Vitamin C: from popular food supplement to specific drug.

The daily requirement of a human person for vitamin C (ascorbic acid) has now been established at 100 mg. This value was already on the map when Arnold Durig put together the most important needs of nutritional ingredients. The modern value rests on the saturating level of ascorbate in leukocytes, which is in the millimolar range. The mechanism of accumulation of ascorbate in these cells rests on the uptake of oxidized dehydroascorbic acid. It is very efficient and avoids loss of vitamin which occurs in vitro when ascorbate is oxidized because of the great instability of the dehydro form. Therefore and increased requirement in case of infection is very unlikely from the biochemical point of view. However, low concentrations of ascorbate are found in patients suffering from arterial diseases or diseases accompanied by arterial damage such as diabetes mellitus. Ascorbate is known as a protection factor for the arterial endothel, but it is not clear by what mechanism this protection is brought about. Moreover, under clinical conditions very high concentrations are needed, which are achieved only by intravenous infusion, and the protection is only observed when the disease is manifest, not in healthy people. Therefore, also in this respect an increase in daily intake seems of no prophylactic value. Thus, by using high concentrations of ascorbate as an i.v. drug, effects of this substance frequently observed in vitro, could be used for therapy. This includes not only treatment of arterial diseases, but also relates to the cytotoxic effects of the vitamin against certain tumor cells and may assist conventional chemotherapy.