New Paradigm of Evidence-Based Nutrition

Continued from Yesterday:

Despite this assertion, regard for the principles of EBM and the RCT as the unquestioned gold standard have resulted in the misuse of the WHI trial as part of the evidence base supporting calcium and vitamin Ds effect on fracture risk.Despite this assertion, regard for the principles of EBM and the RCT as the unquestioned gold standard have resulted in the misuse of the WHI trial as part of the evidence base supporting calcium and vitamin D’s effect on fracture risk. In a recent meta-analysis,16 the WHI study, as a large RCT, was automatically assigned the most weight by far among the 17 studies included in the analysis. This resulted in a skewed effect on fracture risk toward the null (although the combined effects of the other, smaller trials included in the analysis still resulted in a statistically significant 17 combined 12% reduction in fracture risk). Systematic reviews and meta-analyses should be interpreted judiciously and should not be considered on their own as high-level evidence because they are statistically assisted interpretations of primary evidence that carry their own set of limitations and biases.

The Selenium and Vitamin E Cancer Prevention Trial (SELECT)11 is an example of a high-profile RCT whose results have been largely misinterpreted and miscommunicated. The investigators terminated the study early, concluding there was no beneficial effect of selenium and vitamin E supplementation on prostate cancer risk. The form of selenium used in SELECT (selenomethionine) is different from the yeast-based selenium product used in a previous trial, which suggested through a secondary analysis that supplemental selenium could lower the risk of prostate cancer.16 The decision to utilize an alternate form of selenium was apparently driven by the need to use standardized and highly stable material that would maintain consistency throughout the length of a multiyear trial. This could not be achieved with yeast-based selenium, hence the decision to use selenomethionine. This is a common dilemma encountered by nutrition researchers investigating bioactive compounds derived from natural sources, such as fish oil, bovine colostrum, and probiotics, and yet illustrates another way the traditional RCT model does not account for the subtle nuances of nutrition interventions. Furthermore, the subjects enrolled in the study by Clark et al had relatively low baseline serum selenium levels (suggesting they were inadequate or insufficient), whereas the majority of men enrolled in SELECT were relatively replete in selenium. Finally, the men enrolled in SELECT had extremely low risk for prostate cancer—only 1 death due to prostate cancer occurred in the entire cohort, making it more difficult to detect an effect of the intervention. These seemingly minor limitations may have had a major impact on the outcome, an issue that has been inadequately communicated to practitioners and the public.

Continued Tomorrow

http://www.naturalmedicinejournal.com/article_content.asp?article=117

http://www.depsyl.com/

http://back2basicnutrition.com/

http://bionutritionalresearch.olhblogspace.com/