The effect of megadose ascorbic acid ingestion on the absorption and retention of vitamin B12 in man.

Radiotracer B12 analogues, hydroxy- and cyano-cobalamin have been used to study the effects of megadose L-ascorbic acid (vitamin C) ingestion on vitamin B12 metabolism in man. By employing whole body counter techniques it has been shown that, while ascorbic acid can partially inactivate both the important dietary analogue, hydroxycobalamin, and the gastric secretion, intrinsic factor which is essential for B12 absorption, the rapid binding of the B12 analogue to intrinsic factor protects the hydroxycobalamin from attack. As a result, the absorption of hydroxcobalamin is unaffected by the simultaneous ingestion of 1 g ascorbic acid. The absorption of cyanocobalamin, the most stable analogue but not found in quantity in the diet, is slightly increased by ascorbic acid. Whole body retention studies on normal subjects ingesting 2 g ascorbic acid per day show no significant evidence of in vivo destruction of body B12 stores.