Nutritional modulation of exercise-induced immunodepression in athletes: a systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized and controlled trials
PubMed 17136044 · doi:10.1038/sj.ejcn.1602549
What was done
Systematic review and meta-analysis of randomized and/or controlled trials assessing nutritional supplements to minimize exercise-induced immunodepression in athletes. The primary outcome was the incidence of upper respiratory tract (URT) illness symptoms after exercise. Secondary outcomes included cortisol, cell counts, plasma cytokine concentration, cell proliferative response, oxidative burst, natural killer cell activity, and immunoglobulins. The review analyzed 45 studies comprising 1,603 subjects (20 on carbohydrates, 13 on vitamin C, 8 on glutamine, and 4 on other interventions).
What was found
Vitamin C supplementation reduced post-exercise URT infections compared to placebo, with a pooled rate ratio of 0.49 (95% CI: 0.34–0.71; 3 trials assessed URT prevention, with vitamin C effect supported by 2 trials). Carbohydrate supplementation attenuated exercise-induced increases in cortisol and neutrophils. Vitamin C attenuated the post-exercise decrease in lymphocytes. No other interventions showed significant or consistent effects on the examined outcomes.
Why it matters
Athletes frequently use supplements to counter post-exercise immune suppression, but evidence is limited. This synthesis indicates that while vitamin C may halve post-exercise respiratory infection risk, evidence fails to support other popular interventions such as glutamine for preventing exercise-induced immunodepression.
Limits
The overall methodological quality of most included trials was poor. Studies were heterogeneous regarding exercise protocols, athlete populations, settings, and measured outcomes. Only three trials evaluated clinical infection outcomes, and numerical data for secondary immune markers were not reported in the abstract.
Cited by
- contradicts Glutamine supplementation reduces the incidence of respiratory illness in endurance athletes.
- contradicts Studies show that high-dose glutamine supplementation (approximately 30 g) reduces the incidence of respiratory tract infections in endurance athletes.