I know that a major issue is that vitamins and minerals can degrade each other if stored long term together - mixed up. Metabolically, they perform very different functions. Minerals are part of muscle functions, and bone make up. Vitamins often have the simple function of completing the final structure of an enzyme.
They are both present in the body, in some quantities, at all times. Having very low doeses in the body at the same time is probably not going to bother anything in there, as long as balance is maintained.
Animals in the wild are not restricted the way captive animals are - the content of their diets goes all over the place. Preformed D3 is a part of their natural diet, as is preformed vitamin A - how they get it is anyone's guess. It could be form an occational vertebrate liver, a bug that had eaten a vertebrate liver - who the heck knows. Somewhere, some times, they will eat it.
Same with D3 - animals that have D3 in their system and are eaten themselves are a way for them to get it. It's not JUST form the sun - I was told that grasshoppers, full of grass, have a high dietary D3 content. Of course, I was told - not "shown". Hehe. Anyone got data on that?
I have never had an issue with D3 or A being out of balance when I was giving them everything in low doses. Many friends of mine have been "cautious" with D3 and A, and prefer to avoid all artificial supplementations - just ot be careful. More often than not, they have had to treat a problem that was DUE to a vitamin imbalance. The treatment is usually the addition of a dietary supplement.
I'd prefer an all-natural diet for them, if possible. UVB helps bring it all that much closer. However, replication of ALL the natural foods they get and need is 100% impossible for most of us, if not all of us. A teeny eeny bit of artificial vitamins here and there will make up for any crucial gaps in their dietary requirements we may miss.
For humans, without a dietary issue, vitamins are worthless.
For reptiles, which have been thrust into captivity, and given an artificial diet, I believe they are usually necessary to fill the gaps.
I never take vitamins myself - I know how they work, and I know why they work, and I know why they're a waste for people - but I give them to my animals because I am confident that no matter how hard I try to replicate their natural diet, I will be wrong.
Playing it safe is giving them a tiny bit every oncei n a while.
That's my opinion, anyway!
Eric A
