Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency -: A dose-finding trial

Background: Supplementation with high doses of oral cobalamin is as effective as cobalamin administered by intramuscular injection to correct plasma markers of vitamin B-12 deficiency, but the effects of lower oral doses of cobalamin on such markers are uncertain. Methods: We conducted a randomized, parallel,Group, double-blind, close-finding trial to determine the lowest oral dose of cyanocobalamin required to normalize biochemical markets of vitamin B-12 deficiency in older people with mild vitamin B-12, deficiency, defined as a serum vitamin B-12 level of 100 to 300 pmol/L (135-406 pg/mL) and a methylmalonic acid level of 0.26 mu mol/L or Greater. We assessed the effects of daily oral doses of 2.5, 100, 250, 500, and 1000 mu g of cyanocobalamin administered for 16 weeks on biochemical markets of vitamin B-12 deficiency in 120 people. The main outcome measure was the dose of oral cyanocobalamin that produced 80% to 90% of the estimated maximal reduction in the plasma methylmalonic acid concentration. Results: Supplementation with cyanocobalamin in daily oral closes of 2.5, 100, 250, 500, and 1000 mu g was associated with mean reductions in plasma methylmalonic acid concentrations of 16%, 16%, 23%, 33%, and 33%, respectively. Daily doses of 647 to 1032 mu g of cyanocobalamin were associated with 80% to 90% of the estimated maximum reduction in the plasma methylmalome acid concentration. Conclusion: The lowest dose of oral cyanocobalamin required to normalize mild vitamin B-12 deficiency is more than 200 times greater than the recommended dietary allowance, which is approximately 3 mu g daily.