The point wasn't the dose, I just picked a number out of my ass.

The point is that from that N IU the 100 people will absorb anything from 0-N, it's very individual and varied.

The only way to be sure is to test your levels, which costs money every time. There really should be a simple and cheap home test kit for it. You'd sell millions every year just in the Nordics and Canada =)

Maybe this comes across snide, but have you been to the Nordics? I can get tested at my GP for free practically as often as I'd like, I doubt you'd sell too much in the way of home test kits.

Been living here my whole life.

I've been offered a (free) Vitamin D checkup exactly zero times. We should be getting them though, dunno why we don't.

i'm guessing he meant 50k not 50. 50k is quite a large dose.

There is no way that's what they meant. 50k is an absurdly large dose that's way outside the safe intake range. 10k is used sometimes under medical supervision and even then it's a very short term measure. For long term intake, 4000IU is a widely accepted safe upper limit. 50k is an order of magnitude more than that.

There's plenty of documentation of people taking 50k for a period of time and having no side effects. There's been something like a dozen trials using high doses like this to treat TB, and they're usually successful, with no significant negative symptoms.

Conversely, some studies have shown that 4k IU does contribute to hypercalcemia in a small number of cases (4 per 1000). So actually 4k is deemed "not completely safe" as a limit.

The point is, the amount you take needs to be adjusted by a clinician, as the safe range for you is unknowable otherwise.