Lara provided this wonderful link about Vit D treatment in
Australia...

http://www.abc.net.au/catalyst/stories/2514231.htm

Please watch the video. They are using 4000IU daily for D3 to raise levels, rather than what the US is doing with D2 at 50,000 IU.

The reason US doctors are doing the 50,000IU is that D2 (ergocalciferol) was the only form we had for decades to treat rickets. It is the only RX form of Vit D we have, so doctors naturally look in their therapeutic references (you know this is where treatments are decided) and bingo, that is what you get.

Very few doctors (except those who make the extra effort to learn) know about the differences in D products.
It is not unlike the cyanocobalamin/methylcobalamin issues.
And similar to folic acid/methylfolate and pyridoxine/P5P.
As the past 10 yrs have unfolded, the researchers in nutrition have outpaced the doctors quite a bit.
That is why D3 is OTC, and we are seeing more attention to the other activated forms of other vitamins.
And I might add that there are many pharmacists too who don't know the difference so don't expect a good answer to this question in many pharmacies either.