Vitamin B₁₂ is also called cobalamin. We need vitamin B₁₂ in our daily diet to help the cells in our bodies grow and maintain normal function. It is an especially important vitamin for healthy bone marrow (where blood cells are formed) and the nervous system. Not getting enough vitamin B₁₂ leads to a disease called pernicious anemia, which results in red blood cells not getting enough oxygen and causing disorders of the nervous system. The elderly are at higher risk for developing pernicious anemia because aging causes a decrease in the amount of vitamin B₁₂ that the body is able to absorb from food.

The most important use of vitamin B₁₂ is to improve the symptoms of pernicious anemia. These symptoms include weakness, pallor, and neurologic symptoms such as burning or prickling of the hands and feet, loss of balance, confusion, loss of memory, and moodiness.

Recent studies suggest a role for vitamin B₁₂ in the prevention of heart disease. Patients taking a combination of folic acid, vitamin B₁₂, and vitamin B₆ lowered their blood levels of homocysteine, a substance that seems to be associated with a higher risk of heart disease.

Vitamin B₁₂ is present in foods containing animal protein. The richest sources of it are liver and kidney. Other good sources of vitamin B₁₂ include milk, eggs, fish, and cheese.

Vitamin B₁₂ can be found in vitamin form as cyanocobalamin. It is available as tablets, softgels, or lozenges in multivitamin form (including children's chewable and liquid drops), B-complex form, or by itself.

People whose daily diet includes meat, milk, and other dairy products should be able to meet the recommended daily requirements without taking a vitamin supplement. Vegetarians who do not eat any animal protein should take a vitamin B₁₂ supplement with water, preferably after eating. Elderly people may need more vitamin B₁₂ because of decreased ability of the body to absorb vitamin B₁₂ from the diet as we age. People considering supplements should check with their healthcare provider to find out what dosage best fits their needs.

As with all supplements, check with your healthcare provider before giving vitamin B₁₂ to a child.

Daily recommendations for dietary vitamin B12 are listed below.

Pediatric

• Neonates to 6 months.: 0.4 mcg (adequate intake)
• Infants 6 months to 1 year: 0.5 mcg (adequate intake)
• Children 1 to 3 years: 0.9 mcg (RDA)
• Children 4 to 8 years: 1.2 mcg (RDA)
• Children 9 to 13 years: 1.8 mcg (RDA)
• Adolescents 14 to 18 years: 2.4 mcg (RDA)

Adult

• 19 years and older: 2.4 mcg (RDA)
• Pregnant females: 2.6 mcg (RDA)
• Breastfeeding females: 2.8 mcg (RDA)

Vitamin B₁₂ is non-toxic, but there is no known benefit to healthy individuals of taking more than the 2.0 mcg recommended daily allowance.

The body's ability to absorb vitamin B₁₂ is decreased when taking medications such as omeprazole, lansoprazole, ranitidine, cimetidine, or antacids that are often used to treat ulcers. This interference is most likely to result from prolonged use of these medications more than a year.

Vitamin B₁₂ should not be taken at the same time as tetracycline, an antibiotic, because it interferes with the absorption and effectiveness of this medication. Vitamin B₁₂ either alone or in combination with other B vitamins should be taken at different times from tetracycline.

Blood levels of vitamin B₁₂ may also be reduced when taking metformin for diabetes or chemotherapy medications for cancer, particularly methotrexate.

Long-term treatment with phenobarbital and phenytoin may interfere with the body's ability to use vitamin B₁₂.

Ballal RS, Jacobsen DW, Robinson K. Homocysteine: update on a new risk factor. Cleve Clin J Med. 1997;64:543–549.

Carmel R. Cobalamin, the stomach and aging. Am J Clin Nutr. 1997;66(4):750-759.

Committee on Dietary Allowances. Recommended Dietary Allowances. National Academy of Sciences. Accessed at www.nal.usda.gov/fnic/Dietary/rda.html on January 8, 1999.

Dastur D, Dave U. Effect of prolonged anticonvulsant medication in epileptic patients: serum lipids, vitamins B₆, B₁₂ and folic acid, proteins and fine structure of liver. Epilepsia. 1987;28:147-159.

Dorland Newman WA, ed. Dorland's Illustrated Medical Dictionary. 28th ed. Philadelphia, Pa: WB Saunders Co; 1994:73.

Ekhard ZE, Filer LJ, eds. Present Knowledge in Nutrition. 7th ed. Washington, DC: ILSI Press; 1996:191–201.

Hardman JG, Limbird LE, eds. Goodman and Gillman's The Pharmacological Basis of Therapeutics. 9th ed. New York, NY: McGraw-Hill; 1996:1326–1333.

Howden CW. Vitamin B12 levels during prolonged treatment with proton pump inhibitors. J Clin Gastroenterol, 1999;30(1):29-33.

Hurter T, Reis HE, Borchard F. Disorders of intestinal absorption in patients treated with cytostatic chemotherapy [in German]. Z Gastroenterol. 1989;27(10):606-610.

Ingram CF, Fleming AF, Patel M, Galpin JS. The value of intrinsic factor antibody test in diagnosing pernicious anaemia. Cent Afr J Med. 1998;44:178–181.

Latham J, Gill DS, Wickramasinghe SN. Effects of phenytoin sodium on doubling time, deoxyuridine suppression, 3H-methotrexate uptake and 57C0-cyanocobalamin uptake in HL60 cells. Clin Lab Haematol. 1990;12(1):67-75.

Lobo A, Naso A, Arheart K, et al. Reduction of homocysteine levels in coronary artery disease by low-dose folic acid combined with levels of vitamins B6 and B12. Am J Cardiol. 1999;83:821–825.

Lee AJ. Metformin in noninsulin-dependent diabetes mellitis. Pharmacotherapy. 1996;16:327–351.

Mahan LK, Arlin MT, eds. Krause's Food, Nutrition, and Diet Therapy. 8th ed. Philadelphia, Pa: WB Saunders Co; 1992:96–97.

National Research Council. Recommended Dietary Allowances. 10th ed. Washington, DC: National Academy Press; 1989:158–165.

Nilsson-Ehle H. Age-related changes in cobalamin (vitamin B12) handling. Implications for therapy. Drugs Aging. 1998;12:277–292.

Nutrients and Nutritional Agents. In: Kastrup EK, Hines Burnham T, Short RM, et al, eds. Drug Facts and Comparisons. St. Louis, Mo: Facts and Comparisons; 2000:4-5.

Omray A. Evaluation of pharmacokinetic parameters of tetracylcine hydrochloride upon oral administration with vitamin C and vitamin B complex. Hindustan Antibiot Bull. 1981;23(VI):33-37.

Remacha AF, Cadafalch J. Cobalamin deficiency in patients infected with the human immunodeficiency virus. Semin Hematol. 1999;36:75–87.

Schumann K. Interactions between drugs and vitamins in advanced age. Int J Vitam and Nutr Res, 1999;69(3):173-178.

Termanin B, Gibril F, Sutliff VE, Yu F, Venzon DJ, Jensen RT. Effect of long-term gastric acid suppressive therapy on serum vitamin B12 levels in patients with Zollinger-Ellison syndrome. Am J Med. 1998;104(5):422-430.

van Asselt DZ, van den Broek WJ, Lamers CB, et al. Free and protein-bound cobalamin absorption in healthy middle-aged and older subjects. J Am Geriatr Soc. 1996;44:949–953.