Background: Previous research has shown that diet can modify the bronchoconstrictor response to exercise in asthmatic subjects.
Objective: Determine the effect of ascorbic acid supplementation on pulmonary function and several urinary markers of airway inflammation in asthmatic subjects with exercise-induced bronchoconstriction (EIB).
Methods: Eight asthmatic subjects with documented EIB participated in a randomized, placebo controlled double-blind crossover trial. Subjects entered the study on their usual diet and were placed on either 2 weeks of ascorbic acid supplementation (1500 mg/day) or placebo, followed by a 1-week washout period, before crossing over to the alternative diet. Pre- and post-exercise pulmonary function, asthma symptom scores, fraction of exhaled nitric oxide (FENO), and urinary leukotriene (LT) C4-E4 and 9alpha, 11beta-prostagladin (PG) F2] were assessed at the beginning of the trial (usual diet) and at the end of each treatment period.
Results: The ascorbic acid diet significantly reduced (p < 0.05) the maximum fall in post-exercise FEV1 (-6.4 +/- 2.4%) compared to usual (-14.3 +/- 1.6%) and placebo diet (-12.9 +/- 2.4%). Asthma symptoms scores significantly improved (p<0.05) on the ascorbic acid diet compared to the placebo and usual diet. Post-exercise FENO, LTC4-E4 and 9alpha, 11beta-PGF2 concentration was significantly lower (p<0.05) on the ascorbic acid diet compared to the placebo and usual diet.
Conclusion: Ascorbic acid supplementation provides a protective effect against exercise-induced airway narrowing in asthmatic subjects.