vitamin d from sunlight foods and even vitamin supplements is not biologically active. it has to undergo two processes the first occurring in the liver which converts vitamin d to the 25(oh)d form also known as calcidiol or vitamin d². the kidney then makes the most active form 1 25(oh)²d also known as calcitriol or vitamin d³. if you check your bottle of vitamins or calcium + vitamin d supplements you can see which type you have been taking. currently the preferred supplement form may be vitamin d³ as it increases the amount of active vitamin d while increasing the time vitamin d is active in the blood and tissues.
is all vitamin d the same?