Effects of ascorbic acid deficiency on the in vitro biosynthesis of cyclooxygenase metabolites in guinea pig lungs

The effect of vitamin C on bronchoconstriction and respiratory symptoms caused by exercise: a review and statistical analysis

Physical activity increases oxidative stress and therefore the antioxidant effects of vitamin C administration might become evident in people undertaking vigorous exercise. Vitamin C is involved in the metabolism of histamine, prostaglandins, and cysteinyl leukotrienes, all of which appear to be mediators in the pathogenesis of exercise-induced bronchoconstriction (EIB). Three studies assessing the effect of vitamin C on patients with EIB were subjected to a meta-analysis and revealed that vitamin C reduced postexercise FEV1 decline by 48% (95% CI: 33% to 64%). The correlation between postexercise FEV1 decline and respiratory symptoms associated with exercise is poor, yet symptoms are the most relevant to patients. Five other studies examined subjects who were under short-term, heavy physical stress and revealed that vitamin C reduced the incidence of respiratory symptoms by 52% (95% CI: 36% to 65%). Another trial reported that vitamin C halved the duration of the respiratory symptoms in male adolescent competitive swimmers. Although FEV1 is the standard outcome for assessing EIB, other outcomes may provide additional information. In particular, the mean postexercise decline of FEF50 is twice the decline of FEV1. Schachter and Schlesinger (1982) reported the effect of vitamin C on exercise-induced FEF60 levels in 12 patients suffering from EIB and their data are analyzed in this paper. The postexercise FEF60 decline was greater than 60% for five participants and such a dramatic decline indicates that the absolute postexercise FEF60 level becomes an important outcome in its own right. Vitamin C increased postexercise FEF60 levels by 50% to 150% in those five participants, but had no significant effect in the other seven participants. Thus, future research on the effects of vitamin C on EIB should not be restricted to measuring only FEV1. Vitamin C is inexpensive and safe, and further study on those people who have EIB or respiratory symptoms associated with exercise is warranted.

Vitamin C may alleviate exercise-induced bronchoconstriction: a meta-analysis

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.

Vitamin C and asthma in children: modification of the effect by age, exposure to dampness and the severity of asthma

BACKGROUND

We previously found a significant benefit of vitamin C supplementation in asthmatic children.

PURPOSE

To test whether the effect of vitamin C on asthma is heterogeneous over the participant population.

METHODS

Egyptian asthmatic children between 7 and 10 years of age (n = 60) were included in the cross-over trial. They were administered 0.2 grams per day of vitamin C and placebo for separate 6-week periods. The variation in the vitamin C effect on two clinically relevant outcomes was analyzed: the childhood asthma control test (C-ACT), which measures the severity of asthma symptoms (the scale ranges from 0 to 27 points, < 20 points indicating unsatisfactory asthma control), and FEV1. We used linear modeling to examine the variation of the vitamin C effect in the subgroups.

RESULTS

The effect of vitamin C on the C-ACT was significantly modified by age and baseline C-ACT levels. In the children aged 7.0-8.2 years with a baseline C-ACT of 18 to 19 points, vitamin C increased the C-ACT score by 4.2 points (95% CI: 3.3-5.3); whereas in the children aged 8.3-10 years who had a baseline C-ACT of 14 to 15 points, vitamin C increased the C-ACT score by only 1.3 points (95% CI: 0.1-2.5). The effect of vitamin C on the FEV1 levels was significantly modified by age and exposure to dampness. In the children aged 7.0-8.2 years with no exposure to dampness, vitamin C increased the FEV1 level by 37% (95% CI: 34-40%), whereas in the children aged 8.3-10 years with exposure to dampness or mold in their bedroom more than one year prior to the study, vitamin C increased the FEV1 level by only 21% (95% CI: 18-25%).

CONCLUSIONS

We found strong evidence that the effect of vitamin C on asthmatic children is heterogeneous. Further research is needed to confirm our findings and identify the groups of children who would receive the greatest benefit from vitamin C supplementation.