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Holo-transcobalamin is an indicator of vitamin B-12 absorption in healthy adults with adequate vitamin B-12 status^1,2,3

¹ From the Departments of Food Science and Human Nutrition (KMvCR, CAE, DRM, GPAK, and LBB), Health Policy and Epidemiology (JJS), and Medicine (JFV), the General Clinical Research Center (JJS), University of Florida, Gainesville, and the Department of Clinical Biochemistry, Nørrebrogade, Aarhus Sygehus, Aarhus, Denmark (ALM and EN)

Background:It has been hypothesized that the response of holo-transcobalamin (holo-TC) to oral vitamin B-12 may be used to assess absorption. To develop a reliable clinical absorption test that uses holo-TC, it is necessary to determine the optimal timeline for vitamin B-12 administration and postdose assessment.

Objective:The objective of this study was to assess the magnitude and patterns of change in the postabsorption response of holo-TC to oral vitamin B-12.

Design:Adult (18–49 y) male and female participants (n = 21) with normal vitamin B-12 status were given three 9-µg doses of vitamin B-12 at 6-h intervals beginning early morning (baseline) on day 1. Blood was drawn at 17 timed intervals over the course of 3 d for the analysis of holo-TC and other indicators of vitamin B-12 status.

Results:Mean holo-TC increased significantly (P < 0.001) from baseline at 6 h (11%) and 24 h (50%). TC saturation increased significantly (P < 0.001) from baseline at 12.5 h (33%) and 24 h (50%). The mean cobalamin concentration changed significantly (P < 0.001) from baseline at 24 h (15%) and 48 h (14%). The ratio of holo-TC to cobalamin increased significantly (P < 0.001) at 24 h (32%).

Conclusions:The greatest increase in holo-TC was observed 24 h after ingestion of three 9-µg doses of vitamin B-12. Our results indicate that a vitamin B-12 absorption test based on measurement of holo-TC after administration of three 9-µg doses of vitamin B-12 should run for 24 h.

Key Words: Transcobalamin • holo-transcobalamin • holo-TC • vitamin B-12 • vitamin B-12 absorption • healthy adults

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