New Paradigm of Evidence-Based Nutrition

Continued from Yesterday

Prevention Vs. Treatment - Continued

The case of beta-carotene is an excellent example of inappropriate application of a therapeutic study design to address a prevention question. Decades ago, observational studies suggested that diets and/or serum high in beta-carotene were associated with a lower risk of certain cancers, including lung cancer. This lead to RCTs published in the mid-1990s (the famous “Finnish trials”19,20) in which lifelong smokers or asbestos workers were supplemented with high doses of antioxidants, such as beta-carotene. The results at the time were shocking: compared to placebo, supplementation with beta-carotene significantly increased the risk of lung cancer in these smokers and asbestos workers. To this day, some people misuse this example is misused to demonstrate that the results of a RCT invalidated earlier epidemiological data. Some clinicians guided by EBM conclude that beta-carotene presents a similar risk of increased lung cancer to all patients, including those who do not smoke or have asbestos exposure, and discontinued its use altogether. Indeed, in its evidence-based review system guidance document, FDA touts this example as one that justifies the EBM approach to data evaluation, stating that the results of RCTs “trump” those of observational studies.3 Ignored is the fact that the RCTs in smokers and asbestos workers asked and answered questions different from those of the earlier epidemiological studies. Assessing the effect of lifelong exposure to a modest amount of a nutrient in the context of the whole diet in a general population that is healthy at baseline is completely different from administering a high dose of a single, purified, and isolated nutrient to a very specific population (eg, lifelong smokers) that is not healthy at baseline (because lung cancer was likely well on its way). In the latter case, beta-carotene was studied as a therapeutic drug, not a nutrient. Asking the question of whether beta-carotene can behave like a drug is certainly worthwhile, sometimes necessary. But the design and interpretation of such a study should be vastly different from one that studies a nutritive effect.

A quote from a recent editorial on nutrition and cancer summarizes the well intended, but misguided, beta-carotene trials: “By analogy, when keys are missing, it is common to look for them under the lamppost where there is light rather than in the murky location where the keys were more likely dropped.”21

Continued Tomorrow

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

http://www.depsyl.com/

http://back2basicnutrition.com/

http://bionutritionalresearch.olhblogspace.com/