Vitamin B 12 , an essential nutrient, is also known as cobalamin. The cobal in the name refers to the metal cobalt contained in B 12 . Vitamin B 12 is required for the normal activity of nerve cells and works with folate and vitamin B 6 to lower blood levels of ]]>homocysteine]]> , a chemical in the blood that might contribute to heart disease. B 12 also plays a role in the body's manufacture of ]]>S-adenosylmethionine (SAMe)]]> .

Anemia is usually (but not always) the first sign of B 12 deficiency. Earlier in this century, doctors coined the name "pernicious anemia" for a stubborn form of anemia that didn't improve even when the patient was given iron supplements. Today we know that pernicious anemia comes about when the stomach fails to excrete a special substance called intrinsic factor. The body needs the intrinsic factor for efficient absorption of vitamin B 12 . In 1948, vitamin B 12 was identified as the cure for pernicious anemia. B 12 deficiency also causes nerve damage, and this may, in some cases, occur without anemia first developing.

Vitamin B 12 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.



Extraordinarily small amounts of vitamin B 12 suffice for daily nutritional needs. The official US 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 B 12 deficiency is rare in the young, but it's not unusual in older people: Probably 10% to 20% of the elderly are deficient in B 12 . 1-4]]> This may be because older people have lower levels of stomach acid. The vitamin B 12 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 B 12 from our food. Fortunately, vitamin B 12 supplements don't need acid for absorption and should, therefore, get around this problem. However, for reasons that are unclear, one study found that B 12 -deficient seniors need very high dosages of the supplements to normalize their levels, as high as 600 to 1,000 mcg daily. ]]>65]]>

Similarly, people who take medications that greatly reduce stomach acid, such as ]]>omeprazole]]> (Prilosec) or ]]>ranitidine]]> (Zantac) also may have trouble absorbing B 12 from food and could benefit from supplementation. ]]>5-10]]>

Stomach surgery and other conditions affecting the digestive tract can also lead to B 12 deficiency. Vitamin B 12 absorption or levels in the blood may also be impaired by ]]>colchicine]]> (for gout), ]]>metformin and phenformin]]> (for diabetes), and ]]>AZT]]> (for AIDS). ]]>11,12,69]]> Exposure to nitrous oxide (such as may be experienced by dentists and dental hygienists) might cause B 12 deficiency, but studies disagree. ]]>14,15]]> Slow-release potassium supplements might impair B 12 absorption as well. ]]>17]]>

Vitamin B 12 is found in most animal foods; it is also found only in animal food. Beef, liver, clams, and lamb provide a whopping 80 to 100 mcg of B 12 per 3.5-oz 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.

Note : Total vegetarians (vegans) must take vitamin B 12 supplements or consume B 12 -fortified foods, or they will eventually become deficient. ]]>59,60]]> Contrary to some reports, seaweed and tempeh do not provide B 12 . (Some forms of blue-green algae, such as ]]>spirulina]]> , contain B 12 , but it is not in an absorbable state. ]]>61]]> )

Vitamin B 12 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.

Severe B 12 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 B 12 deficiency, thereby allowing permanent nerve damage to develop without any warning. More mild deficiencies of vitamin B 12 may cause elevated levels of homocysteine in the blood, potentially increasing risk of heart disease. (See the ]]>Homocysteine]]> article for more information.) Mild B 12 deficiency (too slight to cause anemia) may also impair brain function. ]]>24,25]]>


Therapeutic Dosages

For correcting absorption problems caused by medications, taking vitamin B 12 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.

Therapeutic Uses

It appears that individuals who take medications that dramatically lower stomach acid, such as H2 blockers]]> or ]]>proton pump inhibitors]]> , would benefit by taking B 12 supplements. ]]>18-23]]> Other individuals likely to be deficient in B 12 , such as the elderly, or those taking the medications listed in Requirements/Sources, might well benefit from a daily B 12 supplement to prevent B 12 deficiency.

For pernicious anemia, B 12 injections are traditionally used but research has shown that oral B 12 works just as well, provided you take enough of it (between 300 and 1,000 mcg daily). ]]>26-29]]>

Weak evidence suggests that B 12 supplements may improve sperm activity and sperm count; on this basis, they could be useful for ]]>male infertility]]> . ]]>30,31]]> Some cases of ]]>recurrent miscarriage]]> might be due to vitamin B 12 deficiency. ]]>62]]>

One placebo-controlled, double-blind study, enrolling 49 people with eczema, found benefit with a cream containing vitamin B 12 at a concentration of 0.07%. ]]>66]]> Topical B 12 is hypothesized to work for eczema by reducing local levels of the substance nitric oxide (not related to nitrous oxide).

On the basis of weak and sometimes contradictory evidence, vitamin B 12 has been suggested for ]]>HIV]]> , ]]>33-37]]>]]>amyotrophic lateral sclerosis]]> , ]]>38]]>]]>carpal tunnel syndrome]]> , ]]>67]]>]]>diabetic neuropathy]]> , ]]>39,40]]>]]>multiple sclerosis (MS)]]> , ]]>41-45]]>]]>restless legs syndrome]]> , ]]>46,47]]> and ]]>tinnitus]]> . ]]>48]]>

Some evidence suggests that people with ]]>vitiligo]]> (splotchy loss of skin pigmentation) might be deficient in vitamin B 12 , and supplementation along with folate may be helpful. ]]>52,53]]> However, the evidence is very weak and not all studies agree. ]]>54]]>

Some alternative practitioners recommend the use of injected vitamin B 12 for ]]>Bell’s palsy]]> . However, the only scientific support for this approach comes from one study that was not double-blind. ]]>63]]> (For information on the importance of a double-blind design, see ]]>Why Does This Database Rely on Double-blind Studies?]]> )

Vitamin B 12 is also sometimes recommended for numerous other problems, including ]]>asthma]]> , ]]>depression]]> , ]]>osteoporosis]]> , and ]]>periodontal disease]]> , but there is essentially no evidence as yet that it really works.

A double-blind trial of vitamin B 12 for seasonal affective disorder (SAD—a type of ]]>depression]]> related to lack to lack of light during the winter) failed to find evidence of benefit. ]]>58]]>

One double-blind, placebo-controlled study of 140 people with mildly low B 12 levels failed to find the supplement helpful for improving mental function and mood. ]]>68]]>

Another study failed to find evidence that vitamin B 12 improved general sense of ]]>wellbeing]]> among seniors with signs of mild B 12 deficiency. ]]>64]]>

Although vitamin B 12 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. ]]>50,51,70]]>


What Is the Scientific Evidence for Vitamin B 12 ?

Vitamin B 12 deficiencies in men can lead to reduced sperm counts and lowered sperm mobility. For this reason, B 12 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 B 12 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, B 12 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 B 12 appears to be extremely safe. However, in some cases very high doses of the vitamin can cause or worsen acne symptoms. 56,57]]>


Interactions You Should Know About

If you are taking:

Colchicine]]> , ]]>AZT]]> , medications that reduce stomach acid (such as the ]]>H2 blocker]]> ranitidine [Zantac] or the ]]>proton pump inhibitor omeprazole]]> [Prilosec], ]]>oral hypoglycemics]]> (such as metformin or phenformin), slow-release potassium supplements, or if you are exposed to nitrous oxide anesthesia: You may need extra B 12 . Another option is to take extra ]]>calcium]]> , which may, in turn, improve B 12 absorption.