The review question was clear with broadly defined inclusion criteria. A limited search was conducted so potentially relevant data may have been missed. Study quality did not appear to be assessed so it was difficult to assess the reliability of the evidence. The author did not report whether appropriate methods to reduce reviewer error and bias (such as independent reviewers conducting study selection and data extraction) were used throughout the review process.
A narrative synthesis was appropriate given the differences between studies in terms of design, outcomes and outcome measurement. Reporting of study characteristics was limited and it was difficult to assess the generalisability of the results. Use of self-reported data and observational studies were potential limitations. Details of the two negative studies were not discussed.
The author’s conclusion reflects the evidence presented but poor reporting of review methods, lack of quality assessment and reporting of study details, and the limited evidence base question the reliability of the conclusions.