Publications
Bioavailability and daily requirement of vitamin B(12) in adult humans: an observational study of its colonic absorption and daily excretion as measured by [(13)C]-cyanocobalamin kinetics.
Kurpad, Anura V.; Pasanna, Roshni M.; Hegde, Shalini G.; Patil, Mallikarjun; Mukhopadhyay, Arpita; Sachdev, Harshpal S.; Bhat, Kishor G.; Sivadas, Ambily; Devi, Sarita BACKGROUND: Clinical and biochemical vitamin B(12) (B(12)) deficiency is lower than anticipated in vegetarians. Extraileal absorption, such as from the colon, as well as reduced daily excretion, may be adaptive mechanisms to maintain B(12) homeostasis with marginal intakes. OBJECTIVE: To measure the absorption of B(12) from the small and large intestine, and its daily rate of excretion from the body, using a [(13)C]-cyanocobalamin tracer. METHODS: Oral B(12) bioavailability was measured over 12 h after administration of [(13)C]-cyanocobalamin tracer (2.5 μg) in normal participants. The colonic B(12) bioavailability was evaluated by direct instillation of [(13)C]-cyanocobalamin (5 μg) into the ascending colon. Bioavailability was calculated from 2-compartmental modeling of the tracer appearance in plasma. The excretion rate of B(12) was measured from [(13)C]-cyanocobalamin elimination from the body over 4 wk after oral dosing (5 μg). RESULTS: The oral B(12) bioavailability (n = 11) was 63% ± 10% measured over 12 h. A late absorption peak, accounting for 12% of the absorption, was observed after an average lag time of 8.7 h from dosing. The colonic B(12) bioavailability (n = 10) was 7% ± 5% over 4 h. The daily B(12) excretion rate (n = 4) was 0.7 ± 0.2 μg/d. The minimum daily requirement of B(12) in these participants was derived at 1 μg /d. CONCLUSIONS: B(12) is absorbed in the human colon. This observation confirms the potential contribution of the colon in daily B(12) nutriture, and along with a possible lower requirement, could explain the absence of clinical deficiency in populations with marginal B(12) intakes. TRIAL REGISTRATION NUMBER: This study was registered in Clinical Trials Registry of India (CTRI) with the registration number CTRI/2018/04/012957, available from https://ctri.nic.in/Clinicaltrials/showallp.php?mid1=49319&EncHid=&userName=029108.
