Vitamin C supplementation for asthma: Feedback submitted by Harri Hemila, 24 March 2009

In 2009, I found that there were several errors in the Cochrane review “vitamin C supplementation for asthma” (2009) [1]. For example, there were errors in data extraction; one trial had 20 participants, but only 11 participants were included in the Cochrane analysis. There were errors in the calculations, and the unpaired t-test was used when the paired test should have been used. My feedback was published in the (2010) version of the “2009” review [2], on page 27.

The managing editor, Emma Welsh, wrote a response to my criticism in the (2012) version of the “2009” Cochrane review [3]. Simultaneously, the three analysis figures, which were the main focus of my critique, were removed from the review [4]. In their absence, however, my feedback though originally valid became irrelevant. Furthermore, the remaining figures were renumbered so that the figure numbers in my feedback indicated real but different figures; therefore, readers would consider that I was confused. Finally, many responses by Welsh did not seem valid [4]. I contacted David Tovey, Editor-in-Chief of Cochrane, but our correspondence did not lead to any constructive efforts to correct the problem. After a year, I contacted COPE which stated that the original (2009) version must be made available to readers; see a brief summary of the long process [5].

As a result of this process, one single PubMed record (#19160185) [6] links to two different versions of the same “2009” Cochrane review. The PubMedCentral version (2009) includes all the original figures, but not my feedback [1]. The Cochrane Library version (2012) includes my feedback, but does not include the three analysis figures to which my feedback focused [3]. This document is a copy of that (2012) review [3]. My feedback is on pages 20-21.

Finally, a third version of the “vitamin C supplementation for asthma” (2010) has both the original figures and my feedback, and is available at the University of Helsinki Digital Archive and Zenodo [2]. Furthermore, the errors that I pointed out in 2009 existed already in the 2001 version of the Cochrane review, so the review had been misleading readers over a decade [4]. Eventually, the review was withdrawn by Cochrane [7].

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6176494

2. https://zenodo.org/doi/10.5281/zenodo.10853677

3. https://doi.org/10.1002/14651858.CD000993.pub3

4. https://zenodo.org/doi/10.5281/zenodo.6405803

5. https://doi.org/10.1111/eci.13216

6. https://pubmed.ncbi.nlm.nih.gov/19160185

7. https://pubmed.ncbi.nlm.nih.gov/24155047