The luxus vitamins--A and B12.

It is proposed that for vitamin A and vitamin B12 alone among the known micronutrients a luxus (excessive) intake habitually exists. Evidence for this is presented by a comparison of habitual intake with Recommended Dietary Allowance and of total body content in relation to requirements. Both vitamins accumulate in the liver with increasing age and concentrations relate to dietary intake. "Normal" plasma values have very wide ranges. The loss of these vitamins from the body is exponential and related to body "stores". Their location and chemical forms in the liver are discussed and for vitamin A the stellate cell appears to act as a "stump". A "last come, first served" phenomenon operates for these vitamins, as it does for a number of other substances, and is compatible with a luxus state.