Increases in Plasma Holotranscobalamin Can Be Used to Assess Vitamin B-12 Absorption in Individuals with Low Plasma Vitamin B-12

Low plasma concentrations of vitamin B-12 are common in Indians, possibly due to low dietary intakes of animal-source foods, Whether malabsorption of the vitamin contributes to this has rot been investigated. A rise in the plasma holotranscobalamin (holo-TC) concentration after a standard dose of oral vitamin B-12 has been proposed as a measure of gastrointestinal absorption in people with normal plasma vitamin B-12 concentrations. We studied 313 individuals (children and parents, 109 families) in the Pune Maternal Nutrition Study. They received 3 doses of 10 mu g (n = 191) or 2 mu g (n = 122) of cyanocobalamin at 6-h intervals. A rise in plasma holo-TC of >= 15% and >15 pmol/L above baseline was considered normal vitamin B-12 absorption. The baseline plasma vitamin B-12 concentration was <150 pmol/L in 48% of participants; holo-TC was <35 pmol/L in 98% and total homocysteine was high in 50% of participants (>10 mu mol/L in children and >15 mu mol/L in adults). In the 10 mu g group, the plasma holo-TC concentration increased by 4.8-fold from (mean +/- SO) 9.3 +/- 7.0 pmol/L to 53.8 +/- 25.9 pmol/L and in the 2 mu g group by 2.2-fold from 11.1 +/- 8.5 pmol/L to 35.7 +/- 19.3 pmol/L. Only 10% of the participants, mostly fathers, had an increase less than the suggested cut-points. Our results suggest that an increase in plasma holo-TC may be used to assess vitamin B-12 absorption in individuals with low vitamin B-12 status. Because malabsorption is unlikely to be a major reason for the low plasma vitamin B-12 concentrations in this population, increasing dietary vitamin B-12 should improve their status. J. Nutr. 139: 2119-2123, 2009.