Oral magnesium and vitamin C supplements in asthma: a parallel group randomized placebo-controlled trial. Blocking effect of vitamin C in exercise-induced asthma. The effect of vitamin C on antigen-induced bronchospasm. A randomized controlled trial of vitamin C in the prevention and amelioration of the common cold. A prospective study of diet and adult-onset asthma. The clinical effects of vitamin C supplementation in elderly hospitalised patients with acute respiratory infections. Winter illness and vitamin C: the effect of relatively low doses. High dose ascorbic acid in Nigerian asthmatics.
Epidemiological studies suggest that higher intakes of dietary vitamin C and magnesium may be associated with a reduced risk of asthma.
                To determine whether vitamin C or magnesium supplements improve the clinical control of asthma in primary care patients.
                A randomized, placebo-controlled, double-blind parallel group trial of 16 weeks supplementation with 1 g/day vitamin C, 450 mg/day magnesium chelate or matched placebo. Three hundred patients aged 18-60 years with physician-diagnosed asthma, controlled with at least one dose of an inhaled corticosteroid daily, were recruited from 24 primary care practices in Nottingham, UK. The main outcome measures were change in forced expiratory volume in 1 s, forced vital capacity, airway responsiveness to methacholine, mean morning and evening peak flow, symptom scores and bronchodilator use, both individually and as a combined summary statistic.
                There was no evidence of any beneficial effect of either supplement on any outcome measure of asthma control in the primary intention-to-treat analysis, or in an analysis restricted to participants who completed the study.
                Regular dietary supplementation with vitamin C or magnesium adds no clinical benefit to current standard therapy of asthma in primary care patients. To determine if vitamin C (ascorbic acid) has a protective effect on the hyperreactive airways of patients with exercise-induced asthma (EIA).
                All the patients underwent pulmonary function tests at rest, before and 1 hour after receiving 2 g of oral ascorbic acid. They were then randomly assigned in a double-blind manner to receive 2 g of ascorbic acid or a placebo 1 hour before a 7-minute exercise session on a treadmill. Pulmonary function tests were performed after an 8-minute rest. This procedure was repeated 1 week later, with each patient receiving the alternative medication.
                A university hospital.
                Twenty patients with asthma (13 males and 7 females), with ages ranging from 7 to 28 years (mean, 13.8 years). All patients who had a decline of at least 15% in their forced expiratory volume in 1 second after a standard exercise test on a motorized treadmill received a diagnosis of EIA. MAIN-OUTCOME MEASURES: All patients were advised to stop using their regular asthma medication or bronchodilator 12 hours before the test. Pulmonary function tests were performed in the same ambient conditions on all patients.
                All patients received a diagnosis of EIA. Ascorbic acid administration did not change the results of pulmonary functions at rest after 1 hour. In 9 patients, a protective effect on exercise-induced hyperreactive airways was documented. Four of 5 patients who received ascorbic acid and documented a protective effect on EIA continued to receive ascorbic acid, 0.5 g/d, for 2 more weeks with the same protective effect.
                The efficacy of vitamin C in preventing EIA cannot be predicted. However, vitamin C may have a protective effect on airway hyperreactivity in some patients with EIA. The effect of vitamin C pretreatment in preventing ragweed-induced bronchospasm was evaluated in 6 ragweed-sensitive asthmatics studied in a double-blind randomized fashion. The patients received either lactose capsules or 500 mg of ascorbic acid and were studied out of season. Antigen dose-response curves were determined prior to the administration of lactose or ascorbic acid in each individual subject and subsequently after administration of ascorbic acid or lactose. Bothe PD20FEV1 (provocation dose necessary for a 20% reduction in forced expiratory volume in 1 second) and PD35SGaw (provocation dose necessary for a 35% reduction in specific airways conductance) were determined. In none of the six patients was there a change in baseline FEV 1 (p greater than 0.70) nor the overall average baseline specific airways conductance (rho greater than 0.90). Additionally, no statistically significant difference (p greater than 0.60) was noted between log PD35SGaw vitamin C day and lactose day. Likewise, no statistically significant difference (p greater than 0.60) was evident when comparing log PD20FEV1 lactose and ascorbic acid days. Vitamin C (500 MG) HAS NO PROTECTIVE EFFECT AGAINST RAGWEED ANTIGEN-INDUCED BRONCHOSPASM. A randomized controlled trial of the effect of 1 g ascorbic acid per day in the prevention of the common cold was conducted on 688 adult women. There is evidence of a small reduction by vitamin C in the mean number of chest colds, but no evidence of any effect on simple colds. The existence of a subgroup of vulnerable women in the community who benefit from vitamin C was considered but further examination of the data gives no support to this conclusion. A role for diet in the pathophysiology of asthma may be mediated by altered immune or antioxidant activity with consequent effects on airway inflammation. We evaluated associations between several dietary factors assessed by a semiquantitative food frequency questionnaire, and incidence of asthma over a 10-yr period in 77,866 women 34 to 68 yr of age. Women in the highest quintile of vitamin E intake from diet, but not from supplements, had a risk of 0.53 (95% confidence interval [CI] = 0.33 to 0.86) compared with women in the lowest quintile. This relationship, however, was attenuated when the contribution from nuts, a major source of vitamin E in these data and a possible allergen, was removed (relative risk = 0.74 [0.50 to 1.10], p for trend = 0.007). Positive associations were found for vitamins C and E from supplements, but appeared to be explained by women at high risk of asthma initiating use of vitamin supplements prior to diagnosis. A nonsignificant inverse association with carotene intake was noted, but no clear relations with asthma were demonstrated for intake of linoleic acid or omega-3 fatty acids. These data suggest that antioxidant supplementation and intake of various fats during adulthood are not important determinants of asthma, although vitamin E from diet may have a modest protective effect. A randomised double-blind trial involving vitamin C/placebo supplementation was conducted on 57 elderly patients admitted to hospital with acute respiratory infections (bronchitis and bronchopneumonia). Patients were assessed clinically and biochemically on admission and again at 2 and 4 weeks after admission having received either 200 mg vitamin C per day, or placebo. This relatively modest oral dose led to a significant increase in plasma and white cell vitamin C concentration even in the presence of acute respiratory infection. Using a clinical scoring system based on major symptoms of the respiratory condition, patients supplemented with the vitamin fared significantly better than those on placebo. This was particularly the case for those commencing the trial most severely ill, many of whom had very low plasma and white cell vitamin C concentrations on admission. Various mechanisms by which vitamin C could assist this type of patient are discussed. After their random -llocation to one of three treatment aroups, 622 volunteers received either vitamin C or placebo in a maintenance dose of 500 mg once weekly and a therapeutic dose of 1500 mg daily on the 1st day and 1000 mg on the next 4 days of any illness. Two forms of vitamin C were employed: a sustained-release capsule containing ascorbic acid and a regular tabet containing a mixture of sodium and calcium ascorbate. In the 448 subjects who completed an average of 15 weeks in the study of total of 635 episodes of illness were recroded. Respiratory symptoms were recorded on at least 1 day in 92 per cent of these episodes. There were no consistent or significant differences in the sickness experience of the subjects receiving the sustained-release vitamin capsules compared to those receiving the vitamin tablets, but subjects in both vitamin groups experienced less severe illness than subjects in the placebo group, with approximately 25 per cent fewer days spent indoors because of the illness (P smaller than 0.05). These results are compatible with the belief that supplementary vitamin C can reduce the burden of winter illness, but the intake need not be as high as has sometimes been claimed. Forty-one asthmatic patients in remission were randomly allocated to two treatment groups in a double-blind trial. One group took 1 g, of ascorbic acid as one effervescent tablet once daily and the second group took a matching placebo. The asthmatics were selected from those attending the Asthma Clinic. One criterion for selection was the increase in exacerbation during the rainy season. These exacerbations were precipitated by respiratory infection. After 14 weeks, an assessment of the severity and rate of attacks showed that those on ascorbic acid suffered less severe and less frequent attacks of asthma during the study period. Plasma ascorbic acid astimations showed a significant rise in the level in those taking ascorbic acid over those on placebo. (P < 0.01). Cessation of ascorbic acid in the group taking it increased attack rates. It is concluded that high dose ascorbic acid is probably a good prophylaxis in some bronchial asthmatics.
At present, evidence from randomised-controlled trials is insufficient to recommend a specific role for vitamin C in the treatment of asthma. Further methodologically strong and large-scale randomised controlled trials are needed in order to address the question of the effectiveness of vitamin C in asthma.