Vitamin B12

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Vitamins

Article Vitamin B12, NMJ, [2], 2011 November

Vitamin B12, or Cobalamin is a water-soluble micronutrient. It was discovered to be the vitamin, that when administered, treated pernicious anemia. Vitamin B12 works along with other vitamins such as folic acid in the synthesis of DNA, red blood cells, and the myelin sheath which surrounds nerves and helps with nerve conduction. As a methyl donator, B12 plays an important role in homocysteine metabolism and is important for proper energy metabolism, immune function and nerve function.

Food Sources

The following foods have the highest concentration of vitamin B12. For a more expansive list on food sources of specific nutrients visit Health Canada's Dietary Reference Intakes for Vitamins or USDA's National Nutrient Database

Other food sources include:[1]

  • protein sources: Beef liver, kidney, clams, fish, poultry
  • dairy: eggs, milk
  • Other sources include: Some breakfast cereals, nutritional yeasts and other food products that are fortified with vitamin B12.

Significant amounts of vitamin B12 are only found in animal sources. Strict vegetarians and vegans are usually advised to supplement with the vitamin in order to obtain adequate amounts.


TThe following are the primary uses of Vitamin B12. [2] [3]

  • AIDS: Progression of the disease increases as well as neurological symptoms as serum levels of cobalamin decrease. This decrease could be result of decreased absorption, decreased intake, or due to the antagonistic effect of AZT drugs. The low levels of B12 may also be indicative of an overall nutritional deficiency. . Vitamin B12 has been shown to inhibit HIV replication in vitro and may be beneficial for individuals with AIDS.
Article Vitamin B12, and Folate in the Treatment of Some Psychiatric Illnesses, J Orthomolecular Med; 2012; Vol27(3)
  • Psychiatric Disorders: People with mental symptoms may also benefit by having CSF levels of B12 checked because they may be low despite normal serum levels. Regular injections of hydroxocobalamine is probably the best way to achieve adequate CSF levels.
  • Alzheimer's Disease and impaired mental function in the elderly: Vitamin B12 and folic acid are the two most common nutritional deficiencies found in the elderly. Even without other signs of deficiency or anemia, if these vitamins are low, they can lead to mental disturbances.
  • Depression: A deficiency in B12 can cause depression as it is essential for methylation of a compound in the brain called BH4 which is important for the synthesis of serotonin and dopamine. Supplementation can improve mood by aiding in proper synthesis of these neurotransmitters.
Article Vitamin B12 Metabolic Concerns, Vital Link; 2006 Winter
  • Diabetic Neuropathy: The mechanism by which supplementation of B12 helps with [Peripheral Neuropathy|diabetic neuropathy]] is not clear. It could be correcting a derangement in B12 metabolism seen in diabetics or treating an underlying deficiency. Injectable methylcobalamin seems to be the form of administration of choice.
  • Low Sperm Counts: B12 is essential in cellular replication and therefore a deficiency can lead to low sperm counts and decreased motility.
  • Multiple Sclerosis: A deficiency in B12 and errors in metabolism of the vitamin are well-known contributors to demyelination of nerves. If B12 deficiency co-exists with the disease, it may aggravate the symptoms and promote further progression. It has been found that some individuals with MS have derangements in B12 transport into cells rendering it inactive. Supplementation of methylcobalamin appears to be the form of choice for multiple sclerosis. It appears to help with afferent pathways or sensory symptoms but not efferent pathways or motor symptoms.
  • Tinnitus: Deficiency of B12 can lead to neuropathologies. It was found that many individuals with tinnitus and noise-induced hearing loss have a deficiency in the vitamin. There appears to be an association between auditory dysfunction and B12 deficiency and supplementation shows some improvement.
  • Breast Cancer: Deficiency in vitamin B12 can cause defects in proper DNA synthesis and DNA integrity which can promote the development of breast cancer.
  • Chronic Fatigue Syndrome: B12 deficiency can cause red blood cells to stay enlarged due to improper synthesis. This makes it difficult for them to move through capillaries and oxygenate tissues leading to chronic conditions including chronic fatigue syndrome. Hydroxocobalamine appears to be the form of choice.

Deficiency Symptoms

Vitamin B12 is unique to the water-soluble vitamins in that it is stored in the liver and therefore signs of deficiency may not present themselves until 5-6 years after poor dietary intake or issues with absorption.

  • Pernicious Anemia: is the classic sign of deficiency, however, a deficiency usually affects the brain and nervous system first.
  • Impaired Nerve Function: numbness, pins-and-needles sensations, or a burning feeling, impaired mental function (may mimic Alzheimer's disease)
  • Other: smooth, beefy red tongue, diarrhea. Folic acid supplementation can actually mask these B12 deficiency symptoms.

Excess Symptoms

Vitamin B12 is non-toxic. Rarely one might see a worsening of acne symptoms (acneiform exanthema) but this can resolve after a week of discontinuation of supplementation.

Assessment Procedure

Common Deficiency Tests [4]

  • Urine Methylamalonate - a high level indicates a deficiency
  • Serum Vitamin B12 - a low level indicates a deficiency
  • RBC Folate - a high level may indicate that Vitamin B12 is being blocked

Prescribing Considerations

There are several forms of vitamin B12 available.

  • Cyanocobalamin is the most common. Cyanocobalamin can be converted to either active form in the body.
  • Methylcobalamin and adenosylcobalamin are the only active forms, methylcobalamin is the main form available commercially in tablet form in the U.S.
  • Cobalamin can be administered orally or via injection. Even in the absence of intrinsic factor, oral cobalamin can increase serum vitamin B12 levels and is therapeutically effective in the treatment of [anemia|pernicious anemia]].[2]
  • Intrinsic factor is a digestive secretion that is essential for the absorption of vitamin B12.
  • The recommended dosages varies based on age and health status. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
  • Infants: 0.3mg (under 6 months); 0.5mg (6-12 months)
  • Child: 0.7mg (1-3 years); 1.0mg (4-6 years); 1.4mg (7-10 years)
  • Adolescent and Adult (11+ years): 2.0mg
  • Pregnancy: 2.2mg
  • Lactation: 2.1mg


  • Children: Supplementation may be important for children on a vegetarian or vegan diet. No significant safety issues have been demonstrated.
  • Pregnancy and Breastfeeding: No significant safety issues have been demonstrated.

Drug Interactions

  • Drug Interactions include:[5]
Supportive or Beneficial:
  • Antidepressants - Low B12 is associated with increased susceptibility to depression. Healthy B12 levels may enhance response to drug therapy and help with the biosynthesis of serotonin and dopamine. Some antidepressants deplete and/or antagonize B12.
  • Fibrates - B12 supplementation (along with folic acid and vitamin B6) may benefit by lowering elevated homocysteine levels seen with fenofibrate and bezafibrate. Fibrates may also impair B12 absorption.
  • Pemetrexed - Folic Acid and B12 can reduce homocysteine, enhance drug safety profile, and reduce drug toxicity without reduces efficacy of the drug.
Addresses Drug-Induced Deficiency:
  • Aminoglycoside Antibiotics - Drug decreases B12 absorption and biosynthesis, interferes with B12 metabolism and increases elimination. Methylcobalamin can reduce drug-induced ototoxicity.
  • Anticonvulsant Medications, Including Phenobarbital, Phenytoin, and Valproic Acid - Drug may decrease B12 absorption and can also lead to a foliate deficiency.
  • Bile Acid Sequestrants - Drug may reduce absorption of B12 and many other nutrients. Separate intake.
  • Chloramphenicol - Drug may reduce absorption of B12 and can oppose erythropoietic activity of B12 (or iron). Also co-administration (along with vitamin B6) may reduce or reverse adverse effects associated with the drug including optic neuritis.
  • Colchicine - Drug may interfere with B12 absorption and interfere with metabolism. Separate intake.
  • Histamine (H2) Receptor Antagonists - Drug decreases secretion intrinsic factor and thus impairs absorption of dietary B12.
  • Metformin and Related Biguanides - Drug reduces B12 absorption and lowers serum levels of B12 and holotranscobalamin by depressing intrinsic factor secretion.
  • Methotrexate - Drug interferes with folate metabolism and increases risk of B12 deficiency leading to risk of elevated homocysteine. Supplement with B12. Folic Acid can be supplemented with rheumatoid arthritis and psoriasis but avoid with cancer.
  • Nitrous Oxide - Chronic exposure to nitrous oxide may lead to B12 deficiency, decreased folate activity and possibly elevate homocysteine.
  • Oral Contraceptives - Decreased levels of B12 are associated with use of oral contraceptives.
  • Para-Aminosalicyclic Acid - Although only prescribed rarely, it would be prudent to co-adminster B12 as the drug is known to cause B12 malabsorption and depletion.
  • Proton Pump Inhibitors - Drug can impair absorption of dietary B12.
  • Zidovudine (AZT) and Related Antiretroviral Agents, Reverse-Transcriptase Inhibitor (Nucleoside) - B12 deficiency is common in individuals with HIV/AIDS and the drugs used to treat it can exacerbate the problem. Consider concomitant use of B12 and folate.

Nutrient Interactions

  • Nutrient Interactions include:[5]
  • Alcohol - Excessive alcohol intake can reduce absorption of B12.
  • Calcium - Increased intake of calcium can reverse vitamin B12 malabsorption induced by metformin.
  • Folic Acid - B12, folic acid, and vitamin B6 work together in many physiological processes including controlling homocysteine levels. Supplementation with folate might mask a deficiency in B12.
  • Potassium Chloride, sustained/controlled-release medications - Potassium can alter the amount of acid in the stomach and can therefore inhibit absorption of B12. Separate intake.
  • Vitamin B6 - see Folic Acid
  • Vitamin C - May potentially damage or diminish the effectiveness of B12. Do not take large doses of vitamin C within 1 hour of oral B12.
  • Vitamin D - May act synergistically together to reduce the risk of hip fractures in stroke patients with homocysteine as a predictive factor.


  1. Medlineplus [1]
  2. 2.0 2.1 Murray Michael T (2005) Encyclopedia of Nutritional Supplements, The Essential Guide for Improving Your Health Naturally Prima Publishing
  3. Hoffer Abram, Prousky Jonathan (2006) Naturopathic Nutrition, A Guide to Nutrient-Rich Food & Nutritional Supplements for Optimum Health CCNM Press
  4. Bralley J Alexander and Lord Richard S (2005) Laboratory Evaluations in Molecular Medicine, Nutrients, Toxicants, and Cell Regulators Institute for Advances in Molecular Medince, GA
  5. 5.0 5.1 Stargrove Mitchell Bebell, Treasure Jonathan, McKee Dwight L (2008) Herb, Nutrient, and Drug Interactions, Clinical Implications and Therapeutic Strategies. Mosby