I have several chronic illnesses only partially addressed by accepted pharmaceuticals,
so I am always interested in hearing that this or that vitamin or supplement is useful. Many autoimmune disorders and depression are associated with and/or exasperated by vitamin deficiencies. I always go to a reputable site like NIH or Mayo clinic or WEB MD to check my info. I don't trust the claims of someone who just happens to be selling the stuff. But I am very frustrated by the type of study I see all too often:
"Many patients with X suffer from a deficiency of Y. It has been reported that by supplementing Y, patients with X improved.
We gave 50 patients with X so many mgs of Y for 50 days and another 50 patients a placebo.
At the end of the test, supplementation with Y did not show a difference compared with the placebo.
Therefore, we conclude that Y does not improve the condition of patients with X."
Now - do you see what is missing from the model? Although many patients with X have a deficiency of Y, we have no idea if the patients involved in this particular study had a deficiency of Y. No one measured their serum levels before the protocol began, no one measured serum levels at the end of the study. We have no idea if these people had normal levels or not, nor do we know whether the supplementation was sufficient to bring them into normal levels.
Vitamin D is now recognized as very important in preventing and/or modulating many chronic illnesses. But today the recommended dose is something like 2000IU. A lot of older testing was done with a dose of 400IU, and it was concluded that Vitamin D wasn't a factor. It was only when the dose was raised to bring blood serum up to a certain point that the effects of Vitamin D could be seen.