Also indexed as: Adenosylcobalamin, Cobalamin, Cyanocobalamin,
Hydroxocobalamin, Hydroxycyanocobalamin, Methylcobalamin
Where is it found?
Vitamin B12 is found in all foods of animal origin, including dairy,
eggs, meat, poultry, and fish. According to one report, small, inconsistent
amounts occur in seaweed (including nori and chlorella) and tempeh.1 Many researchers and healthcare
professionals believe that people cannot rely on
vegetarian sources to provide predictably sufficient quantities of vitamin B12. However,
another study found substantial amounts of vitamin B12 in nori (at least 55 mcg per 100 grams
of dry weight).2
Vitamin B12 has been used
in connection with the following conditions (refer to the individual
health concern for complete information):
Who is likely to be deficient?
Vegans (vegetarians who also avoid dairy and
eggs) frequently become deficient, though the process often takes many years. People with
malabsorption conditions, including those with
tapeworm infestation and those with bacterial overgrowth in the intestines, often suffer from
vitamin B12 deficiency. Malabsorption of vitamin B12 can also result from pancreatic disease,
the effects of gastrointestinal surgery, or various prescription drugs.3
Pernicious anemia is a special form of
vitamin B12 malabsorption due to impaired ability of certain cells in the stomach to make
intrinsic factor—a substance needed for normal absorption of vitamin B12. By definition,
all people with pernicious anemia are vitamin B12-deficient. They require either vitamin B12
injections or oral supplementation with very high levels (1000 mcg per day) of vitamin
Older people with urinary incontinence4 and hearing loss5 have been
reported to be at increased risk of B12 deficiency.
Infection with Helicobacter
pylori, a common cause of gastritis and
ulcers, has been shown to cause or contribute
to adult vitamin B12 deficiency. H. pylori has this effect by damaging cells in the
stomach that make intrinsic factor—a substance needed for normal absorption of vitamin
B12. In one trial, H. pylori was detected in 56% of people with anemia due to vitamin
B12 deficiency. Successful eradication of H. pylori led to improved blood levels of
B12 in 40% of those infected.6 Other studies have also suggested a link between
H. pylori infection and vitamin B12 deficiency.7 8 Elimination
of H. pylori infection does not always improve vitamin B12 status. People with H.
pylori infections should have vitamin B12 status monitored.
In a preliminary report, 47% of people with
tinnitus and related disorders were found to have vitamin B12 deficiencies that may be
helped by supplementation.9
HIV-infected patients often have low blood
levels of vitamin B12.10
A disproportionate amount of people with psychiatric disorders are deficient in
B12.11 Significant vitamin B12 deficiency is associated with a doubled risk of
severe depression, according to a study of
physically disabled older women.12
A preliminary study found that
postmenopausal women who were in the lowest one-fifth of vitamin B12 consumption had an
increased risk of developing breast
Although blood levels of vitamin B12 may be higher in alcoholics, actual body stores of vitamin B12 in the
tissues (e.g., the liver) of alcoholics is frequently deficient.14
Low blood levels of vitamin B12 are sometimes seen in pregnant women; however, this does not always indicate
a vitamin B12 deficiency.16 The help of a healthcare professional is needed to
determine when a true vitamin B12 deficiency exists in pregnant women with low blood levels of
Hydroxocobalamin (a form of vitamin B12) has been recognized for more than 40 years as an
effective antidote to cyanide poisoning. It is currently being used in France for that
purpose. Because of its safety, hydroxocobalamin is considered by some researchers to be an
ideal treatment for cyanide poisoning.17
How much is usually taken?
Most people do not require vitamin B12 supplements. However, vegans should supplement with at least 2 to 3 mcg per
People with pernicious anemia are often
treated with injections of vitamin B12. However, oral administration of 1,000 mcg per day can
be used reliably as an alternative to vitamin B12 injections.18 19
20 21 22
Absorption of vitamin B12 is reduced with increasing age. Some research suggests that
elderly people may benefit from 10 to 25 mcg per day of vitamin B12.23
24 25 One study of elderly people with vitamin B12 deficiency suggested that
as much as 500 to 1,000 mcg of vitamin B12 per day might be necessary to achieve optimal
vitamin B12 status.26 Vitamin B12 status was measured in this study using a
sensitive laboratory test (the plasma methylmalonic acid concentration).
When vitamin B12 is used for therapeutic purposes other than correcting a
deficiency, injections are usually necessary to achieve results.
Sublingual forms of vitamin B12 are available,27 but there is no proof that they
offer any advantage to oral supplements.
Are there any side effects or interactions?
Oral vitamin B12 supplements are not generally associated with any side effects.
Although quite rare, serious allergic
reactions to injections of vitamin B12 (sometimes even life-threatening) have
been reported.28 29 Whether these reactions are to the vitamin itself,
or to preservatives or other substances in the injectable vitamin B12 solution, remains
somewhat unclear. Most, but not all, injectable vitamin B12 contains preservatives.
If a person is deficient in vitamin B12 and takes 1,000 mcg or more of folic acid per day, the folic acid supplementation can
improve the anemia caused by vitamin B12
deficiency. The effect of folic acid on vitamin B12 deficiency-induced anemia is not a
folic acid toxicity. Rather, the folic acid supplementation is acting to correct one of the
problems caused by B12 deficiency. The other problems caused by a lack of vitamin B12 (mostly
neurological) do not improve with folic acid supplements, and can become irreversible
if vitamin B12 is not provided to someone who is vitamin B12 deficient.
Some doctors are unaware that vitamin B12 deficiencies often occur without
anemia—even in people who do not take folic acid supplements. This lack of knowledge can
delay diagnosis and treatment of people with vitamin B12 deficiencies. This can lead to
permanent injury. When such a delayed diagnosis occurs in someone who inadvertently erased the
anemia of vitamin B12 deficiency by taking folic acid supplements, the folic acid
supplementation is often blamed for the missed diagnosis. This problem is rare and should not
occur in people whose doctors understand that a lack of anemia does not rule out a vitamin B12
deficiency. Anyone supplementing 1,000 mcg or more per day of folic acid should be initially
evaluated by a doctor before the folic acid can obscure a proper diagnosis of a possible B12
Are there any drug
Certain medicines may interact with vitamin B12. Refer to drug interactions for a list of those medicines.
1. Rauma AL, Torronsen R, Hanninen O, Mykkanen H. Vitamin B12 status of
long term adherents of a strict uncooked vegan diet (“living food diet”) is
compromised. J Nutr 1995;125:2511–5.
2. Takenaka S, Sugiyama S, Ebara S, et al. Feeding dried purple laver
(nori) to vitamin B12-deficient rats significantly improves vitamin B12 status. Br J
3. Snow CF. Laboratory diagnosis of vitamin B12 and folate deficiency. A
guide for the primary care physician. Arch Intern Med 1999;159:1289–98
4. Rana S, D’Amico F, Merenstein JH. Relationship of vitamin B12
deficiency with incontinence in older people. J Am Geriatr Soc 1998;46:931
5. Houston DK, Johnson MA, Nozza RJ, et al. Age-related hearing loss,
vitamin B-12, and folate in elderly women. Am J Clin Nutr 1999;69:564–71.
6. Kaptan K, Beyan C, Ural AU, et al. Helicobacter pylori—is it a
novel causative agent in Vitamin B12 deficiency? Arch Intern Med
7. Perez-Perez GI. Role of Helicobacter pylori infection in the
development of pernicious anemia. Clin Infect Dis 1997;25:1020–2 [review].
8. Fong TL, Dooley CP, Dehesa M, et al. Helicobacter pylori infection in
pernicious anemia: a prospective controlled study. Gastroenterology
9. Shemesh Z, Attias J, Ornan M, et al. Vitamin B12 deficiency in
patients with chronic-tinnitus and noise-induced hearing loss. Am J Otolaryngol
10. Remacha AF, Cadafalch J. Cobalamin deficiency in patients infected
with the human immunodeficiency virus. Semin Hematol 1999;36:75–87.
11. Lindenbaum J, Healton EB, Savage DG, et al. Neuropsychiatric
disorders caused by cobalamin deficiency in the absence of anemia or macrocytosis. N Engl
J Med 1988;318:1720–8.
12. Penninx BW, Guralnik JM, Ferrucci L, et al. Vitamin B(12) deficiency
and depression in physically disabled older women: epidemiologic evidence from the
Women’s Health and Aging Study. Am J Psychiatry 2000;157:715–21.
13. Wu K, Helzlsouer KJ, Comstock GW, et al. A prospective study on
folate, B12, and pyridoxal 5’-phosphate (B6) and breast cancer. Cancer Epidemiol
Biomarkers Prev 1999;8:209–17.
14. Kanazawa S, Herbert V. Total corrinoid, cobalamin (vitamin B12), and
cobalamin analogue levels may be normal in serum despite cobalamin in liver depletion in
patients with alcoholism. Lab Invest 1985;53:108–10.
15. Cravo ML, Camilo ME. Hyperhomocysteinemia in chronic alcoholism:
relations to folic acid and vitamins B(6) and B(12) status. Nutrition
16. Pardo J, Peled Y, Bar J, et al. Evaluation of low serum vitamin B(12)
in the non-anaemic pregnant patient. Hum Reprod 2000;15:224–6.
17. Sauer SW, Keim ME. Hydroxocobalamin: improved public health readiness
for cyanide disasters. Ann Emerg Med 2001;37:635–41.
18. Goldberg TH. Oral vitamin B12 supplementation for elderly patients
with B12 deficiency. J Am Geriatr Soc 1995;43:SA73 [abstr #P258].
19. Lederle FA. Oral cobalamin for pernicious
anemia—medicine’s best kept secret? JAMA 1991;265:94–5
20. Kondo H. Haematological effects of oral cobalamin preparations on
patients with megaloblastic anemia. Acta Haematol 1998;99:200–5.
21. Waif SO, Jansen CJ, Crabtree RE, et al. Oral vitamin B12 without
intrinsic factor in the treatment of pernicious anemia. Ann Intern Med
22. Crosby WH. Oral cyanocobalamin without intrinsic factor for
pernicious anemia. Arch Intern Med 1980;140:1582.
23. Kaufman W. The use of vitamin therapy to reverse certain concomitants
of aging. J Am Geriatr Soc 1955;3:927–36.
24. Lindenbaum J, Rosenberg IH, Wilson PWF, et al. Prevalence of
cobalamin deficiency in the Framingham elderly population. Am J Clin Nutr
25. Verhaeverbeke I, Mets T, Mulkens K, Vandewoulde M. Normalization of
low vitamin B12 serum levels in older people by oral treatment. J Am Geriatr Soc
26. Eussen SJ, de Groot LC, Clarke R, et al. Oral cyanocobalamin
supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch
Intern Med 2005;165:1167–72.
27. Delpre G, Stark P, Niv Y. Sublingual therapy for cobalamin deficiency
as an alternative to oral and parenteral cobalamin supplementation. Lancet
28. Snowden JA, Chan-Lam D, Thomas SE, Ng JP. Oral or parenteral therapy
for vitamin B12 deficiency. Lancet 1999;353:411 [letter].
29. Hovding G. Anaphylactic reaction after injection of vitamin B12.
Br Med J 1968;3:102.