To date, we have much research on vitamin D, the majority being epidemiological studies (observations of populations/groups of people) and some mechanistic studies (vitamin D actions). These kinds of studies show that vitamin D deficiency may be a risk factor for widespread diseases and also that vitamin D and its metabolites have mechanisms to keep the body functioning properly and ward off diseases.
However, public policy makers have decided that this kind of proof is inadequate, and that we need to treat vitamin D like a new drug. The gold standard of proof of efficacy of a new drug is a randomized controlled trial (RCT). Such trials include randomization to one of several groups (so that everyone in the groups are similar to begin with), then the “blinding” of both the patients and the researchers. This means that neither the patients nor the researchers know if they are getting/giving vitamin D or a sugar pill (placebo).
If it is a serious disease being studied, an objective third party opens the code periodically to see if either the vitamin D is helpful or harmful, as it would be unethical to continue the trial if one of either conditions were occurring. Sometimes randomization is not possible, so then, it simply becomes a controlled trial. Researchers then either publish or present their results or do both. Our informal count to date is over 50 positive controlled trials of vitamin D.
Researchers do not always first publish their findings in journals. Researchers sometimes first announce their findings at professional meetings and then later submit them for publication. Like you, we have to depend on the media to get information about RCTs first announced at meetings. Not all health reporters recognize the importance of RCTs, so some go unpublicized.
However, one that missed oblivion was Dr Faud Baroody’s recent trial on allergic rhinitis. This University of Chicago researcher simply gave 4,000 IU/day to the treatment group and standard treatment to both groups and discovered vitamin D helps allergic rhinitis. You can read about it yourself, so I won’t repeat what Medscape already provided.
Such positive RCTs are becoming so numerous, so positive, so one-sided, that the pressure on the Food and Nutrition Board should already be mounting. However, unless forced by political means, I doubt they will meet again for ten years, no matter how many RCTs lay in the dust behind them.