If you have Kindle unlimited, read a few of the many books on vitamin D: https://www.amazon.com/s?k=vitamin+d+book
This is a good one:
THE MIRACULOUS RESULTS OF EXTREMELY HIGH DOSES OF THE SUNSHINE HORMONE VITAMIN D3 MY EXPERIMENT WITH HUGE DOSES OF D3 FROM 25,000 to 50,000 to 100,000 IU A Day OVER A 1 YEAR PERIOD by Jeff T Bowles
No link. Texags has gone into it more than once.
Reville (DR) recommends not to be deficient but dont do a hammer.
If you search around you can find the studies. It is controversial. You will see studies come down on both sides of the issue
Since I witnessed it first hand I err on the side of caution. Just like with Elderberry