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 August 2008.
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: Nine studies met the review entry criteria, randomising a total of 330 participants. Study design varied and the reporting was generally poor. Five trials contributed numerical data to the review. They provided outcome data on lung function, symptom scores, IgE levels and inhaled steroid use. One small study showed a significant difference in % drop in FEV1 post-exercise.
Authors' 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 needed in order to address the question of the effectiveness of vitamin C in children with asthma.