR, Andersen V, Bendix T, Bendixen G. Modulation of natural killer cell activity in peripheral blood by physical exercise. Scand J Immunol 1988; 27(6): 673-678.
6. Woods JA, Davis JM, Mayer EP, Ghaffar A, Pate RR. Effects of exercise on macrophage activation for antitumor cytotoxicity. J Appl Physiol 1994; 76(5): 2177-2185.
7. Verde TJ, Thomas SG, Moore RW, Shek P, Shephard RJ. Immune responses and increasing training of the athlete. J Appl Physiol 1992; 73(4): 1494-1499.
8. Lotzerich H, Wilczkowiak I, Stein N. Influence of training and competition on the phagocyte activity of athletes. Int J Sports Med 1997; 18(suppl 1): S111 [abstract].
9. Mackinnon LT. Immunity in athletes. Int J Sports Med 1997; 18(suppl 1): S62-68.
10. Mackinnon LT. Exercise and Immunology. Champaign IL: Human Kinetics; 1992.
11. Mackinnon LT. Exercise and immunoglobulins. Exerc Immunol Rev 1996; 2: 1-34.
12. Peters-Futre EM. Vitamin C, neutrophil function and upper respiratory tract infection risk in distance runners: the missing link? Exerc Immunol Rev 1997; 3: 32-52.
13. Peters EM, Bateman ED. Ultramarathon running and upper respiratory tract infections: an epidemiological survey. S Afr Med J 1983; 64(15): 582-584.
14. Peters EM. Exercise, immunology and upper respiratory tract infections. Int J Sports Med 1997; 18(suppl 1): S69-77.

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