Recently, I went shopping for vitamin D supplements and I was surprised by the very wide range in products marketed for daily usage, going from 600 IU to 12,000 IU.

The recommended intake and upper limit vary depending on which country's ministry of health or which non-governmental health organisation you ask.

The Mayo Clinic places toxicity at 50,000 IU [1] and there is anecdotal evidence (i.e. unverifiable comments from the EFSA public consultation on vitamin D) of individuals taking up to 100,000 IU a day.

[1]: https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h...

My doc recommended that I take 10K IU/day. That's the very upper end of the new (higher) range. (I only take 5k, and believe it's incredibly helpful for my mental health.)

My doctor prescribed me 10000 IUs/day, which seems to be pretty high based on the values listed in the article. I had a D deficiency at the time, but he suggested that I continue those doses as "preventative maintenance" in the future, even after my levels returned to normal.

I assume that it's just a consequence of normal variation regarding (A) the journals your doctor is reading and (B) how they're interpreting those articles.

Did you mean "prescribed"? "Proscribed" means forbidden.