Something to think about: In order to maintain adequate vitamin D levels to maintain healthy blood levels you need to be out in the sun for about 20 minutes everyday (can be up to 6x longer for people with dark skin), in shorts and a t-shirt, mid-day when the the sun’s at its highest. In this time it is possible to make between 10,000 and 20,000 iu of vitamin D. Makes me think, “then why is the (Canadian) RDA only 400-800 iu”. – J Bone Miner Res. 2007 Dec; 22 (Suppl 2): V28-33.