Herbs & Supplements:
Vitamin B12

Supplement Forms / Alternate Names
  • Methylcobalamin, Cyanocobalamin, Hydrocobalamin, Cobalamin
Principal Proposed Uses
  • Correcting Deficiency
Other Proposed Uses
  • Male Infertility, Asthma, HIV Support, Amyotrophic Lateral Sclerosis (Lou Gehrig's Disease), Diabetic Neuropathy, Multiple Sclerosis, Restless Legs Syndrome, Tinnitus, Alzheimers Disease, Vitiligo, Depression, Osteoporosis, Periodontal Disease

Vitamin B₁₂, an essential nutrient, is also known as cobalamin. The "cobal" in the name refers to the metal cobalt contained in B₁₂. Vitamin B₁₂ is required for the normal activity of nerve cells, and works with folate and vitamin B₆ to lower blood levels of homocysteine, a chemical in the blood that is thought to contribute to heart disease. B₁₂ also plays a role in the body's manufacture of S-adenosylmethionine, or SAMe.

Anemia is usually (but not always) the first sign of B₁₂ deficiency. Earlier in this century, doctors coined the name "pernicious anemia" for a stubborn anemia that didn't improve even when the patient was given iron supplements. Today we know that pernicious anemia is usually caused by a condition in which the stomach fails to excrete a special substance called intrinsic factor. The body needs the intrinsic factor for efficient absorption of vitamin B₁₂. In 1948, vitamin B₁₂ was identified as the cure for pernicious anemia. B₁₂ deficiency also causes nerve damage, and this may in some cases occur without anemia first developing.

Even in the absence of deficiency, B₁₂ supplements might improve sperm count and mobility, possibly enhancing fertility. Vitamin B₁₂ has also been proposed as a treatment for numerous other conditions, but as yet there is no definitive evidence that it is effective for any purpose other than correcting deficiency.

Requirements/Sources

Extraordinarily small amounts of vitamin B₁₂ suffice for daily nutritional needs. The official U.S. and Canadian recommendations for daily intake are as follows:

• Infants 0–6 months, 0.4 mcg
  7–12 months, 0.5 mcg
• Children 1–3 years, 0.9 mcg
  4–8 years, 1.2 mcg
  9–13 years, 1.8 mcg
• Males and females 14 years and older, 2.4 mcg
• Pregnant women, 2.6 mcg
• Nursing women, 2.8 mcg

Vitamin B₁₂ deficiency is rare in the young, but it's not unusual in older people: Probably 10 to 20% of the elderly are deficient in B₁₂.^1–4 This may be because older people have lower levels of stomach acid. The vitamin B₁₂ in our food comes attached to proteins, and must be released by acid in the stomach in order to be absorbed. When stomach acid levels are low, we don't absorb as much vitamin B₁₂ from our food. Fortunately, vitamin B₁₂ supplements don't need acid for absorption. For this reason, people who take medications that greatly reduce stomach acid, such as Prilosec (omeprazole) or Zantac (ranitidine), should probably also take B₁₂ supplements.^5–10

Stomach surgery and other conditions affecting the digestive tract can also lead to B₁₂ deficiency. Vitamin B₁₂ absorption or levels in the blood may also be impaired by colchicine (for gout), metformin and phenformin (for diabetes), AZT (for AIDS), and nitrous oxide,^11–14 although one recent study found no effect from nitrous oxide.¹⁵ Interestingly, taking extra calcium may improve B₁₂ absorption in individuals using metformin and possibly also in those using phenformin.¹⁶ Slow-release potassium supplements can impair B₁₂ absorption as well.¹⁷

Vitamin B₁₂ is found in most animal foods. Beef, liver, clams, and lamb provide a whopping 80 to 100 mcg of B₁₂ per 3.5-ounce serving, at least 40 times the dietary requirement. Sardines, chicken liver, beef kidney, and calf liver are also good sources, providing between 25 and 60 mcg per serving. Trout, salmon, tuna, eggs, whey, and many cheeses provide at least the recommended daily intake. Nondairy, or total, vegetarians can eventually become B₁₂-deficient, unless they take B₁₂ supplements or eat B₁₂-enriched yeast.

Vitamin B₁₂ is available in three forms: cyanocobalamin, hydrocobalamin, and methylcobalamin. The first is the most widely available and least expensive, but some experts think that the other two forms are preferable.

Therapeutic Dosages

For correcting absorption problems caused by medications, taking vitamin B₁₂ at the level of dietary requirements should suffice.

For other purposes, enormously higher daily doses—ranging from 100 to 2,000 mcg—are sometimes recommended.

Because the B vitamins tend to work together, many nutritional experts recommend taking B₁₂ with other B vitamins in the form of a B-complex supplement.

Therapeutic Uses

It appears that individuals who take medications that dramatically lower stomach acid would profit by taking B₁₂ supplements.^18–23 Other individuals likely to be deficient in B₁₂, such as the elderly, or those taking the medications listed in Requirements/Sources, might well benefit from a daily B₁₂ supplement to prevent B₁₂ deficiency.

Severe B₁₂ deficiency can cause anemia and, potentially, nerve damage. The latter may become permanent if the deficiency is not corrected in time. Anemia most often develops first, leading to treatment before permanent nerve damage develops. (However, folate supplements can get in the way of this "early warning system." This is why people are cautioned against taking high doses of folate without medical supervision. When taken at a dosage higher than 400 mcg daily, folate can prevent anemia caused by B₁₂ deficiency, thereby allowing permanent nerve damage to develop without any warning. Therefore, you should not take folate at high dosages without first getting a blood test to evaluate your B₁₂ levels.)

Mild B₁₂ deficiency (too slight to cause anemia) may impair brain function.^24,25 A study evaluated 34 individuals over 60 years of age with evidence of marginal B₁₂ status, along with 21 control participants with normal B₁₂ levels. Careful measurement of brain function found evidence of impairment in 38.2% of the B₁₂-deficient participants, but in only 9.5% of those with sufficient B₁₂. In addition, treatment with B₁₂ supplements restored normal brain function.

For pernicious anemia, B₁₂ injections are traditionally used but research has shown that oral B₁₂ works just as well, provided you take enough of it (between 300 and 1,000 mcg daily).^26–29

Preliminary evidence suggests that B₁₂ supplements may improve sperm activity and sperm count and perhaps treat male infertility.^30,31

Vitamin B₁₂ is widely recommended as a treatment for asthma,³² but there is little real evidence that it is effective. On the basis of weak and sometimes contradictory evidence, vitamin B₁₂ has been suggested for HIV,^33–37amyotrophic lateral sclerosis,³⁸ diabetic neuropathy,^39,40multiple sclerosis (MS),^41–45restless legs syndrome,^46,47 and tinnitus.⁴⁸

Although vitamin B₁₂ has been proposed as a treatment for Alzheimer's disease, this recommendation is based solely on the results of one small, poorly designed study.⁴⁹ More recent and better-designed studies found little to no benefit.^50,51

Some evidence suggests that people with vitiligo (splotchy loss of skin pigmentation) might be deficient in vitamin B₁₂ and supplementation along with folate may be helpful.^52,53 However, the evidence is very weak and not all studies agree.⁵⁴ Vitamin B₁₂ is also sometimes recommended for numerous other problems, including depression, osteoporosis, and periodontal disease, but there is little to no evidence as yet that it really works.

A double-blind trial of vitamin B₁₂ for seasonal affective disorder (SAD-- a type of depression related to lack to lack of light during the winter) found no evidence of benefit.⁵⁸

What Is the Scientific Evidence for Vitamin B12?

Male Infertility

Vitamin B₁₂ deficiencies in men can lead to reduced sperm counts and lowered sperm mobility. For this reason, B₁₂ supplements have been tried for improving fertility in men with abnormal sperm production. In one double-blind study of 375 infertile men, supplementation with vitamin B₁₂ produced no benefits on average in the group as a whole.⁵⁵ However, in a particular subgroup of men with sufficiently low sperm count and sperm motility, B₁₂ appeared to be helpful. Such "dredging" of the data is suspect from a scientific point of view, however, and this study cannot be taken as proof of effectiveness.

Safety Issues

Vitamin B₁₂ appears to be extremely safe. However, in some cases very high doses of vitamin B₁₂ can cause or worsen acne symptoms.^56,57

Interactions You Should Know About

If you are taking

• Medications that reduce stomach acid such as H₂ blockers—such as Zantac (ranitidine)—and proton pump inhibitors—such as Prilosec (omeprazole)—colchicine, AZT, or if you are exposed to nitrous oxide anesthesia: You may need extra B₁₂.
• Metformin or phenformin: You may need extra B₁₂. Another option is to take extra calcium, which may in turn improve B₁₂ absorption.
• Potassium:You may need extra B₁₂.

Last reviewed March 2002 by Medical Review Board

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