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 effectiveness 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. 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 65 abstracts and titles were identified. Ten studies were selected for potential inclusion, six met the inclusion criteria. All included studies were placebo-controlled and randomised. Only three provided data in a form that permitted further analysis and none could be aggregated in a meta analysis. The individual studies produced no significant effect on any asthma outcome. REVIEWER'S
CONCLUSIONS: At present, evidence from randomised-controlled trials is insufficient to recommend a specific role for vitamin C in the treatment of asthma. A methodologically strong and large-scale randomised controlled trial is warranted in order to address the question of the effectiveness of vitamin C in patients with asthma.