Originally Posted by teaser

D2 is a different form entirely. We make vitamin D from 7 dehydrocholesterol, it's sort of a precursor for what we usually call "cholesterol" as well. The sun doesn't protect kittens from rickets unless they have a dietary source of 7 dehydrocholesterol, so it's sort of conditionally essential along with vitamin D for them, that always makes me wonder if a dietary source of this cholesterol precursor might help us when we get older--food sources that aren't that high in vitamin D itself might help anyways on that front. I understand mice are an excellent source.