American Journal of Clinical Nutrition, Vol 11, 568-573, Copyright © 1962 by The American Society for Clinical Nutrition, Inc.

Evidence Against Preferential Intestinal Absorption of Physiologic Quantities of Liver-Bound Vitamin B₁₂ by Patients with Pernicious Anemia

¹ From the Thorndike Memorial Laboratory and Second and Fourth (Harvard) Medical Services, Boston City Hospital; and the Department of Medicine, Harvard Medical School, Boston, Massachusetts; and the Department of Internal Medicine and Gustaf V Research Institute, Karolinska Sjukhuset, Stockholm, Sweden

The absorption of physiologic quantities (1.47 µg.) of liver-bound vitamin B₁₂ was compared with the absorption of free cyanocobalamin (2 µg.) in seven subjects with pernicious anemia. Urinary excretion of radiovitamin B₁₂ was determined in five subjects, hepatic uptake in three subjects, and therapeutic trial in one subject. There was no evidence for preferential absorption of liver-bound vitamin B₁₂. Liver-bound vitamin B₁₂ absorption was enhanced by intrinsic factor, suggesting it becomes free of its liver bond in the intestine.

In vitro studies, using both a liver homogenate and a guinea pig gut homogenate system, also indicated no preferential uptake of liver-bound vitamin B₁₂.

The apparent preferential absorption of liver-bound vitamin B₁₂ in the original study, may be explainable, as considered in the original report, by delayed excretion rather than enhanced absorption of liver-bound vitamin B₁₂, which is in a noncyano form, or to possible increased absorption by diffusion in acute vitamin B₁₂-deficiency of the supraphysiologic quantities of vitamin B₁₂ administered. No such increased absorption by diffusion was demonstrated in the patient undergoing therapeutic trial in the present study, however, using a "physiologic" quantity of liver-bound vitamin B₁₂.