To the Editor.—
The plasma absorption of vitamin B12 in man following oral administration of physiologic doses of crystalline radioactive cobalt-labeled cyanocobalamin has been known for many years.1-3 The absorption curve shows a delay in appearance of radioactivity for 3 to 4 hours, followed by a rapid rise to a maximum 8 to 12 hours after ingestion of the test dose. The subsequent falloff is gradual over a period of days. Since vitamin B12 in nature is present in coenzyme forms4,5 and bound to proteins,6 the question was raised whether vitamin B12 in food is absorbed into the blood in a manner similar to that of crystalline radioactive cobalt-labeled cyanocobalamin.We have tried to answer this question by studying the plasma absorption of radioactive isotope-labeled cyanocobalamin incorporated into food in vivo. An egg-laying hen was injected with cyanocobalamin Co 57, and the radioactive eggs
DOSCHERHOLMEN A, McMahon J, Ripley D. Plasma Absorption of Vitamin B12 in Food. JAMA. 1974;227(7):800. doi:10.1001/jama.1974.03230200058018
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