Related: a 9-year, n=25871 study looking at long-term health outcomes of blind Vitamin D/Omega 3/placebo supplementation just ended and will have results out this summer.
One question: blind or double blind? Does the distributor also not know which product is being given to the patient?
I look forward to the results!
From anecdotes, the correlation studies, and my personal experience, I believe the results will be positive. If the results show otherwise, I'll accept it and try to understand why I was wrong.
Moreover, even in cases with low Vitamin D, where medical professionals are unsure if treatment with Vitamin D would be beneficial at all (in this case: for osteoporosis prevention)[2].
Finally, recent randomised, double-blind clinical trial (n=5108) assessed if monthly administration of a high dosage (100.000 IU) of Vitamin D for more than a year would in any way prevent cardiovascular disease, and found no benefit in patients receiving treatment or placebo after a 3.3 year follow-up period[3]. Another study (n=2303, 4-year long, 2000 IU/d), testing the efficacy of Vitamin D to prevent cancer, actually suggests that low dose of Vitamin D is may increase cancer.[4]
Taken together, I hope that this helps illustrate how 'making a prediction' or 'expecting a certain result' is neither scientifically ethical, nor possible, given the controversial results in the literature so far.
[1] https://www.ncbi.nlm.nih.gov/pubmed/21395958
[2] http://www.nejm.org/doi/pdf/10.1056/NEJMcp1009570
[3] https://jamanetwork.com/journals/jamacardiology/article-abst...