Cochrane Summaries

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Vitamin C for asthma and exercise-induced breathlessness

Milan SJ, Hart A, Wilkinson M
Published Online: 
23 October 2013

Review question

This review considered the question of whether vitamin C may be helpful for people with asthma or exercise-induced breathlessness.

Background

Asthma is an inflammatory lung condition characterised by the narrowing of airways and is associated with wheezing, breathlessness, cough and chest tightness. Vitamin C has been suggested as a possible treatment for asthma.

Study characteristics

Eleven studies on 419 people with asthma or exercise-induced breathlessness were included in this review comparing vitamin C compared to placebo (no vitamin C). Most studies were in adults and one small study was in children. The small number of studies available for review and their different designs meant that we were only able to describe individual studies, rather than pooling the results together to get an average from the trials. The study design was not well described in most study reports and therefore it was impossible to determine risk of bias for most of the studies. There was very little data available in the trials for our key outcomes and this may indicate some selective outcome reporting.

Key results

There was no indication of benefit from the studies that considered vitamin C in relation to asthma. However, it is not possible to form any clear conclusions on the basis of those studies at this stage. The review concludes that there is insufficient evidence currently available to evaluate the use of vitamin C as a treatment in asthma. Larger, well-designed research is needed to provide clearer guidance. There was some indication that vitamin C was helpful in exercise-induced breathlessness in terms of how easily people breathe and their symptoms; however, as these findings were provided by only very small studies they do not provide complete answers to guide treatment.

Quality of the evidence

Details of the way patients were allocated to receive vitamin C or not were not clearly described in 10 of the 11 studies and we considered this carefully in the review in relation to our level of uncertainty in interpreting the results. Taking this into account, together with the imprecision of the results, we judged the estimates of the usefulness of vitamin C as a treatment to be of either low or moderate quality in relation to asthma.

Additionally, for exercise-induced breathlessness the three studies providing data to the review were small and we are mindful of the need to draw very cautious conclusions about the results.

This plain language summary is current as of December 2012.

This record should be cited as: 
Milan SJ, Hart A, Wilkinson M. Vitamin C for asthma and exercise-induced bronchoconstriction. Cochrane Database of Systematic Reviews 2013, Issue 10. Art. No.: CD010391. DOI: 10.1002/14651858.CD010391.pub2
Assessed as up to date: 
19 December 2012