For Patients & Caregivers
Vitamin B12, in combination with folate and vitamin B6, may reduce breast cancer risk.
Vitamin B12 is involved in synthesis of phospholipids, neurotransmitters, DNA, and the metabolism of fatty acids and amino acids in cells. It is found in meat, fish, dairy products, and fortified cereals. Drugs that reduce stomach acid secretion or production of intrinsic factor can reduce B12 absorption. Other drugs such as metformin or oral contraceptives may also decrease B12 absorption. High levels of folic acid intake may mask a B12 deficiency. Patients should discuss supplement use with their physicians.
- B12 deficiency
Diagnosed deficiencies can be effectively treated with B12 therapy if dietary changes alone are not enough.
- Pernicious anemia
The injectable form of B12 is used as prescription drug to treat pernicious anemia.
- Cardiovascular disease
When combined with folate and B6, vitamin B12 can reduce homocysteine levels, which may offer benefit for cardiovascular disorders.
- Breast cancer
Some studies show a reduction in breast cancer risk with vitamin B12 when used in combination with folate and B6.
- Cognitive function
Neither B12 supplementation alone or in combination with folic acid showed any improvement in cognitive function in a clinical study.
In those without a vitamin B12 deficiency, there is little indication in the medical literature that B12 supplementation can improve fatigue symptoms.
Two large-scales studies do not support this use.
- Lung cancer
Findings from one study suggest that B12 levels have no effect on the risk of lung cancer.
For Healthcare Professionals
Vitamin B12 is part of the vitamin B-complex family and refers to the group of compounds that consists of cyanocobalamin, hydroxycobalamin, and related substances (1). It is essential for normal nerve function, DNA synthesis, hematopoiesis, fatty acid metabolism, and amino acid synthesis in the mitochondria. It also plays an important role in the metabolism of homocysteine and synthesis of S-adenosylmethionine (SAMe), another compound that is essential to many biological processes.
Vitamin B12 is naturally synthesized by bacteria and abundant in diets that include meat and dairy products, although a deficiency can occur in those who have malabsorption syndromes (2), take medications for gastric disorders (3)(4) or for conditions associated with insulin resistance (5), or those who follow a strict vegetarian diet (6). B12 deficiency is also more common among the elderly (7). Lack of B12 can lead to a wide variety of hematologic, neurologic, and psychiatric disorders, and may increase the risk of cardiovascular diseases (8). Low serum B12 levels have been associated with increased bone turnover and fracture risk (9). Repletion of vitamin B12 may improve response in patients resistant to antidepressants (10).
When used as homocysteine-lowering therapy, vitamin B12, folate, and vitamin B6 may have some cardiovascular benefits after coronary interventions (11), but do not appear to reduce the risk of further cardiovascular events including stroke (12)(13)(14). In addition, increased risk of in-stent restenosis with such treatment has been reported in patients after coronary stenting (15), and B12 supplementation as part of homocysteine-lowering therapy does not improve cognitive function (16)(17)(18)(19).
Clinical studies show that increased intake of vitamin B12 together with folate and vitamin B6 may lower the risk of breast (20)(21)(22) and cervical cancers (23), but has no effect on the risk of lung cancer (24). Findings from another study indicate that a combination of folate and vitamins B6 and B12 did not have an effect on overall risk of invasive cancer or breast cancer (25). However, data from a Norwegian study suggest higher cancer incidence and mortality in patients with ischemic heart disease following supplementation with vitamin B12 and folic acid (26). Further studies are needed to confirm these findings in other populations.
Supplementation with vitamin B12 intramuscular injections and oral folic acid reduces toxicity of pemetrexed chemotherapy in patients with non-small cell lung cancer (27), and may also help to improve treatment efficacy (28)(29).
Vitamin B12 is involved in the transfer of methyl groups and methylation reactions essential for the synthesis of phospholipids and neurotransmitters in the central nervous system. B12 is also required for synthesis of nucleic acid, notably DNA, the metabolism of fatty acids and amino acids in the mitochondria, and in delivering SAMe, the universal methyl donor (16)(30). In humans, two enzymatic reactions dependent on B12 are produced and activated in two separate cellular compartments: methylcobalamin in the cytosol and adenosylcobalamin in the mitochondria (1). As a coenzyme in methyl transfer reactions, it converts homocysteine to methionine, and it also participates in L-methylmalonyl-coenzyme A (CoA) conversion to succinyl-CoA (8). In the first enzyme reaction, methylcobalamin is used to recycle the folate cofactor 5-methyltetrahydrofolate to tetrahydrofolate thereby allowing the folate cofactor to participate in a cycle involving the biosynthesis of purines and pyrimidines. During this reaction, homocysteine is converted to methionine yielding the methyl groups required for methylation that is essential in biosynthesis (31).
When used with pemetrexed, B12/folic acid therapy further increases sub-G1 populations in human adenocarcinoma and large-cell carcinoma cell lines, independent of p53 status (28).
Proton pump inhibitors or histamine type 2 (H2)-receptor antagonists: Medications to treat gastric disorders that interfere with or suppress gastric acid and intrinsic factor production can lead to a decrease in vitamin B12 absorption (3)(4).
Biguanides (metformin): Medications used to treat type 2 diabetes, metabolic syndrome, nonalcoholic fatty liver disease, and polycystic ovary syndrome can lead to decreased vitamin B12 absorption (5).
Folic acid: Ingesting amounts greater than the Tolerable Upper Intake Level may mask vitamin B12 deficiency symptoms (33).
Oral contraceptives: May lower serum vitamin B12 concentrations (34).