Along those lines, a rather convoluted prospective case-control analysis of the Health Professions Follow-Up Study was published in the Journal of the National Cancer Institute just yesterday concluding that the highest quartile (top 25%) of vitamin D was associated w/57% lower risk of deadly prostate cancer compared to lowest quartile (bottom 25%). Granted their conclusion was a bit more detailed than that. After all, when you compare 1,260 men w/prostate cancer to 1,331 controls over several years, it's tricky to run through all the statistics. And this study actually looked into genetics, too, specifically single-nucleotide polymorphisms which are beyond the testing available to you & me.
2,000 units daily. Now if I could only figure out a good scheme at the tables . . .