Try to find cases in the literature; you'll find cases of people taking orders of magnitude more than that for a month. But nothing serious from anyone taking 50k IUs/day, let alone per week.
I get your point that the studies are limited at such high doses, but Mayo clinic and various others disagree that it's non-toxic.
"Taking 50,000 international units (IU) a day of vitamin D for several months has been shown to cause toxicity" [1]
Regardless of that though, I agree that the UL is really difficult to quantify. Furthermore I'm not sure anyone could cite any article that shows a significant health benefit to supplementing above 10k vs below, hence, the rational choice would be to try stay below that.
However all of this talk about IU intake is secondary to the blood serum level. For the moment, that is the gold standard measure, until something something better comes along
Definitely agree with blood serum levels. In fact, I should get that done soon! :)
As far as really difficult, in Canada, ingesting enough pills to get to 50,000 IUs per day would be a chore. IIRC the last I checked the biggest OTC doses were 1,000 IUs. This might be different where you are.
