Vitamin B12, also called cobalamin, is one of 8 B vitamins. All B vitamins help the body convert food (carbohydrates) into fuel (glucose), which is "burned" to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body metabolize fats and protein. B complex vitamins are necessary for healthy skin, hair, eyes, and liver. They also help the nervous system function properly.

All the B vitamins are water-soluble, meaning that the body does not store them.

Vitamin B12 is an especially important vitamin for maintaining healthy nerve cells, and it aids in the production of DNA and RNA, the body's genetic material. Vitamin B12 also works closely with vitamin B9 (folate) to regulate the formation of red blood cells and to help iron function better in the body. Folate and B12 work together to produce S-adenosylmethionine (SAMe), a compound involved in immune function and mood.

Vitamins B12, B6, and B9 work together to control blood levels of the amino acid homocysteine. High levels of homocysteine are associated with heart disease. However, researchers aren't sure whether homocysteine is a cause of heart disease or merely a marker that indicates someone may have heart disease.

Mild deficiencies of B12 are not uncommon in elderly people, either because of poor diet or because they have less stomach acid, which the body needs to absorb B12. Low levels of B12 can cause a range of symptoms including fatigue, shortness of breath, diarrhea, nervousness, numbness, or tingling sensation in the fingers and toes. Severe deficiency of B12 causes neurological damage.

Others at risk for B12 deficiency include:

• Vegans (vegetarians who also don't eat dairy or eggs)
• People with malabsorption conditions, such as tapeworm infection, pancreatic disease, and conditions resulting from gastrointestinal surgery
• People who are infected with Helicobacter pylori (an organism in the intestines that can cause an ulcer). H. pylori damages stomach cells that make intrinsic factor, a substance the body needs to absorb B12
• People with an eating disorder
• People with HIV

Folic acid (vitamin B9), especially when taken in high doses, can mask the symptoms of a vitamin B12 deficiency, leading to neurological damage. For that reason, anyone planning to take more than 800 mcg of folic acid should talk to their doctor first, to make sure they do not have a B12 deficiency.

Vitamin B12 is used for:

Pernicious Anemia

Pernicious anemia occurs when stomach cells are not able to make intrinsic factor, and the body cannot absorb vitamin B12. Symptoms include weakness, pale skin, diarrhea, weight loss, fever, numbness or tingling sensation in the hands and feet, loss of balance, confusion, memory loss, and moodiness. Vitamin B12 supplements in high doses, either given as injections or orally, are prescribed to treat pernicious anemia. Pernicious anemia can be a dangerous condition and should always be treated by a doctor.

Heart Disease

Many studies indicate that patients with elevated levels of the amino acid homocysteine are roughly 1.7 times more likely to develop coronary artery disease and 2.5 times more likely to suffer from a stroke than those with normal levels. Homocysteine levels are strongly influenced by B complex vitamins, particularly vitamins B9, B6, and B12.

The American Heart Association recommends that, for most people, an adequate amount of these important B vitamins be obtained from diet, rather than taking extra supplements. Under certain circumstances, however, supplements may be necessary. Such circumstances include elevated homocysteine levels in someone who already has heart disease or who has a strong family history of heart disease that developed at a young age.

Fatigue

A vitamin B12 deficiency causes fatigue. One small study, done a number of years ago, suggested that some people who were not deficient in B12 might gain more energy from B12 injections; however, follow-up studies are needed. One preliminary study indicated that people with chronic fatigue syndrome might benefit from B12 injections, although more research is needed to know for sure.

Breast Cancer

Although there is no evidence that vitamin B12 alone reduces the risk of breast cancer, some population studies have shown that women who get more folate in their diet have lower incidence of breast cancer. Vitamin B12 works with folate in the body, so it may help contribute to a lesser risk. Another preliminary study suggested that postmenopausal women who had the lowest amounts of B12 in their diet had an increased risk for breast cancer.

Male Infertility

Studies suggest that vitamin B12 supplements may improve sperm counts and sperm mobility. However, the evidence is weak. Further studies are needed to determine whether B12 has any real beneficial effect.

Asthma

Some anecdotal evidence suggests that vitamin B12 injections given by a doctor may help treat symptoms of chronic asthma, although scientific studies are lacking.

Vitamin B12 is found only in animal foods. Good dietary sources include fish, dairy products, organ meats (particularly liver and kidney), eggs, beef, and pork.

Vitamin B12 can be found in multivitamins (including children's chewable and liquid drops), B complex vitamins, and individual supplements. It is available in both oral (tablets and capsules) and intranasal forms, softgels, and lozenges. Vitamin B12 is also sold under the names cobalamin and cyanocobalamin.

If your diet includes meat, milk, and other dairy products, you should be able to meet the recommended daily requirements without taking a vitamin B12 supplement. Vegetarians who do not eat any animal protein should take a vitamin B12 supplement with water, preferably after eating. Elderly people may need greater amounts of vitamin B12 than younger people because the body's ability to absorb vitamin B12 from the diet diminishes with age.

People considering B12 supplements should check with a healthcare provider to find out the most appropriate dosage.

Daily recommendations for dietary vitamin B12 are listed below.

Pediatric

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

*Because 10 - 30% of older people may not absorb B12 from food very efficiently, it is recommended that those older than 50 years meet their daily requirement through either foods fortified with vitamin B12 or a supplement containing B12.

Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.

Vitamin B12 is considered safe and non-toxic.

Taking any one of the B complex vitamins by itself for a long period of time can result in an imbalance of other important B vitamins. For this reason, it is generally important to take a B complex vitamin with any single B vitamin. As noted earlier, taking folic acid at high doses can mask a vitamin B12 deficiency, so thse vitamins are often taken together. Talk to your doctor before taking more than 800 mcg of folic acid.

If you are currently being treated with any of the following medications, you should not use vitamin B12 supplements without first talking to your health care provider.

Medications that reduce levels of B12 in the body include:

• Anticonvulsants -- include phenytoin (Dilantin), phenobarbital, primidone (Mysoline)
• Chemotherapy medications -- particularly methotrexate
• Colchicine -- used to treat gout
• Bile acid sequestrants -- used to lower cholesterol; include colestipol (Colestid), cholestyramine (Questran), and colsevelam (Welchol)
• H2 blockers -- used to reduce stomach acid; include cimetidine (Tagamet), famotidine (Pepcid AC), ranitidine (Zantac)
• Metformin (Glucophage) -- medication taken for diabetes
• Proton pump inhibitors -- used to reduce stomach acid; include esomeprazole (Nexium), lansprazole (Prevacid), omeprazole (Prilosec), rabeprazole (Aciphex)

Antibiotics, Tetracycline:Vitamin B12 should not be taken at the same time as tetracycline because it interferes with the absorption and effectiveness of this medication. Vitamin B12 should be taken at different times of the day from tetracycline. (All vitamin B complex supplements act in this way and should be taken at different times from tetracycline.)

In addition, long-term use of antibiotics can deplete vitamin B levels in the body, particularly B2, B9, B12, and vitamin H (biotin), which is considered part of the B complex vitamins.

Abularrage CJ, Sidawy AN, White PW, Aidinian G, Dezee KJ, Weiswasser JM, Arora S. Effect of folic Acid and vitamins B6 and B12 on microcirculatory vasoreactivity in patients with hyperhomocysteinemia. Vasc Endovascular Surg. 2007 Aug-Sep;41(4):339-45.

Adachi S, Kawamoto T, Otsuka M, Todoroki T, Fukao K. Enteral vitamin B12 supplements reverse postgastrectomy B12 deficiency. Ann Surg. 2000;232(2):199-201.

Alpert JE, Fava M. Nutrition and depression: the role of folate. Nutrition Rev. 1997;5(5):145-149.

Alpert JE, Mischoulon D, Nierenberg AA, Fava M. Nutrition and depression: focus on folate. Nutrition. 2000;16:544-581.

Bauman WA, Shaw S, Jayatilleke E, Spungen AM, Herbert V. Increased intake of calcium reverses vitamin B12 malabsorption induced by metformin. Diabetes Care. 2000;13(9):1227-1231.

Booth GL, Wang EE. Preventive health care, 2000 update: screening and management of hyperhomocysteinemia for the prevention of coronary artery disease events. The Canadian Task Force on Preventive Health Care. CMAJ. 2000;163(1):21-29.

Bottiglieri T. Folate, vitamin B12, and neuropsychiatric disorders. Nutrition Rev. 1996;54(12):382-390.

Bottiglieri T, Laundy M, Crellin R, Toone BK, Carney MW, Reynolds EH. Homocysteine, folate, methylation, and monoamine metabolism in depression. J Neurol Neurosurg Psychiatry. 2000;69(2):228-232.

Boushey CJ, Beresford SA, Omenn GS, Motulsky AG. A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. JAMA. 1995;274:1049-1057.

Brattstrom LE, Hultberg BL, Hardebo JE. Folic acid responsive postmenopausal homocysteinemia. Metabolism. 1985;34(11):1073-1077.

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

Chatterjee S, Chowdhury RG, Khan B. Medical management of male infertility. J Indian Med Assoc. 2006 Feb;104(2):74, 76-7.

Choi SW. Vitamin B12 deficiency: a new risk factor for breast cancer? [Review]. Nutr Rev. 1999;57(8):250-253.

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.

Eikelboom JW, Lonn E, Genest J, Hankey G, Yusuf S. Homocyst(e)ine and cardiovascular disease: a critical review of the epidemiologic evidence. Ann Intern Med. 1999;131:363-375.

Fugh-Berman A, Cott JM. Dietary supplements and natural products as psychotherapeutic agents. Psychosom Med. 1999;61:712-728.

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.

Kaptan K, Beyan C, Ural AU, et al. Helicobacter pylori -- is it a novel causative agent in vitamin B12 deficiency? Arch Intern Med. 2000;160(9):1349-1353.

Konings EJ; Committee on Food Nutrition. Water-soluble vitamins. JAOAC Int. 2006 Jan-Feb;89(1):285-8.

Kris-Etherton P, Eckel RH, Howard BV, St. Jeor S, Bazzarre TL. Lyon diet heart study. Benefits of a Mediterranean-style, National Cholesterol Education Program/American Heart Association Step I dietary pattern on cardiovascular disease. Circulation. 2001;103:1823-1825.

Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J. Effective treatment of cobalamin deficiency with oral cobalamin. Blood. 1998;92(4):1191-1198.

Lederle FA. Oral cobalamin for pernicious anemia. Medicine's best kept secret? JAMA. 1991;265:94-95.

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

Louwman MW, van Dusseldorp M, van de Vijver FJ, et al. Signs of impaired cognitive function in adolescents with marginal cobalamin status. Am J Clin Nutr. 2000;72(3):762-769.

Malinow MR, Bostom AG, Krauss RM. Homocyst(e)ine, diet, and cardiovascular disease. A statement for healthcare professionals from the nutrition committee, American Heart Association. Circulation. 1999;99:178-182.

National Academy of Science. Recommended Daily Allowances. Accessed August 1, 2007.

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.

Schnyder G. Decreased rate of coronary restinosis after lowering of plasma homocysteine levels. N Engl J Med. 2001;345(22):1593-1600.

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

Sinclair S. Male infertility: nutritional and environmental considerations. Alt Med Rev. 2000;5(1):28-38.

Snowdon DA, Tully CL, Smith CD, Riley KR, Markesbery WR. Serum folate and the severity of atrophy of the neocortex in Alzheimer disease: findings from the Nun Study. Am J Clin Nutr. 2000;71:993-998.

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.

Verhaeverbeke I, Mets T, Mulkens K, Vandewoude M. Normalization of low vitamin B12 serum levels in older people by oral treatment. J Am Geriatr Soc. 1997;45:124-125.

Wang HX. Vitamin B12 and folate in relation to the development of Alzheimer's disease. Neurology. 2001;56:1188-1194.

Weir DG, Scott JM. Vitamin B12 "cobalamin." In: Shils, ME, Olson JA, Shike M, Ross AC, eds. Modern Nutrition in Health and Disease. 9th ed. Baltimore, MD: Williams & Wilkins; 1999:447-458.

Wu K, Helzlsouer KJ, Comstock GW, Hoffman SC, Nadeau MR, Selhub J. A prospective study on folate, B12, and pyridoxal 5'-phosphate (B6) and breast cancer.Cancer Epidemiol Biomarkers Prev. 1999;8(3):209-217.

Yoshihara K, Kubo C. Overview of medical treatment and management of chronic fatigue syndrome. Nippon Rinsho. 2007 Jun;65(6):1077-81. Review.

Young SN. The use of diet and dietary components in the study of factors controlling affect in humans: a review. J Psychiatr Neurosci. 1993;18(5):235-244.