I recently had an annual visit with my Urologist, (new to me as my old one retired) and he mentioned that My taking a D3 supplement (2000 iu) was not doing a lot of good because the body has a hard time absorbing D3. He said the best source for D3 was the Sun but that would require us to run around naked 20 hours a day in the Sun. (you can, I'm not) So he put me on 25mg of D2 and said that the body can convert and easily absorb what it needs. I've never heard this before and i wonder if anyone else has. I thought that was a pretty high dose.