Daily intake of 4 to 7 μg dietary vitamin B-12 is associated with steady concentrations of vitamin B-12-related biomarkers in a healthy young population

Background: Studies have questioned whether the current Recommended Dietary Allowance (RDA) of 2.4 mu g vitamin B-12/d is adequate. Objective: We examined the association between dietary vitamin B-12 intake and biomarkers of vitamin B-12 status. Design: Dietary vitamin B-12 intake was estimated, and biomarkers of vitamin B-12 status were measured, in healthy men and women (n = 299; age range: 18-50 y) who were recruited from a Florida community. The National Cancer Institute Diet History Questionnaire was used. Plasma cobalamin, total transcobalamin, holotranscobalamin, methylmalonic acid (MMA), total homocysteine (tHcy), and autoantibodies against intrinsic factor (IF) and Helicobacter pylori were analyzed in blood samples. Results: Antibodies to H. pylori were detected in 12% of subjects (35/299), and negative results for IF antibodies were obtained for all subjects. The intake of vitamin B-12 correlated significantly with cobalamin, holo-transcobalamin, MMA, and tHcy. Subjects were divided into quintiles on the basis of their dietary vitamin B-12 intake (range: 0.42-22.7 mu g/d), and biomarkers of vitamin B-12 status were plotted against estimated dietary vitamin B-12 intake. All biomarkers appeared to level off at a daily dietary vitamin B-12 intake between 4.2 and 7.0 mu g. Conclusion: In persons with normal absorption, our data indicate that an intake of 4-7 mu g vitamin B-12/d is associated with an adequate vitamin B-12 status, which suggests that the current RDA of 2.4 mu g vitamin B-12/d might be inadequate for optimal biomarker status even in a healthy population between 18 and 50 y of age. Am J Clin Nutr 2010;91:571 7.