Vitamin B12
Overview
All B vitamins are water-soluble,
meaning that the body does not store them. Vitamin B12, also called
cobalamin, is one of 8 B vitamins. It is important to know that all
B vitamins help the body convert food (carbohydrates) into fuel
(glucose), which is used to produce energy. These B vitamins,
commonly referred to as B complex vitamins, also help the body use
fats and protein. B complex vitamins are also used for healthy skin,
hair, eyes, and liver. They help the nervous system function
properly.
Vitamin B12 is an especially important
vitamin for maintaining healthy nerve cells, and it helps in the
production of DNA and RNA, the body's genetic material. Vitamin B12
also works closely with vitamin B9, also called folate or folic acid,
to help make red blood cells and to help iron work better in the
body. Folate and B12 work together to produce S-adenosylmethionine
(SAMe), a compound involved in immune function and mood.
Vitamins B12, B6, and B9 work together
to control blood levels of the amino acid homocysteine. High levels
of homocysteine are associated with heart disease. However,
researchers aren't sure whether homocysteine is a cause of heart
disease or just a marker that indicates someone may have heart
disease.
It' s rare for young people to be
deficient in vitamin B12, but it' s not uncommon for older people to
be mildly deficient. That may be because their diets are not as
healthy or because they have less stomach acid, which the body needs
to absorb B12. Low levels of B12 can cause a range of symptoms
including fatigue, shortness of breath, diarrhea, nervousness,
numbness, or tingling sensation in the fingers and toes. Severe
deficiency of B12 causes nerve damage.
Others at risk for B12 deficiency
include:
1. Vegans, vegetarians who also don't eat dairy or eggs -- vitamin
B12 is found only in animal products
2. People with problems absorbing nutrients, due to conditions such
as Crohn's disease, pancreatic disease, and people who have had
weight loss surgery
3. People who are infected with Helicobacter pylori, an organism in
the intestines that can cause an ulcer. H. pylori damages stomach
cells that make intrinsic factor, a substance the body needs to
absorb B12
4. People with an eating disorder
5. People with HIV
6. The elderly
Folic acid (vitamin B9), especially
when taken in high doses, can mask the symptoms of a vitamin B12
deficiency. The danger is that without symptoms, someone with a
vitamin B12 deficiency may not know it, and could run the risk of
developing nerve damage. Anyone planning to take more than 800 mcg of
folic acid should talk to their doctor first, to make sure they do
not have a B12 deficiency.
Vitamin B12
Vitamin B12 is
bound to protein in food. The activity of hydrochloric acid and
gastric protease in the stomach releases vitamin B12 from its
protein. Once it is released, vitamin B12 begins to work
quickly. It is important for the formation of red blood cells,
neurological function, and DNA synthesis. It also supports the
digestive system in keeping glucose levels stable.
A simple blood test can determine the
level of B12 in the body. Adults who have a value below 170 to 250
pg/ml are considered deficient in the vitamin. An elevated blood
homocysteine level or elevated methylmalconic acid level may also
suggest a B12 deficiency.
Tests
Vitamin B12 and folate are ordered to
detect deficiencies and to help diagnose the cause of certain
anemias. One type of associated anemia is pernicious anemia, an
autoimmune disease that affects the absorption of B12. This
megaloblastic anemia occurs when the body produces antibodies against
the gastric parietal cells or the intrinsic factor, resulting in B12
malabsorption.
Folate, B12, and an assortment of other
tests may be ordered to help evaluate the general health and
nutritional status of a person with signs of significant malnutrition
or dietary malabsorption. This may include people with alcoholism,
other liver diseases, gastric cancer, and those with malabsorption
conditions such as celiac disease, tropical sprue, Crohn’s disease,
inflammatory bowel disease, and cystic fibrosis.
B12 and folate may also be ordered to
aid in diagnosis when an individual presents with an altered mental
state or other behavioral changes, especially in the elderly. B12 may
be ordered with folate, by itself, or with other screening laboratory
tests (antinuclear antibody, CRP, rheumatoid factor, CBC and
chemistry blood tests) to help establish reasons why a person shows
symptoms of neuropathy.
In those treated for known B12 and
folate deficiencies, these tests will be ordered occasionally to
monitor the effectiveness of treatment. This is especially true in
those who cannot properly absorb B12 and/or folate and must have
lifelong treatment.
Recommended Daily Allowance
If you are considering taking a B12
supplement, ask your health care provider to help you determine the
right dose for you.
Daily recommendations for dietary
vitamin B12 are listed below.
Pediatric
Newborns - 6 months: 0.4 mcg
(adequate intake)
Infants 6 months - 1 year: 0.5
mcg (adequate intake)
Children 1 - 3 years: 0.9 mcg
(RDA)
Children 4 - 8 years: 1.2 mcg
(RDA)
Children 9 - 13 years: 1.8 mcg
(RDA)
Teens 14 - 18 years: 2.4 mcg
(RDA)
Adult
19 years and older: 2.4 mcg
(RDA)*
Pregnant women: 2.6 mcg (RDA)
Breastfeeding women: 2.8 mcg
(RDA)
*Because 10 - 30% of older people may
not absorb B12 from food very well, people over 50 should meet their
daily requirement through either foods fortified with vitamin B12 or
a supplement containing B12.
Cautions
If the B12 deficiency is not remedied,
permanent nerve damage can occur. Neuropathy is a common problem for
people with diabetes, who experience pain, tingling, and numbness in
their arms, hands, legs, and feet, resulting in sores.
Vitamin B12 is an especially important
vitamin for maintaining healthy nerve cells, and it helps in the
production of DNA and RNA, the body's genetic material. Vitamin B12
also works closely with vitamin B9, also called folate or folic acid,
to help make red blood cells and to help iron work better in the
body.
Food Sources
Vitamin B12 is found only in animal
foods. Liver, sardines, and salmon rank highest, with liver running
away with it. Kidney, eggs, beef, and pork are also good sources.
There are no vegetarian sources. Supplements include -
Methylcobalamin is probably the best.
Precautions
One large study found that women who
took 1,000 mcg of vitamin B12 along with 2500 mcg of folic acid and
500 mg of vitamin B6 daily reduced their risk of developing AMD, an
eye disease that can cause loss of vision.
Fatigue is one of the symptoms of a
vitamin B12 deficiency. One preliminary study indicated that people
with chronic fatigue syndrome might benefit from B12 injections,
although more research is needed to know for sure.
Although there is no evidence that
vitamin B12 alone reduces the risk of breast cancer, population
studies have shown that women who get more folate in their diet have
lower risk of breast cancer. Vitamin B12 works with folate in the
body, so it may help contribute to a lesser risk. Another preliminary
study suggested that postmenopausal women who had the lowest amounts
of B12 in their diet had an increased risk for breast cancer.
Studies suggest that vitamin B12
supplements may improve sperm counts and sperm mobility. However, the
studies were of poor quality. Better studies are needed to see
whether B12 has any real effect.
Possible Interactions
If you are currently being treated with
any of the following medications, you should not use vitamin B12
supplements without first talking to your health care provider.
Medications that reduce levels of B12
in the body include:
Anti-seizure medications -- including
phenytoin (Dilantin), phenobarbital, primidone (Mysoline)
Chemotherapy medications --
particularly methotrexate
Colchicine -- used to treat gout
Bile acid sequestrants -- used to lower
cholesterol; include colestipol (Colestid), cholestyramine
(Questran), and colsevelam (Welchol)
H2 blockers -- used to reduce stomach
acid; include cimetidine (Tagamet), famotidine (Pepcid AC),
ranitidine (Zantac)
Metformin (Glucophage) -- medication
taken for diabetes
Proton pump inhibitors -- used to
reduce stomach acid; include esomeprazole (Nexium), lansprazole
(Prevacid), omeprazole (Prilosec), and rabeprazole (Aciphex)
Antibiotics, Tetracycline -- Vitamin
B12 should not be taken at the same time as tetracycline because it
interferes with the absorption and effectiveness of this medication.
Vitamin B12 should be taken at different times of the day from
tetracycline. All vitamin B complex supplements act in this way and
should be taken at different times from tetracycline. In addition,
long-term use of antibiotics can lower vitamin B levels in the body,
particularly B2, B9, B12, and vitamin H (biotin), which is considered
part of the B complex vitamins.