Vitamin C supplementation for asthma.

BACKGROUND Vitamin C is one of the key antioxidant vitamins which is abundant in the extracellular fluid lining the lung and low vitamin C intake has been associated with pulmonary dysfunction. OBJECTIVES To evaluate the evidence for the efficacy of vitamin C in the treatment of asthma. SEARCH STRATEGY The Cochrane Airways Review Group asthma register was searched and bibliographies of studies identified were also checked for further trials. This review has been updated by searches to January 2004. SELECTION CRITERIA Only randomised controlled trials were eligible for inclusion. Studies were considered for inclusion if they dealt with the treatment of asthma using vitamin C supplementation. Two independent reviewers identified potentially relevant studies using pre-defined criteria and selected studies for inclusion. DATA COLLECTION AND ANALYSIS Data were abstracted independently by two reviewers. Information on patients, methods, interventions, outcomes and results was extracted using standard forms. MAIN RESULTS A total of 71 abstracts and titles were identified. Sixteen studies were selected for potential inclusion, eight met the inclusion criteria. All included studies were placebo-controlled and randomised. Only four provided data in a form that permitted further analysis and none could be aggregated in a meta analysis. The individual studies did not show a significant effect on any asthma outcome. The 2004 update for this review includes a large study in 201 adults on inhaled corticosteroids in which important benefit from the addition of vitamin C was excluded by the narrow confidence intervals of the lung function results. REVIEWERS' CONCLUSIONS 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 warranted in order to address the question of the effectiveness of vitamin C in children with asthma.