I read the study that is cited on your link. It was a review article about Vitamin D, not a study on Vitamin D toxicity. And in fact, in the references for that article, there is no study cited directly related to Vitamin D toxicity that I can see. The cutoff at 10K is largely someone's opinion. I cannot say how many people will be harmed by taking such a high dose, but I know with certainty that toxicity at that dose is not rare, because I see it all the time. Some people can take very high doses and be just fine, calcium stays normal. Others will take 5000 units daily and end up with high calcium, and all the symptoms that go along with that (including kidney stones, fatigue, cardiac arrhythmias, etc). Now I am not saying that NO ONE should take high dose Vit D. Some people actually need that high dose, but that is only in the case of someone with very low Vit D and low calcium levels - often in someone who has problems with intestinal absorption, as you would see in someone who had a gastric bypass, for example.