American Journal of Clinical Nutrition, Vol 14, 156-162, Copyright © 1964 by The American Society for Clinical Nutrition, Inc.

Long-Term Excretion of Co⁵⁷-Vitamin B₁₂ and Turnover Within the Plasma

¹ From the Radioisotope and Medical Services, Albany Veterans Administration Hospital, Albany, New York

Eight control subjects were given an average of 1.0 µg. of Co⁵⁷-vitamin B₁₂ by different routes. The Co⁵⁷ in plasma, urine and feces was measured for at least seventy days in all subjects and for more than 500 days in half of them with the following results:

(1) The Co⁵⁷-vitamin B₁₂ disappeared rapidly from the plasma in a complex manner until about day 70. Subsequently, the loss could be described by a linear function with an average half-time of 690 days.

(2) Urinary excretion was higher the first few days than subsequently regardless of route of intake. Fecal excretion did not become uniform until about one month after intravenous administration.

(3) Urinary excretion during the period of uniform loss was 0.028 per cent of the retained dose per day. Simultaneous fecal excretion was 0.031 per cent per day. Comparison of urinary excretion of Co⁵⁷ and total vitamin B₁₂ as measured by microbiological assay suggested that only 10 per cent of the vitamin B₁₂ excreted in the urine was in an active form.

(4) The total daily excretion of vitamin B₁₂ was calculated to be 0.66 to 2.1 µg., mean 1.3 µg.