Vitamin B12: What does it do?
is is a water-soluble vitamin needed for normal nerve cell activity, DNA
replication, and production of the mood-affecting substance SAMe (S-adenosyl-L-methionine). 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.
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, because the body’s ability to
absorb large amounts is relatively poor.
Where is Vitamin B12 found?
is found in all foods of animal origin, including dairy,
eggs, meat, poultry, and fish. According to one report, small, inconsistent
amounts occur in seaweed (including nori and chlorella) and tempeh.3 Many researchers and healthcare
professionals believe that people cannot rely on
vegetarian sources to provide predictably sufficient quantities of vitamin B12. However,
another study found substantial amounts of vitamin B12 in nori (at least 55 mcg per 100 grams
of dry weight).4
Who is likely to be deficient of Vitamin B12?
Vegans (vegetarians who also avoid dairy and
eggs) frequently become deficient, though the process often takes many years. People with
malabsorption conditions, including those with
tapeworm infestation and those with bacterial overgrowth in the intestines, often suffer from
vitamin B12 deficiency. Malabsorption of vitamin B12 can also result from pancreatic disease,
the effects of gastrointestinal surgery, or various prescription drugs.5
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 incontinence6 and hearing loss7 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.8 Other studies have also suggested a link between
H. pylori infection and vitamin B12 deficiency.9 10 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 that may be
helped by supplementation.11
HIV-infected patients often have low blood
levels of vitamin B12.12
A disproportionate amount of people with psychiatric disorders are deficient in
B12.13 Significant vitamin B12 deficiency is associated with a doubled risk of
severe depression, according to a study of
physically disabled older women.14
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.15
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.16
17
Low blood levels of vitamin B12 are sometimes seen in pregnant women; however, this does not always indicate
a vitamin B12 deficiency.18 The help of a healthcare professional is needed to
determine when a true vitamin B12 deficiency exists in preg
How much Vitamin B12 is usually taken?
Most people do not require vitamin B12 supplements. However, vegans should supplement with at least 2 to 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.20 21
22 23 24
Absorption of vitamin B12 is reduced with increasing age. Some research suggests that
elderly people may benefit from 10 to 25 mcg per day of vitamin B12.25
26 27
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,28 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 with Vitamin B12?
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.29 30 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.
Are there any drug
interactions?
Certain medicines may interact with vitamin B12. Refer to drug interactions for a list of those medicines.
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The information presented in Healthnotes is for informational
purposes only. It is based on scientific studies (human, animal, or in
vitro), clinical experience, or traditional usage as cited in each article.
The results reported may not necessarily occur in all individuals. For many of
the conditions discussed, treatment with prescription or over the counter
medication is also available. Consult your doctor, practitioner, and/or
pharmacist for any health problem and before using any supplements or before
making any changes in prescribed medications.
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