Also indexed as: Pernicious Anemia
An abnormally low level of vitamin B12 (cobalamin) is
a factor in many disorders.
The absorption of dietary vitamin B12 occurs in the small intestine and requires a
secretion from the stomach known as intrinsic factor. If intrinsic factor is deficient,
absorption of vitamin B12 is severely diminished. Vitamin B12 deficiency impairs the
body’s ability to make blood, accelerates blood cell destruction, and damages the
nervous system. The result is pernicious anemia (PA). In the classical definition, PA refers
only to B12 deficiency anemia caused by a lack of intrinsic factor.
True PA is probably an autoimmune disease. The
immune system destroys cells in the stomach that secrete intrinsic factor. Many people
with PA have both chronic inflammation of the stomach lining, called atrophic gastritis, and
antibodies that fight their intrinsic factor-secreting cells.1
The term pernicious anemia is sometimes used colloquially to refer to any anemia caused by
vitamin B12 deficiency. Vitamin B12 deficiency can be due to malabsorption of dietary B12 despite normal levels of
intrinsic factor. For example, celiac disease and
Crohn’s disease may cause B12 malabsorption, which
can lead to anemia. Less common causes of B12 deficiency include gastrointestinal surgery, pancreatic disease, intestinal parasites, and certain drugs. Pregnancy, hyperthyroidism, and advanced stages of cancer may increase the body’s requirement for B12,
sometimes leading to a deficiency state.
Low stomach acid, known as hypochlorhydria,
interferes with the absorption of B12 from food but not from supplements. Aging is associated
with a decrease in the normal secretion of stomach acid. As a result, some older people with
normal levels of intrinsic factor and with no clear cause for malabsorption will become
vitamin B12-deficient unless they take at least a few micrograms per day of vitamin B12 from supplements.
Caution: PA is a serious medical condition. When fatigue, often the
first symptom of PA, is present, a qualified healthcare practitioner should be consulted.
Symptoms of PA can be caused by other conditions, none of which would respond to vitamin B12 supplementation. Moreover, if true vitamin B12
deficiency exists, the cause—lack of intrinsic factor, general malabsorption conditions, lack of stomach acidity, or dietary deficiency—must
also be properly diagnosed by examination and blood tests before the appropriate treatment can
be determined.
Checklist for Vitamin B12
Deficiency
What are the symptoms of vitamin B12 deficiency?
Symptoms of severe vitamin B12 deficiency (regardless of the cause) may include burning of
the tongue, fatigue, weakness, loss of appetite, intermittent constipation and
diarrhea, abdominal pain, weight loss, menstrual symptoms, psychological symptoms, and
nervous system problems, such as numbness and tingling in the feet and hands. Most symptoms
can occur before the deficiency is severe enough to cause anemia. Healthcare professionals
have a series of laboratory tests that can determine B12 deficiency at earlier stages that are
not accompanied by anemia.
Medical treatments
Over the counter supplementation with vitamin B12 may benefit some individuals with mild
deficiency.
Prescription drug treatment for some individuals includes lifelong intramuscular vitamin
B12 injections. The cortisone-like drugs, such as
prednisone (Deltasone®, Orasone®) may also be recommended for some people.
Dietary changes that may be helpful
Vitamin B12 is found in significant amounts only in
animal protein foods—meat and poultry,
fish, eggs, and dairy products. Even small amounts of these foods
supply sufficient amounts of vitamin B12 to provide enough for healthy people.
Except for vegans (vegetarians who also abstain
from eggs, dairy, and other animal products), virtually no one in North America has a diet
deficient in vitamin B12. Those who avoid animal protein foods can easily take vitamin B12
supplements instead. Strict vegans generally develop a dietary deficiency of vitamin B12, but
it is often many years before a deficiency becomes severe enough to cause symptoms or to be
diagnosed. Doctors recommend that all vegans supplement with vitamin B12.
People who lack intrinsic factor or have a
malabsorption condition need to depend on high amounts of vitamin B12 from supplements and
not the lower amounts found in food. Similarly, older people with a vitamin B12
deficiency due to a lack of stomach acid, but not a lack of intrinsic factor, cannot depend on
food-based vitamin B12.
Tempeh, a fermented soybean product, provides some
vitamin B12. However, the B12 content of tempeh is variable and insufficient to meet dietary
B12 requirements.2 Small but inconsistent amounts of B12 also occur in seaweed and
spirulina.3 4 Because of this
variability, most doctors do not recommend vegetable sources of vitamin B12 to replenish
deficient stores. No other vegetables provide vitamin B12, unless they are contaminated with
fecal matter (e.g., fertilizer).
Lifestyle changes that may be helpful
Alcohol abuse can lead to gastritis and damage to
the lining of the intestines, both of which can interfere with vitamin B12 absorption. If B12
deficiency is due to alcoholism, abstinence may prevent
further impairment of B12 absorption.5
Nutritional supplements that may be helpful
Normally, only 3 to 4 mcg per day of vitamin B12 is
required to prevent dietary deficiency. If gastrointestinal function is normal, even these
small amounts of vitamin B12 from oral supplementation can prevent deficiency in
vegans.6 If a deficiency already exists, most doctors will recommend an initial
vitamin B12 injection, then oral amounts ranging from 500 mcg to 1,000 mcg per day until
symptoms subside; this is followed by a maintenance level of approximately 10 mcg per day to
prevent future deficiencies.
In a person with true PA, initial B12 supplementation should begin with an injection given
by a qualified healthcare professional. After blood abnormalities are reversed, maintenance
supplementation can be successfully accomplished with oral vitamin B12 at 1,000 to 2,000 mcg
(1 to 2 mg) per day and does not require further injections.7 In a person lacking
intrinsic factor, only about 1% of this oral amount (10–20 mcg) will be absorbed, but
that amount is more than sufficient to prevent future vitamin B12 deficiency.8
9 Many physicians are unaware of this well-researched option and thus unnecessarily
recommend lifelong B12 injections.10
People with a vitamin B12 deficiency due to a
malabsorption condition must have an appropriate treatment tailored to their individual
needs by a healthcare professional. In older people who have inadequate absorption of vitamin
B12 from food due to low stomach acid, prevention of deficiency can be achieved with small
amounts of supplemental vitamin B12 found in
B-complex and multivitamins. However, if a
deficiency already exists in such people, a vitamin B12 injection is typically the initial
treatment, followed by varying amounts of oral supplemental vitamin B12 depending on the
extent of the deficiency.
Are there any side effects or interactions?
Refer to the individual supplement for information about any side effects or interactions.
Caution: Individuals with vitamin B12 deficiency must not take large
amounts (greater than 800 mcg per day) of folic acid
without the supervision of a doctor. At high levels, folic acid can mask the signs of vitamin
B12 deficiency, potentially resulting in serious and irreversible nerve damage.
References
1. Beers MH, Berkow R, eds. The Merck Manual, 17th ed.
Whitehouse Station, NJ: Merck and Co., Inc., 1999, 868.
2. Areekul S, Pattanamatum S, Cheeramakara C, et al. The source and
content of vitamin B12 in the tempehs. J Med Assoc Thai 1990;73:152–6.
3. Dagnelie PC, van Staveren WA, van den Berg H. Vitamin B-12 from algae
appears not to be bioavailable. Am J Clin Nutr 1991;53:695–7. Published erratum
appears in Am J Clin Nutr 1991;53:988.
4. Rauma AL, Torronen R, Hanninen O, Mykkanen H. Vitamin B-12 status of
long-term adherents of a strict uncooked vegan diet (“living food diet”) is
compromised. J Nutr 1995;125:2511–5.
5. Gozzard DI. Experiences with dual protein bound aqueous vitamin B12
absorption test in subjects with low serum vitamin B12 concentrations. J Clin Pathol
1987;40:633–7.
6. Little DR. Ambulatory management of common forms of anemia. Am Fam
Physician 1999;59:1598–604.
7. Kuzminski AM, Del Giacco EJ, Allen RH, et al. Effective treatment of
cobalamin deficiency with oral cobalamin. Blood 1998;92:1191–8.
8. Kondo H. Haematological effects of oral cobalamin preparations on
patients with megaloblastic anaemia. Acta Haematol 1998;9:200–5.
9. Berlin R, Berlin H, Brante G, Pilbrant A. Vitamin B12 body stores
during oral and parenteral treatment of pernicious anaemia. Acta Med Scand
1978;204:81–4.
10. Lederle FA. Oral cobalamin for pernicious anemia. Medicine’s
best kept secret? JAMA 1991;265(1):94–5.
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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
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before making any changes in prescribed medications. Information expires March 2005.
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