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Vitamin C may alleviate exercise-induced bronchoconstriction: a meta-analysis
  1. Harri Hemilä
  1. Department of Public Health, University of Helsinki, Helsinki, Finland
  1. Correspondence to Dr Harri Hemilä; harri.hemila{at}helsinki.fi

Abstract

Objective To determine whether vitamin C administration influences exercise-induced bronchoconstriction (EIB).

Design Systematic review and meta-analysis.

Methods MEDLINE and Scopus were searched for placebo-controlled trials on vitamin C and EIB. The primary measures of vitamin C effect used in this study were: (1) the arithmetic difference and (2) the relative effect in the postexercise forced expiratory volume in 1 s (FEV1) decline between the vitamin C and placebo periods. The relative effect of vitamin C administration on FEV1 was analysed by using linear modelling for two studies that reported full or partial individual-level data. The arithmetic differences and the relative effects were pooled by the inverse variance method. A secondary measure of the vitamin C effect was the difference in the proportion of participants suffering from EIB on the vitamin C and placebo days.

Results 3 placebo-controlled trials that studied the effect of vitamin C on EIB were identified. In all, they had 40 participants. The pooled effect estimate indicated a reduction of 8.4 percentage points (95% CI 4.6 to 12) in the postexercise FEV1 decline when vitamin C was administered before exercise. The pooled relative effect estimate indicated a 48% reduction (95% CI 33% to 64%) in the postexercise FEV1 decline when vitamin C was administered before exercise. One study needed imputations to include it in the meta-analyses, but it also reported that vitamin C decreased the proportion of participants who suffered from EIB by 50 percentage points (95% CI 23 to 68); this comparison did not need data imputations.

Conclusions Given the safety and low cost of vitamin C, and the positive findings for vitamin C administration in the three EIB studies, it seems reasonable for physically active people to test vitamin C when they have respiratory symptoms such as cough associated with exercise. Further research on the effects of vitamin C on EIB is warranted.

  • Nutrition & Dietetics
  • Sports Medicine

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