D3 — one would get enough IF they were out in the sun long enough.
In northern latitudes this would have to be in the summer, and for even as much as 20 minutes, as I recall hearing.
So then it would be needed especially in the winter.
It would be hard to take too much. Doctors take 4,000 or more.
Bits I have heard over time. I image a SEARCH would yield a lot of info on this.
I bought vitamin d gummies for the kids - Nordic Naturals brand. They love them. They are so good my 5 year old snuck the bottle out of the kitchen and ate the whole thing. There were probably only 20-30 left so I figured he got one week of a prescription level dose. I didn’t worry about an overdose because, as you said, it would be hard to take too much.
They really are that good. My kids love their multi vitamin gummies as well (Nordic Berries) but are much too expensive for us to take regularly.