This review was published as a brief communication and much of the detail of the methods was not reported. The inclusion criteria were clearly stated in terms of participants, treatment and outcome, but were less clear for study design. The search was limited to full text articles published in English and listed in one database or references. Therefore, it was possible that other relevant studies may have been missed and that language bias or publication bias could have affected the results of the review. The methods of study selection and data extraction were not described, so it was not possible to comment on their suitability for limiting the effects of possible error or reviewer bias.
There was no mention of any assessment of study quality, and there was little information about the included studies or their participants. This meant it was not possible to comment on either the validity of the data or the generalisability of results. The majority of the included studies were observational studies and, as the authors acknowledged, they are not considered to be as high quality as RCTs. It was possible that selection of participants for these studies may have been influenced by factors which may have had an influence on the results.
In view of this, along with the limited search and the lack of reporting of methods, the authors' conclusion should be treated with caution. However, they appear to partially acknowledge this by also stating that further research, using RCTs, is needed.