Vitamin C and asthma

by Harri Hemilä

Department of Public Health
University of Helsinki, Finland
harri.hemila@helsinki.fi
https://www.mv.helsinki.fi/home/hemila
Feb 4, 2025

Original articles and systematic reviews
Flaws in the Cochrane review on "vitamin C supplementation and asthma" (published in 2001 and withdrawn in 2013). The review had severe errors in extraction of data and in data analysis and misled readers for a decade.
Letters and commentaries

Original articles and systematic reviews

Review on vitamin C and EIB, and a secondary analysis of a published study
Hemila H
The effect of vitamin C on bronchoconstriction and respiratory symptoms caused by exercise: a review and statistical analysis.
Allergy, Asthma & Clinical Immunology 2014;10:58
https://doi.org/10.1186/1710-1492-10-58
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4363347

Three studies found that vitamin C decreased common cold induced asthma exacerbations or bronchial hypersensitivity.
Hemila H
Vitamin C and common cold-induced asthma: a systematic review and statistical analysis.
Allergy, Asthma Clin Immunol 2013;9:46
https://doi.org/10.1186/1710-1492-9-46
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4018579

Three studies found that vitamin C halved the FEV1 decline caused by exercise.
Hemila H
Vitamin C may alleviate exercise-induced bronchoconstriction: a meta-analysis.
BMJ Open 2013;3:e002416
https://doi.org/10.1136/bmjopen-2012-002416
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3686214

Vitamin C was reported to alleviate asthma severity in Egyptian children, but the data set was found to be flawed.
Still the Egyptian study indicates that the effect of vitamin C should be further studied,
even though the validity of these particular findings is not clear.
Hemila H, Al-Biltagi M, Basset AA
Vitamin C and asthma in children: modification of the effect by age, exposure to dampness and the severity of asthma.
Clin Transl Allergy 2011;1:9
https://doi.org/10.1186/2045-7022-1-9
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3339402
Retraction:
https://doi.org/10.1186/2045-7022-2-6
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3320558
https://www.ncbi.nlm.nih.gov/pubmed/22423606
Postpublication problems: reasons for the retraction:
https://www.mv.helsinki.fi/home/hemila/PPH/CTA/CTA.html
See also retraction of the initial publication on which the above 2011 subgroup analysis was based:
https://doi.org/10.1111/j.1651-2227.2012.02723.x

Flaws in the Cochrane review on ”vitamin C supplementation and asthma"”
(published in 2001 and withdrawn in 2013).

The Cochrane review had severe errors in the extraction of data and in data analysis and misled readers for a decade.

Meta-analysis of 3 exercise-induced asthma trials and pointing out errors in the Cochrane review
This was expanded to BMJ Open paper in 2013, see above

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Pointing out errors in the Cochrane review and a meta-analysis of 3 exercise-induced asthma trials
The meta-analysis was expanded to BMJ Open paper in 2013
The Cochrane review on vitamin C and asthma misled readers for a decade from 2001 to 2013
Hemilä H. Feedback [on the Cochrane review “vitamin C supplementation for asthma” (2009) by Kaur B, Rowe BH, Stovold E]
Cochrane Database of Systematic Reviews CD000993 [Feedback 24 March 2009]
https://helda.helsinki.fi/handle/10138/38500
https://doi.org/10.13140/2.1.1280.3364
    The above comment was submitted in 2009, but the authors replied no earlier than in 2012.
    Furthermore, the reply was full of errors:
    Hemilä H
    Vitamin C and exercise-induced bronchoconstriction:
    further problems in the Cochrane review "vitamin C for asthma" (2013).
    Unpublished commentary
    https://hdl.handle.net/10138/40816

The Cochrane review on vitamin C and asthma misled readers for a decade from 2001 to 2013.
See the PubMed records of the Cohrane review on vitamin C and asthma from 2001 to 2013:
https://pubmed.ncbi.nlm.nih.gov/11687089/   2001
https://doi.org/10.1002/14651858.CD000993

https://pubmed.ncbi.nlm.nih.gov/15266435/   2004
https://doi.org/10.1002/14651858.CD000993.pub2

https://pubmed.ncbi.nlm.nih.gov/19160185/ 2009
https://doi.org/10.1002/14651858.CD000993.pub3

https://pubmed.ncbi.nlm.nih.gov/24155047/   2013 Withdrawal of the Cochrane review
https://doi.org/10.1002/14651858.CD000993.pub4
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Letters and commentaries

Hemilä H. Evidence-based management of EIB with vitamin C
BMJ eLetter 29 Feb 2016
https://www.bmj.com/content/352/bmj.h6951/rr

Hemila H. Vitamin C and asthma.
JACI 2014;134:1216
https://doi.org/10.1016/j.jaci.2014.08.032