Written by Neil Levin, CCN, DANLA. A critique of methods used in vitamin D research.
My opinion: Randomized controlled trials are of little utility unless all relevant variables to the subject matter and clinical endpoints are controlled, as the application of a standard suggests. However, many so-called “vitamin studies” are in fact secondary analyses of previously published work. Unfortunately, in most cases the original study was never intended, or designed, to look at vitamins as a primary endpoint and so failed to collect and monitor the essential variables relevant to that nutrient. This is often true even if the original work was a “gold standard” study; that designation really applies only to the primary substances and endpoints that were correctly controlled in the original study, but not to subsequent analyses of secondary data to which the same gold standard was not separately and completely applied. Perhaps we need to create a new “platinum standard” to ensure that the relevant variables for nutrients are correctly identified and properly controlled in a study… This all-too-common lack of understanding of the relevant variables for studying nutrients (which of course are quite different and more varied than drug research variables since drugs are novel substances) makes much published secondary research on nutrients meaningless and confusing, with questionable results that seem to defy common sense being overhyped in sometimes excessive and sensational media coverage. This sometimes holds true for primary research on nutrients like vitamins and minerals, in which the gold standard appears to be used but is not faithfully executed in terms of identifying and controlling all relevant variables. In the case of vitamin D, relevant variables in a competent study should include collecting histories serum levels at baseline and after, as well as identifying and carefully measuring all of the various sources of the nutrient available to the subjects including skin pigmentation and sun exposure, diet and food fortification, and supplementation. But the majority of clinical trials on vitamins do not include all of these relevant variables and are therefore of questionable validity; often raising questions but not able to provide real answers. However, the European Food Safety Agency, a conservative EU governmental organization similar to our FDA, has a Panel on Dietetic Products, Nutrition and Allergies that reviews proposed health claims and issues Scientific Opinions. The Panel has recognized several benefits of vitamin D beyond bone health. (I bolded the benefits for visual emphasis):
- “On the basis of the data presented, the Panel concludes that a cause and effect relationship has been established between the intake of vitamin D and a reduction in the risk of falling. In order to obtain the claimed effect, 800 I.U. (20 μg) of vitamin D from all sources should be consumed daily. The target population is men and women 60 years of age and older.” http://www.efsa.europa.eu/en/efsajournal/pub/2382.htm
- “The Panel concludes that a cause and effect relationship has been established between the dietary intake of vitamin D and contribution to the normal function of the immune system and healthy inflammatory response, and maintenance of normal muscle function.” http://www.efsa.europa.eu/en/efsajournal/pub/1468.htm
A good quality vitamin D study should have variables that are well controlled which includes: vitamin D levels at start and end of study, identification of all sources of vitamin D such as: sun exposure, diet, food fortification and supplementation.
Posted December 11, 2013.
