Vitamin C supplementation for asthma

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.

To evaluate the evidence for the effectiveness of vitamin C in the treatment of asthma.

The Cochrane Airways Review Group asthma register was searched and bibliographies of studies identified were also checked for further trials.

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 were abstracted independently by two reviewers. Information on patients, methods, interventions, outcomes and results was extracted using standard forms.

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.

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.