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Vitamin B₁₂ is a water-soluble B complex vitamin obtained primarily from animal sources. It is also known as cobalamin, because it is a cobalt-containing compound. The body needs only tiny amounts of B₁₂ and stores it better than the other B vitamins, but lack of B₁₂ in the diet or an inability to absorb it can eventually cause nervous system problems, pernicious anemia, and other ailments.

Why is it essential? Vitamin B₁₂ aids in energy production from fats and carbohydrates and in the production of amino acid. Nerves need B₁₂ to maintain healthy myelin sheaths. The vitamin is also involved in production of the mood-affecting substance S-adenosyl methionine. Vitamin B₁₂ works with folic acid to control blood levels of the amino acid homocysteine. It aids in the formation of red blood cells, the nucleic acids DNA and RNA, and other vitamins. Pregnant women and children need adequate B₁₂ for normal growth and development. B₁₂ assists immune function and melatonin secretion.

Benefits and uses: An excess of homocysteine (which B₁₂ can help prevent) dramatically increases the risk of heart disease and perhaps osteoporosis. Many people find that B₁₂ increases their bodily energy and prevents fatigue. Inadequate body levels have been tied to hearing problems—one study of B₁₂ levels in soldiers, 50 percent of whom suffered from either tinnitus or hearing loss, found that nearly half of the soldiers with hearing problems were deficient in B₁₂, fewer than one in five of the soldiers with normal hearing had deficiencies, and tinnitus was most severe among those soldiers with the lowest B₁₂ levels. Vitamin B₁₂ may reduce the rate of various emotional and nervous system disorders, including depression, age-related mental impairment, and multiple sclerosis. Vitamin B₁₂ may also help prevent or treat asthma, bursitis, diabetes, hepatitis, male infertility, retinopathy, shingles, and bursitis.

Daily requirement: The NRC recently increased slightly the recommended dietary intake for B₁₂. The adult RDI is 2.4 to 2.8 mcg.

Deficiency risk factors: After several years, vegans (vegetarians who also avoid dairy and eggs) face some risk of long-term deficiency. Many people who suffer from a vitamin B₁₂ deficiency have a malabsorption condition, often related to lack of a stomach enzyme (intrinsic factor) needed for the small intestines to absorb B₁₂. Malabsorption is very common among the elderly, mainly due to an autoimmune-induced atrophy of the mucous membrane that lines the stomach. People with diabetes or thyroid disorders are also at increased risk for a B₁₂ deficiency. Stress, alcoholism, and overuse of antacids can increase the need for B₁₂. Deficiencies in B₁₂ may cause neurological problems, numbness in the hands and feet, diarrhea, confusion, fatigue, depression, and memory loss.

Optimal intake: An optimal daily supplement level of B₁₂ is 50 to 150 mcg. Larger doses (such as 1,000 to 2,000 mcg per day) are used to reverse pernicious anemia.

Food sources: Vitamin B₁₂ occurs principally in animal products, as it is stored in tissues after being produced by the action of certain bacteria in the intestines. Rich sources include organ meats, beef, lamb, pork, poultry, milk, eggs, cheese, and seafoods such as sardines, salmon, oysters, and tuna. A few plant sources exist, such as tempeh, sea vegetables, brewer’s yeast, spirulina, and mushrooms, but these are less reliable compared to animal sources and may provide a form of the vitamin that is not as useful as animal-derived B₁₂. Some breakfast cereals are fortified with B₁₂.

Recent findings: Studies have continued to support the connection between B₁₂ (and other B vitamins), homocysteine levels in the blood, and heart disease. A recent study, however, found that homocysteine levels may also be a risk factor for chromosomal damage.¹ Researchers have also determined that B₁₂ supplementation is an affordable and nontoxic strategy for preventing irreversible neurological damage among the elderly if started early.² A two-year study found that people with vitiligo, a disorder in which patches of skin lose their color, could induce repigmentation by taking vitamins B₁₂ and folic acid in combination with exposure to the sun.³

Safety: It is nontoxic up to at least 1,000 mcg per day, much beyond the optimal level. Vitamin B₁₂ supplements are not associated with side effects. If a person is deficient in vitamin B₁₂ and takes 1,000 mcg of folic acid per day or more, the folic acid can improve anemia caused by the B₁₂ deficiency, but not affect neurological symptoms of a B₁₂ deficiency. Vitamin B₁₂ deficiencies often occur without anemia (even in people who don’t take folic acid supplements). Some doctors do not know that the absence of anemia does not rule out a B₁₂ deficiency. If this confusion delays diagnosis of a vitamin B₁₂ deficiency, the patient could be permanently injured. This problem is rare, and should not happen with doctors knowledgeable in this area using correct testing procedures. Anyone supplementing with more than 1,000 mcg per day of folic acid should seek evaluation by a nutrition-savvy medical practitioner.

Types of products: As an individual supplement B₁₂ comes in tablets, capsules, liquids, and lozenges; some forms are sublingual. Potency ranges from 100 to 10,000 mcg. Injectable B₁₂ offers no advantages over oral supplements. B₁₂ is sometimes combined with folic acid. It is included in most B complex and multi-nutrient formulas. The most common form in supplements is cyanocobalamin; hydroxycobalamin and methylcobalamin are also found.

References

1. Fenech, M., et al., "Folate, vitamin B12, homocysteine status and DNA damage in young Australian adults," Carcinogenesis (1998), 19(7):1163–71
2. Nilsson-Ehle, H., "Age-related changes in cobalamin (vitamin B12) handling. Implications for therapy," Drugs Aging (1998), 12(4):277–92
3. Juhlin, L., and M.J. Olsson, "Improvement of vitiligo after oral treatment with vitamin B12 and folic acid and the importance of sun exposure," Acta Derm Venereol (1997), 77(6):460–62