Evidence Concerning the Human Requirement for Vitamin B12

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Abstract
An example of the use of the whole body counter as a safe, simple and accurate means of assessment of absorption, distribution and excretion of a metabolite, vitamin B12, is presented. Results of absorption studies in five subjects without pernicious anemia and eighteen patients with pernicious anemia are presented. The range of absorption in the subjects without pernicious anemia is 45 to 80 per cent with a mean of 70 per cent and in those with pernicious anemia 0 to 17 per cent with a mean of 3.25 per cent. Studies of biological half-life of vitamin B12 are presented in sixteen subjects (eleven with pernicious anemia and five without), including three normal subjects, who have been observed for as long as two years. There was no significant difference in decay constants between those with pernicious anemia and the normal subjects. The values ranged from 0.09 to 0.15 per cent loss per day of labeled vitamin in normal subjects, and from 0.11 to 0.17 per cent loss per day in eleven patients with pernicious anemia. These figures correspond to a biological half-life of 407 to 770 days. The proposal is made and support cited for the concept that the daily need for injectable vitamin B12 in patients with pernicious anemia reflects almost entirely the loss of the vitamin from the body. Despite the marked difference in the size of the body stores of vitamin B12 in normal subjects and in those with pernicious anemia, daily loss rate constants are essentially identical. Parameters are identified which require study before dietary requirements levels can be set more precisely.