Validity of a Cochrane Systematic Review and meta-analysis for determining the safety of vitamin E

Ref ID	245
First Author	C. J. Oliver
Journal	BMC COMPLEMENTARY & ALTERNATIVE MEDICINE
Year Of Publishing	2017
URL	https://bmccomplementmedtherapies.biomedcentral.com/track/pdf/10.1186/s12906-017-1906-x.pdf
Keywords	• Vitamins and supplements • External validity • Cochrane
Problem(s)	• Weaknesses identified in some Cochrane reviews • Overly stringent inclusion criteria affecting external validity • Inflexible methods to complex questions
Number of systematic reviews included	1
Summary of Findings	An analysis of one Cochrane Systematic Review published in 2012 which concluded that α-tocopherol forms of vitamin E found a 3 cell analytical method comparing all vitamin E cells (vitamin E alone plus vitamin E + β-carotene) to the placebo only cell. This meta-analysis had the unfortunate effect of incorrectly inflating the mortality risk attributed to vitamin E by not balancing the contribution to mortality of the β-carotene intervention. Studies with low numbers of events, i.e. low mortality rates, had little or no impact on the analysis and resulted in a high weighting on the ABTC study from A11. Re-analysis of the ATBC trial using data derived from the more generally accepted ‘inside the table’ (2 cell – vitamin E versus placebo) or ‘at the margins’ (4 cell – all vitamin E versus all non-vitamin E) analytical methods demonstrates a statistically non-significant result. The authors state that current meta-analysis methods do not allow for studies with low (or no) mortality to be incorporated in a meaningful way.
Did the article find that the problem(s) led to qualitative changes in interpretation of the results?	Yes
Are the methods of the article described in enough detail to replicate the study?	Yes