Vitamin B12

Vitamin B12

Also indexed as: Adenosylcobalamin, Cobalamin, Cyanocobalamin, Hydroxocobalamin, Hydroxycyanocobalamin, Methylcobalamin

* What it does
* Where found
* Helpful for
* Are you deficient?
* Amount to take
* Safety check
* References

What does it do?

Vitamin B12 is needed for normal nerve cell activity, DNA replication, and production of the mood-affecting substance SAMe (S-adenosyl-L-methionine). Vitamin B12 acts with folic acid and vitamin B6 to control homocysteine levels. An excess of homocysteine is associated with an increased risk of heart disease, stroke, and potentially other diseases such as osteoporosis and Alzheimer?s disease.

Vitamin B12 deficiency causes fatigue. Years ago, a small, double-blind trial reported that even some people who are not deficient in this vitamin had increased energy after vitamin B12 injections, compared with the effect of placebo injections.1 In recent years, however, the relationship between B12 injections and the energy level of people who are not vitamin B12-deficient has been rarely studied. In a preliminary trial, 2,500?5,000 mcg of vitamin B12, given by injection every two to three days, led to improvement in 50?80% of a group of people with chronic fatigue syndrome (CFS), with most improvement appearing after several weeks of vitamin B12 shots.2 The ability of vitamin B12 injections to help people with CFS remains unproven, however. People with CFS interested in considering a trial of vitamin B12 injections should consult a doctor. Oral or sublingual (administered under the tongue) B12 supplements are unlikely to obtain the same results as injectable B12, since the body?s ability to absorb large amounts is relatively poor.

Where is it found?

Vitamin B12 is found in all foods of animal origin, including dairy, eggs, meat, poultry, and fish. Small, inconsistent amounts occur in seaweed (including nori and chlorella) and tempeh.3 However, many researchers and healthcare professionals believe that people cannot rely on vegetarian sources to provide predictably sufficient quantities of vitamin B12.

Vitamin B12 has been used in connection with the following conditions (refer to the individual health concern for complete information):
Rating Health Concerns
3 Stars Depression (in people with vitamin B12 deficiency)
High homocysteine (combination with folic acid and vitamin B6)
Pernicious anemia
2 Stars Age-related cognitive decline (in people with vitamin B12 deficiency)
Bell?s palsy
Canker sores (for deficiency only)
Chronic fatigue syndrome
Cystic fibrosis (in people with vitamin B12 deficiency)
Infertility (male)
Low back pain (in combination with vitamin B1 and vitamin B6)
Sickle cell anemia (for sickle cell patients with B12 deficiency)
1Star Alzheimer?s disease
Asthma
Atherosclerosis
Bipolar disorder
Bursitis
Crohn?s disease
Dermatitis herpetiformis (in people with vitamin B12 deficiency)
Diabetes
Heart attack
Hepatitis
HIV support
Hives
Immune function
Insomnia
Lung cancer (reduces risk)
Osteoporosis (to lower homocysteine)
Pain
Phenylketonuria (in people with vitamin B12 deficiency)
Pre- and post-surgery health
Preeclampsia
Retinopathy (associated with childhood diabetes)
Schizophrenia
Seborrheic dermatitis (injection)
Shingles (herpes zoster)/postherpetic neuralgia (injection)
Stroke
Tinnitus (injection)
Vitiligo

Who is likely to be deficient?

Vegans ( vegetarians who also avoid dairy and eggs) frequently become deficient, though the process often takes many years. People with malabsorption conditions often suffer from vitamin B12 deficiency, including those with tapeworm infestation and those with bacterial overgrowth in the intestines. Malabsorption of vitamin B12 can also result from pancreatic disease, the effects of gastrointestinal surgery or various prescription drugs.4

Pernicious anemia is a special form of vitamin B12 malabsorption due to impaired ability of certain cells in the stomach to make intrinsic factor?a substance needed for normal absorption of vitamin B12. By definition, all people with pernicious anemia are vitamin B12-deficient. They require either vitamin B12 injections or oral supplementation with very high levels (1000 mcg per day) of vitamin B12.

Older people with urinary incontinence5 and hearing loss6 have been reported to be at increased risk of B12 deficiency.

Infection with Helicobacter pylori, a common cause of gastritis and ulcers, has been shown to cause or contribute to adult vitamin B12 deficiency. H. pylori has this effect by damaging cells in the stomach that make intrinsic factor?a substance needed for normal absorption of vitamin B12. In one trial, H. pylori was detected in 56% of people with anemia due to vitamin B12 deficiency. Successful eradication of H. pylori led to improved blood levels of B12 in 40% of those infected.7 Other studies have also suggested a link between H. pylori infection and vitamin B12 deficiency.8 9 Elimination of H. pylori infection does not always improve vitamin B12 status. People with H. pylori infections should have vitamin B12 status monitored.

In a preliminary report, 47% of people with tinnitus and related disorders were found to have vitamin B12 deficiencies and may benefit from supplementation.10

HIV-infected patients often have low blood levels of vitamin B12.11

A disproportionate amount of people with psychiatric disorders are deficient in B12.12 Significant vitamin B12 deficiency is associated with a doubled risk of severe depression, according to a study of physically disabled older women.13

A preliminary study found that postmenopausal women who were in the lowest one-fifth of vitamin B12 consumption had an increased risk of developing breast cancer.14

Although blood levels of vitamin B12 may be higher in alcoholics, actual body stores of vitamin B12 in the tissues (e.g., the liver) of alcoholics is frequently deficient.15 16

Low blood levels of vitamin B12 are sometimes seen in pregnant women, however, this does not always indicate a vitamin B12 deficiency.17 The help of a healthcare professional is needed to determine when a true vitamin B12 deficiency exists in pregnant women with low blood levels of the vitamin.

How much is usually taken?

Most people do not require vitamin B12 supplements. However, vegans should supplement with at least 2?3 mcg per day.

People with pernicious anemia are often treated with injections of vitamin B12. However, oral administration of 1,000 mcg per day can be used reliably as an alternative to vitamin B12 injections.18 19 20 21 22

Absorption of vitamin B12 is reduced with increasing age. Some research suggests that elderly people may benefit from 10?25 mcg per day of vitamin B12.23 24 25

When vitamin B12 is used for therapeutic purposes other than correcting a deficiency, injections are usually necessary to achieve results.

Sublingual forms of vitamin B12 are available,26 but there is no proof (nor is there any reason to expect) that they offer any advantage to oral supplements (i.e. a sublingual preparation is eventually swallowed).

Are there any side effects or interactions? Oral vitamin B12 supplements are not generally associated with any side effects.

Although quite rare, serious allergic reactions to injections of vitamin B12 (sometimes even life-threatening) have been reported.27 28 Whether these reactions are to the vitamin itself, or to preservatives or other substances in the injectable vitamin B12 solution, remains somewhat unclear. Most, but not all, injectable vitamin B12 contains preservatives.

If a person is deficient in vitamin B12 and takes 1,000 mcg or more of folic acid per day, the folic acid supplementation can improve the anemia caused by vitamin B12 deficiency. The effect of folic acid on vitamin B12 deficiency-induced anemia is not a folic acid toxicity. Rather, the folic acid supplementation is acting to correct one of the problems caused by B12 deficiency. The other problems caused by a lack of vitamin B12 (mostly neurological) do not improve with folic acid supplements, and can become irreversible if vitamin B12 is not provided to someone who is vitamin B12 deficient.

Some doctors are unaware that vitamin B12 deficiencies often occur without anemia?even in people who do not take folic acid supplements. This lack of knowledge can delay diagnosis and treatment of people with vitamin B12 deficiencies. This can lead to permanent injury. When such a delayed diagnosis occurs in someone who inadvertently erased the anemia of vitamin B12 deficiency by taking folic acid supplements, the folic acid supplementation is often blamed for the missed diagnosis. This problem is rare and should not occur in people whose doctors understand that a lack of anemia does not rule out a vitamin B12 deficiency. Anyone supplementing 1,000 mcg or more per day of folic acid should be initially evaluated by a doctor before the folic acid can obscure a proper diagnosis of a possible B12 deficiency.

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