title: Holo-transcobalamin is an indicator of vitamin B-12 absorption in healthy adults with adequate vitamin B-12 status.
abstract: 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.
  
  
  METHODS
  Adult (18-49 y) male and female participants (n = 21) with normal vitamin B-12 status were given three 9-mug 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-mug 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-mug doses of vitamin B-12 should run for 24 h.
authors.affiliation: Departments of Food Science and Human Nutrition, University of Florida, Gainesville, USA.
authors.forename: Kristina M
authors.initials: KM
authors.lastname: von Castel-Roberts
authors.forename: Anne Louise
authors.initials: AL
authors.lastname: Morkbak
authors.forename: Ebba
authors.initials: E
authors.lastname: Nexo
authors.forename: Claire A
authors.initials: CA
authors.lastname: Edgemon
authors.forename: David R
authors.initials: DR
authors.lastname: Maneval
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Shuster
authors.forename: John F
authors.initials: JF
authors.lastname: Valentine
authors.forename: Gail P A
authors.initials: GP
authors.lastname: Kauwell
authors.forename: Lynn B
authors.initials: LB
authors.lastname: Bailey
mesh_terms: D000042:Absorption; D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D019540:Area Under Curve; D015415:Biomarkers / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009752:Nutritional Status; D013997:Time Factors; D014155:Transcobalamins / Q000032:analysis* / Q000378:metabolism; D014805:Vitamin B 12 / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D014803:Vitamin B Complex / Q000008:administration & dosage* / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D015415:Biomarkers; D014155:Transcobalamins; D014803:Vitamin B Complex; D014805:Vitamin B 12