[bird_monster]

It would probably be wise to not post your opinion on things like vitamin dosages unless you're a medical doctor.

My doctor prescribed 1 week of 15000 IU a day, then a week of 10000 IU, then a running dose of 5000 IU a day. I've seen measurements of 50k IU from a day in the sun. 3000-5000 is not too much or "obscenely high" for many people, but as with literally everything like this, its best to consult a doctor about an individual's needs.

[nn3]

Why? The younger doctor is likely just reading wikipedia too.

And the older ones are probably just telling you what was the conventional wisdom when they did their education 20 years ago.

[bird_monster]

You're asking "Why" as in "Why shouldn't we listen to untrained professionals' opinions on supplement dosages" ?

Also this person did not wikipedia what they posted, as wikipedia also lists tolerable upperbounds for adults as 4000 IU / day.