The Effect of Megadose Ascorbic Acid Ingestion on the Absorption and Retention of Vitamin B 12 in Man

Abstract

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 absorbic 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 hydroxycobalamin 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.