vitamin B12

What Is It?
Health Benefits

Recommended Intake
If You Get Too Little

If You Get Too Much

General Dosage Information

Guidelines for Use

General Interaction

Evidence Based Rating Scale


What Is It?

In l948, scientists successfully identified a nutritional substance in calf's liver that could prevent pernicious anemia, a potentially deadly disorder that mainly affects older adults. The compound—Vitamin Bl2 (or cobalamin)—turned out to be the last vitamin to be discovered.

Vitamin B12 is the only one of the B vitamins that the body stores in substantial amounts. Except for people who don't eat any animal products (vegans), most people get adequate amounts of B12 in their diets; however, for the body to absorb the vitamin, it has to be separated from the Protein in food, a complicated process. An individual must be able to produce enough digestive enzymes and stomach acid for this separation to take place. The vitamin then bonds with intrinsic factor (a substance secreted by cells in the stomach lining) and is transported to the small intestine, where it is absorbed. Some individuals are unable to make sufficient quantities of intrinsic factor or stomach acid as they age, a situation ripe for a deficiency to develop. Experts estimate that as many as 20% of older adults are deficient in vitamin B12 but don’t know it. Other groups at particular risk for a deficiency are those who have had a portion of the stomach removed, e.g. for bariatric surgery, resulting in inadequate intrinsic factor secreting cells; those with ulcers, Crohn's disease or other gastrointestinal disorders; and those taking medications for epilepsy, chronic heartburn, or gout, which can interfere with B12 absorption. Nitrous oxide used for anesthesia—often in dental offices as well as hospitals—can cause rapid development of symptoms in people who are already deficient. Heavy drinkers are also likely to have low levels of B12 because excessive alcohol consumption hinders the nutrient's absorption. And rare in the U.S., a form of tapeworm, Diphyllobothrium latum, found in some South American fish, can deplete B12 levels. Deficiency can cause fatigue, glossitis (tongue inflammation), depression, confusion, memory loss, muscle weakness, and numbness and tingling in the hands and feet due to nerve damage.

Health Benefits

Not only does vitamin B12 help in the formation of healthy red blood cells, it is also involved in the maintenance of the myelin sheath, the fatty substance that covers nerves and enables them to function properly. Additionally, the body needs this vitamin for cell replication, for proper energy metabolism and to create the genetic material in cells known as DNA and RNA.

Vitamin B12 is of potential value in treating the effects of aging and Alzheimer's disease, as well as depression, the skin disorder known as rosacea, tinnitus (ringing in the ears), and various neurologic problems. It may also aid in preventing heart disease and boost the immune system.

Specifically, vitamin B12 may help to:

Correct pernicious anemia and vitamin B12 deficiency. Anemia—a shortage of the red blood cells that carry oxygen through the body—can be caused by both excess blood loss and by inadequate building blocks needed to form the red blood cells. The form known as pernicious anemia results from a deficiency of vitamin B12 either from inadequate intake or inadequate amounts of the stomach enzymes, acids, and intrinsic factor needed for absorption and transport. In anemia from whatever cause, a lack of oxygen in the blood results in weakness and fatigue. In the case of pernicious anemia, the B12 deficiency may also cause damage to the nerves and result in pain and/or tingling or numbness in fingers or toes. Taking vitamin B12 can help to restore levels and remedy anemia due to a deficiency. It’s usually given with folic acid because high levels of one of these nutrients can conceal a deficiency of the other. These nutrients work together to increase the formation of red blood cells, thereby correcting anemia and increasing oxygen carrying capacity in the blood supply. Formerly, it was believed that only injectable forms of B12 were effective; however more recent studies indicate efficacy of several forms of B12, including injections, nasal spray and oral supplements: a large dosage of oral vitamin B12 (between 600 to 2,000 mcg daily) appears to be as effective as intramuscular injections. (1-8) A 2009 review of studies cited four prospective studies in well-determined populations, three prospective randomized studies and a systematic review by the Cochrane group as evidence that at least 1,000 mcg of oral vitamin  B12  daily may adequately treat pernicious anemia. (6)

Older adults with vitamin B12 deficiency due to lack of intrinsic factor and malabsorption also can benefit from taking oral supplements. A 2002 Canadian study of 242 active and otherwise healthy older adults found those taking 25 to 37.5 mcg vitamin B12 daily were more likely to have normal vitamin B12 levels than those who did not take supplements. (7) However, another study found these older adults may need to take 50 to 100 mcg vitamin B12 daily may be needed to restore levels to normal in those who are deficient. (8)

Prevent and treat Alzheimer’s disease. Although not the cause of Alzheimer’s disease, low levels of B vitamins have occasionally been found in patients who have this degenerative disorder of the brain. Taking vitamin B12, theoretically, may help to prevent the development of the disease by lowering blood levels of homocysteine, an amino acid that is believed to contribute to impaired cognitive function after extended periods of elevated levels. However, preliminary evidence in this area has not been promising. A two-year, double-blind, placebo-controlled, randomized trial beginning in 2006 in New Zealand evaluated 276 healthy participants over 65 with elevated homocysteine levels. The treatment group received supplements of folate (1,000 mg), vitamin B12 (500 mcg) and vitamin B6 (10 mg) daily resulting in significantly lower homocysteine levels than the control group. No significant differences were noted between the vitamin and placebo groups in test scores of cognition; however the duration of the study may have been too short to detect such changes in a healthy population. (9) Several further studies examined the relationship of high homocysteine levels to Alzheimer's disease and found that high levels of the amino acid, as well as deficiencies in folate and the B vitamins, seem to predate dementia rather than occur as a result of the disease. (10-12) And, later studies found that while increasing folate intake may decrease the risk of developing Alzheimer’s disease, the same is not true for vitamin B6 and vitamin B12 supplementation. (13-15)

However, preliminary studies indicate potential efficacy in treating mild to moderate Alzheimer’s disease. In a 2009 placebo-controlled pilot study, 12 institutionalized patients with moderate or more severe Alzheimer’s disease received a vitamin formula containing either vitamin B12 or placebo. Patients in the treatment group showed a clinically significant delay in decline on the Dementia Rating Scale compared to the placebo group, and caregivers reported a 30 percent improvement in the treatment group in cognitive function, daily function and memory for more than nine months. Larger trials are needed to confirm or refute these initial findings. (16) 

Improve symptoms of chronic fatigue syndrome. Chronic fatigue syndrome, a disorder characterized by unexplained exhaustion, can be associated with deficiencies in vitamins such as vitamin B12. Preliminary evidence indicates that vitamin B12 supplementation may help to improve symptoms of chronic fatigue syndrome by correcting red blood cell abnormalities and improving oxygen delivery to tissues. One study indicated that receiving intramuscular injections of 5 mg of vitamin B12 twice a week may help to improve general well-being and happiness of patients complaining of tiredness or fatigue. (17, 18) More research is needed to confirm or refute efficacy in chronic fatigue syndrome.

Restore a deficiency due to Crohn’s disease. Crohn’s disease is a chronic inflammatory condition of the intestine, which can cause damage to the portion of the small intestine where vitamin B12 is absorbed and cause a deficiency of  the vitamin. Preliminary evidence indicates taking vitamin B12 supplementation may help to improve low levels caused by Crohn’s disease. (19)

Increase sperm count in infertile men. Vitamin B12 is necessary for the maturation of cells. Several studies have shown that raising levels of B12 has improved sperm counts in infertile men. (20-22) In a preliminary study in Japan, dosages of 1,500 mcg of the methylcobalamin form of B12 were administered daily to 26 infertile men for four to 24 weeks. After eight weeks, a semen analysis showed sperm concentration increased in 38% of the men, total sperm counts increased in 53%, sperm motility increased in 50%, and total motile sperm count increased in 50%. (21) A 2000 review of nutritional and environmental therapies indicated that vitamin B12 has been shown to improve sperm production and motility. (23)

Repair skin cells in patients with rosacea and eczema. People with skin conditions such as rosacea or eczema, characterized by redness of the face, hands, elbows, scalp and wrists, may be deficient in B vitamins. Taking a B complex encourages the secretion of protective mucus by skin cells and helps eliminate cellular waste, improving the appearance of the skin. Likewise, the extra vitamin B12 in a B complex is essential to the growth, repair, and replication of healthy skin cells. However, research in this area is lacking. In fact, some research indicates that large doses of vitamin B12 may actually cause rosacea rather than treat it. (24, 25) Preliminary research indicates that applying a specific topical vitamin B12 0.07% cream (Regividerm) twice daily reduces the extent and severity of eczema compared to placebo. (26)

Prevent or treat tinnitus. Vitamin B12 is essential in the manufacture of myelin, a fatty substance that covers and shields the nerves and allows them to function properly. Tinnitus, or ringing in the ears, is a common problem that can be annoying even though there are no severe consequences. The cause of tinnitus is unknown, but for some sufferers, the problem is attributed to damage to the nerves of the inner ear resulting from frequent exposure to loud noises such as rock music, machinery, jet engines, gunshots or explosives. In a group of military personnel, B12 deficiency was significantly more common in those with tinnitus plus noise-induced hearing lost than in those with hearing loss alone or in normals. (27) Thus, vitamin B12 supplementation may help to protect these nerves; however, research is lacking in this area.

Treat diabetic neuropathy. In a randomized placebo-controlled double-blind study of 36 patients with diabetic neuropathy treated with 500 mg three times a day for four months, peripheral neurology scores, but not nerve conduction studies, improved significantly in the treated group. (28)

Improve depression. Some research has linked depression to imbalances in the brain’s production of neurotransmitters, chemicals that pass messages from one nerve cell to another. Taking a vitamin B complex may help to enhance neurotransmitter production and strengthen the nerves. In a group of 700 disabled women, over age 65, those with B12 deficiency were more than twice as likely to be depressed on a standardized depression scale. (29) Treatment studies are needed.

Osteoporosis. B12 deficiency seems to be related to osteoporotic bone loss and to hip and spine fractures (30). Supplementation with B12 and folate significantly reduced hip fractures in a group of 625 Japanese men and women following strokes. (31) It’s unclear whether similar benefit would be seen in other populations.  

Treat incontinence. In a case-control study with 104 matched pairs, those with B12 deficiency were two and a half times more likely to be incontinent. Treatment studies are needed. (32)




  • tablet
  • spray
  • liquid
  • cream
  • nasal gel 

Recommended Intake

The RDA for vitamin B12 for adults and children older than 13 is 2.4 mcg daily. In older adults 25mcg has been used for maintenance and, supplementation of 50- to 100 mcg daily has been used to restore B12 levels in patients with a deficiency.

If You Get Too Little

A deficiency can cause fatigue, depression, confusion, memory loss, muscle weakness, and numbness and tingling in the hands and feet due to nerve damage. A deficiency in adolescents aged 10 to 16 who have been fed a strict vegetarian diet from infancy to six years of age also has been associated with impaired cognitive performance.

If You Get Too Much

Because the vitamin seems to have a very low potential for toxicity and is water-soluble – what the body cannot use, it eliminates in the urine and feces within 12 hours – vitamin B12 seems to be safe even in very large doses. While a tolerable upper intake level (UL) has not been assigned to vitamin B12, there is insufficient reliable information to advocate exceeding the RDA for vitamin B12 other than in the elderly population, patients with evidence of deficiency, or patients at risk for deficiency because of other conditions and/or medication use.

General Dosage Information

  • For Alzheimer’s Disease: 500 to 1,000 mcg daily of oral vitamin B12.

  • For pernicious anemia: 1,000 mcg daily of oral vitamin B12 or intramuscular injections per your physician’s instruction.

  • For chronic fatigue syndrome: 1,000 mcg daily of oral vitamin B12.

  • For Crohn’s disease: 1,000 mcg daily of sublingually vitamin B12.

  • For depression: 1,000 mcg daily of sublingually vitamin B12.

  • For diabetes: 1,000 mcg daily of sublingually vitamin B12.

  • For eczema: 0.07% vitamin B12 cream (Regividerm) twice daily has been used.

  • For male infertility: 1,000 to 1,500 mcg oral methylcobalamin form of B12 twice weekly has been used.

  • For osteoporosis: 1,000 mcg daily of oral vitamin B12.

  • For tinnitus: 1,000 mcg sublingually daily has been used.

Guidelines for Use

Vitamin B12 is frequently used in combination with other B vitamins, such as in a vitamin B complex that also includes B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin/niacinamide), vitamin B5 (panthothenic acid), vitamin B6 (pyridoxine), and folic acid.

General Interaction

Potassium supplements and numerous drugs interfere with B12 absorption. In particular, chloramphenicol, a now rarely used antibiotic, interferes with the red blood cell response to B12.


Be sure to take a folic acid supplement along with vitamin B12. A high intake of one can mask a deficiency in the other.

Because vitamin B12 contains cobalt, people who are sensitive or allergic to cobalamin and cobalt should avoid taking vitamin B12 supplements.


1. Lederle FA. Oral cobalamin for pernicious anemia. Medicine’s best kept secret? JAMA. 1991;265:94-5.
2. Hathcock JN, Troendle GJ. Oral cobalamin for treatment of pernicious anemia? JAMA. 1991;265-97.
3. Elia M. Oral or parenteral therapy for B12 deficiency. Lancet. 1998;352:1721-2.
4. Kuzminski AM, Del Giacco EJ, et al. Effective treatment of cobalamin deficiency with oral cobalamin. Blood. 1998;92:1191-8.
5. Andres E, Goichot B, Schlienger JL. Food cobalamin malabsorption: a usual cause of vitamin B12 deficiency. Arch Intern Med. 2000;160:2061-2.
6. Andrés E, Dali-Youcef N, Vogel T, et al. Oral cobalamin (vitamin B(12)) treatment. An update. Int J Lab Hematol. 2009 Feb;31(1):1-8.
7. Garcia A, Pombo-Paris A, Evans L, et al. Is low-dose oral cobalamin enough to normalize cobalamin function in older people? J Am Geriatr Soc. 2002;50:1401-4.
8. Seal EC, Metz J, Flicker L, Melny J. A randomized, double-blind, placebo-controlled study of oral vitamin B12 supplementation in older patients with subnormal or borderline serum vitamin B12 concentrations. J Am Geriatr Soc. 2002;50:146-51.
9. McMahon JA, Green TJ, Skeaff CM, et al. A controlled trial of homocysteine lowering and cognitive performance. N Engl J Med. 2006 Jun 29;354(26):2764-72.
10. Annerbo S, Wahlund LO, Lökk J. The relation between homocysteine levels and development of Alzheimer’s disease in mild cognitive impairment patients. Dement Geriatr Cogn Disord. 2005;20(4):209-14.
11. Quadri P, Fragiacomo C, Pezzati R, et al. Homocysteine and B vitamins in mild cognitive impairment and dementia. Clin Chem Lab Med. 2005;43(10):1096-100.
12. Kado DM, Karlamangla AS, Huang MH, et al. Homocysteine versus the vitamins folate, B6 and B12 as predictors of cognitive function and decline in older high-functioning adults: MacArthur Studies of Successful Aging. Am J Med. 2005 Feb;118(2):161-7.
13. Ariogul S, Cankurtaran M, Dagli N, et al. Vitamin B12, folate, homocysteine and dementia: are they really related? Arch Gerontol Geriatr. 2005 Mar-Apr;40(2):139-46.
14. Luchsinger JA, Tang MX, Miller J, et al. Relation of higher folate intake to lower risk of Alzheimer disease in the elderly. Arch Neurol. 2007 Jan;64(1):86-92.
15. van Dyck CH, Lyness JM, Rohrbaugh RM, Siegal AP. Cognitive and psychiatric effects of vitamin B12 replacement in dementia with low serum B12 levels: a nursing home study. Int Psychogeriatr. 2009 Feb;21(1):138-47.
16. Remington R, Chan A, Paskavitz J, Shea TB. Efficacy of a vitamin/nutriceutical formulation for moderate-stage to later-stage Alzheimer’s disease: a placebo-controlled pilot study. Am J Alzheimers Dis Other Demen. 2009 Feb-Mar;24(1):27-33.
17. Ellis FR, Nasser S. A pilot study of vitamin B12 in the treatment of tiredness. Br J Nutr. 1973;30:277-83.
18. Werbach MR. Nutritional strategies for treating chronic fatigue syndrome. Altern Med Rev. 2000;5:93-108.
19. Loew D, Wanitschke R, Schroedter A. Studies on vitamin B12 status in the elderly – prophylactic and therapeutic consequences. Int J Vitam Nutr Res. 1999 May;69(3):228-33.
20. Furnass SB. Seminal vitamin B-12 and sterility. Lancet. 1963 Jan 5;1(7271):59-60.
21. Isoyama R, Kawai S, Shimizu Y, et al. [Clinical experience with methylcobalamin (CH3-B12) for male infertility.] Hinyokika Kiyo. 1984 Apr;30(4):581-6.
22. Moriyama H, Nakamura K, Sanda N, et al. [Studies on the usefulness of a long-term, high-dose treatment of methylcoalamin in patients with oligozoospermia.] Hinyokika Kiyo. 1987 jan;33(1):151-6.
23. Sinclair S. Male infertility: nutritional and environmental considerations. Altern Med Rev. 2000 Feb;5(1):28-38.
24. Sherertz EF. Acneiform eruption due to “megadose” vitamins B6 and B12. Cutis. 1991 Aug;48(2):119-20.
25. Jansen T, Romiti R, Kreuter A, Altmeyer P. Rosacea fulminans triggered by high-dose vitamins B6 and B12. J Eur Acad Dermatol Venereol. 2001 Sep;15(5):484-5.
26. Stucker M, Pieck C, Stoerb C, et al. Topical vitamin B12 – a new therapeutic approach in atopic dermatitis – evaluation of efficacy and tolerability in a randomized placebo-controlled multicentre clinical trial. Br J Dematol. 2004;150:977-83.
27. Shemesh A, Attias J, Ornan M et al. Vitamin B12 deficiency in patients with chronic tinnitus and noise-induced hearing loss. Am J Otolaryngol, 1993;14:94-99.
28. Yaqub BA, Siddique A, Sulimani R, Effects of methylcobalamin on diabetic neuropathy, Clin Neurol Neurosurg, 1992;94:105-111.
29. Penninx BWJH, Guralnik JH, Ferrucci L et al. Vitamin B12 deficiency and depression in physically disabled older women: epidemiologic evidence from the Women’s Health and Aging study. Am J Psychiatry, 2000;157:715-721.
30. Tucker KL; Hannan MT; Qiao N; Jacques PF; Selhub J; Cupples LA; Kiel DP, Low plasma vitamin B12 is associated with lower BMD: the Framingham Osteoporosis Study. J Bone Miner Res 2005 Jan;20(1):152-8. Epub 2004 Oct 25.
31. Sato Y; Honda Y; Iwamoto J; Kanoko T; Satoh K Effect of folate and mecobalamin on hip fractures in patients with stroke: a randomized controlled trial. JAMA 2005 Mar 2;293(9):1082-8.
32.Rana S, D’Amico F, Merenstein JH. Relationship of vitamin B12 deficiency with incontinence in older people. J Am Geriatr Soc, 1998;46:931-932. 

Evidence Based Rating Scale  

The Evidence Based Rating Scale is a tool that helps consumers translate the findings of medical research studies with what our clinical advisors have found to be efficacious in their personal practice. This tool is meant to simplify which supplements and therapies demonstrate promise in the treatment of certain conditions. This scale does not take into account any possible interactions with any medication/ condition/ or therapy which you may be currently undertaking. It is therefore advisable to ask your doctor before starting any new treatment regimen.


Date Published: 04/19/2005
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