Oral Cyanocobalamin Supplementation in Older People With Vitamin B12 Deficiency

duced 80% to 90% of the estimated maximal reduction in the plasma methylmalonic acid concentration. Results: Supplementation with cyanocobalamin in daily oral doses of 2.5, 100, 250, 500, and 1000 µg was asso- ciated with mean reductions in plasma methylmalonic acid concentrations of 16%, 16%, 23%, 33%, and 33%, respectively. Daily doses of 647 to 1032 µg of cyanoco- balamin were associated with 80% to 90% of the esti- mated maximum reduction in the plasma methylmalo- nic acid concentration. Conclusion: The lowest dose of oral cyanocobalamin re- quired to normalize mild vitamin B12 deficiency is more than 200 times greater than the recommended dietary al- lowance, which is approximately 3 µg daily. Arch Intern Med. 2005;165:1167-1172