D3 is preferred to D2. http://www.medscape.com/viewarticle/589256_4

My wife's blood work showed low D levels. Dr. recommended starting with 6000 IU/day for a couple months, then tapering down to 2,000 IU, which we did. Her blood levels are now normal. This is not too surprising: we live in the PNW and are religious abut using long sleeves and/or sunscreen when it is sunny. I did the same as she. We've now been taking 2,000 IU/day for a few years, no damage .