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Vitamin B12

Vitamin B12

Description

Cobalamin, also known as B12, is a member of the water-soluble family of B vitamins. It is a key factor in the body's proper use of iron and formation of red blood cells. The nervous system also relies on an adequate supply of cobalamin to function appropriately, as it is an essential component in the creation and maintenance of the myelin sheath that lines nerve cells. Other roles of cobalamin include working with pyridoxine (vitamin B6 and folic acid to reduce harmful homocysteine levels, participating in the metabolization of food, and keeping the immune system operating smoothly.

General use

Very small amounts of cobalamin are needed to maintain good health. The RDA value is 0.3 micrograms (mcg) for infants under 6 months, 0.5 mcg for those 6 months to 1 year old, 0.7 mcg for children 1-3 years old, 1.0 mcg for children 4-6 years old, 1.4 mcg for children 7-10 years old, and 2 mcg for those 11 years of age and older. Requirements are slightly higher for pregnant (2.2 mcg) and lactating (2.6 mcg) women.

The primary conditions that benefit from supplementation with cobalamin are megaloblastic and pernicious anemia . Megaloblastic anemia is a state resulting from an inadequate intake of cobalamin, to which vegans are particularly susceptible because of the lack of animal food sources. Vegans, who do not consume any animal products including meat, dairy, or eggs, should take at least 2 mcg of cobalamin per day in order to prevent this condition. In the case of pernicious anemia, intake may be appropriate but absorption is poor due to a lack of normal stomach substance, called intrinsic factor, that facilitates absorption of vitamin B12. Large doses are required to treat pernicious anemia, which occurs most commonly in the elderly population as a result of decreased production of intrinsic factor by the stomach. Supplements are generally effective when taken orally in very large amounts (300-1000 mcg/day) even if no intrinsic factor is produced. These supplements require a prescription, and should be administered with the guidance of a health care provider. Injections, instead of the supplements, are often used.

Those who have infections, burns , some types of cancer , recent surgery, illnesses that cause decay or loss of strength, or high amounts of stress may need more than the RDA amount of B12 and other B vitamins. A balanced supplement is the best approach.

Male infertility can sometimes be resolved through use of cobalamin supplements. Other conditions that may be improved by cobalamin supplementation include: asthma, atherosclerosis (hardening of the arteries caused by plaque formation in the arteries), bursitis (inflammation of a bodily pouch, especially the shoulder or elbow), Crohn's disease (chronic recurrent inflammation of the intestines), depression , diabetes, high cholesterol, osteoporosis , and vitiligo (milky-white patches on the skin). There is not enough evidence to judge whether supplementation for these diseases is effective.

Preparations

Natural sources

Usable cobalamin is only found naturally in animal source foods. Fresh food is best, as freezing and exposure to light may destroy some of the vitamin content. Clams and beef liver have very high cobalamin levels. Other good sources include chicken liver, beef, lamb, tuna, flounder, liverwurst, eggs, and dairy products. Some plant foods may contain cobalamin, but it is not in a form that is usable by the body.

Supplemental sources

Cobalamin supplements are available in both oral and injectable formulations. A nasal gel is also made. Generally a balanced B-complex vitamin is preferable to taking high doses of cobalamin unless there is a specific indication for it, such as megaloblastic anemia. Strict vegetarians will need to incorporate a supplemental source of B12 in the diet. Cyanocobalamin is the form most commonly available in supplements. Two other, possibly more effective, types are hydrocobalamin and methyl-cobalamin. As with all supplements, cobalamin should be stored in a cool, dry, dark place and out of the reach of children.

Deficiency

Cobalamin deficiency may be manifested as a variety of symptoms since cobalamin is so widely used in the body. Severe fatigue may occur initially. Effects on the nervous system can be wide-ranging, and include weakness, numbness and tingling of the limbs, memory loss , confusion, delusion, poor balance and reflexes, hearing difficulties, and even dementia . Severe deficiency may appear similar to multiple sclerosis . Nausea and diarrhea are possible gastrointestinal signs. The anemia that results from prolonged deficiency may also be seen as a pallor, especially in mucous membranes such as the gums and the lining of the inner surface of the eye.

Megaloblastic anemia is a common result of inadequate cobalamin. This condition can also result if a person stops secreting enough intrinsic factor in the stomach, a substance essential for the absorption of cobalamin. Inadequate intrinsic factor leads to pernicious anemia, so called because it persists despite iron supplementation. Long-term deficiencies of cobalamin also allow homocysteine levels to build up. Negative effects of large amounts of circulating homocysteine include heart disease , and possibly brain toxicity. Taking high levels of folic acid supplements can mask cobalamin deficiency and prevent the development of megaloblastic anemia, but neurological damage can still occur. This damage may become permanent if the cobalamin deficiency persists for a long period of time.

Risk factors for deficiency

The primary groups at risk for cobalamin deficiency are vegans who are not taking supplements, and the elderly. Older adults are more likely to have both insufficient intrinsic factor secreted by the stomach and low levels of stomach acid, causing cobalamin to be poorly absorbed. Malabsorptive diseases and stomach surgery can also predispose to a deficiency.

Precautions

People who are sensitive to cobalamin or cobalt should not take cobalamin supplements. Symptoms of hypersensitivity may include swelling, itching , and shock. Adverse effects resulting from B12 supplementation are rare. Cobalamin should also be avoided by those who have a type of hereditary optic nerve atrophy known as Leber's disease.

Side effects

Very high doses of cobalamin may sometimes cause acne .

Interactions

Large amounts of vitamin C taken within an hour of vitamin B supplements will destroy the cobalamin component. Absorption of cobalamin is also impaired by deficiencies of folic acid, iron, or vitamin E . Improved absorption occurs when it is taken with other B vitamins or calcium . Some medications may also cause an increased use or decreased absorption of this vitamin. Those on colchicine, corticosteroids, methotrexate, metformin, phenformin, oral contraceptives, cholestyramine, colestipol, clofibrate, epoetin, neomycin, or supplemental potassium may need extra cobalamin. Use of nicotine products or excessive alcohol can deplete B12.

Resources

BOOKS

Bratman, Steven, and David Kroll. Natural Health Bible. CA Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. PA: Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: The Complete Guide. AZ: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database. CA: Therapeutic Research Faculty, 1999.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: Alpha Books, 1997.

Judith Turner

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Vitamin B12

Vitamin B12

Vitamin B12 was discovered simultaneously by two research teams, one in the United States and one in England. It was the culmination of an intensive worldwide search for a compound that could effectively treat pernicious anemia.

B12 and Liver

During the 1930s, researchers around the world began trying to isolate the active ingredient in liver that contained its curative properties. The "antipernicious anemia factor" was believed to be a B vitamin. It was even given the name B12 long before it was isolated.

Testing was surprisingly slow. Patients were fed extracts of liver rather than the liver itself, but for some reason researchers could not measure the amount of vitamin B12 these liver extracts contained. They could only guess at the extracts' potency by measuring red blood cell growth in each patient's blood.

For years, Karl Folkers, an American chemist at a prominent pharmaceutical company, had been directing a research team that was working on the problem. In 1948, the group finally came up with a solution. They found they could measure the vitamin indirectly by measuring the growth rate of certain bacteria that needed vitamin B12 to grow. This system speeded the purification process of the vitamin enormously.

The New Vitamin

The new vitamin was a large and complicated molecule roughly four times the size of a penicillin molecule. The molecule was so complex that its structure could only be worked out through the aid of advanced technology. In 1956 English physicist Dorothy Hodgkin (1910-) completed the mapping of B12s chemical structure by using x-ray crystallography. She received the 1964 Nobel Prize in chemistry for her work. Vitamin B12 was finally synthesized by Robert Burns Woodward (1917-1979) in 1971, after a ten-year effort.

Pernicious Anemia

Pernicious anemia is a blood disorder in which red blood cells fail to develop normally. The steady decline of red blood corpuscles eventually leads to death. The disease was first described completely in 1849 by English physician Thomas Addison (1793-1860). Addison noted the typical symptoms included increasing weakness and pallor of the patient. This was accompanied by obesity (weight gain) rather than weight loss.

Until the 1920s, this pernicious anemia was always fatal. Then two physicians named George Richards Minot (1885-1950) and William Perry Murphy became inspired by George Whipple's (1878-1976) studies. The Whipple studies showed that beef liver could improve the formation of red corpuscles in anemic dogs. To test Whipple's findings, Minot and Perry began feeding their patients large amounts of beef liver. In 1926, the researchers were able to announce that a daily diet of about a half a pound of liver could control the disease. For their work, Minot, Murphy, and Whipple shared the 1934 Nobel Prize in medicine.

The isolation and synthesis of B12 removed pernicious anemia from the list of deadly medical problems. B12 was the last vitamin to be discovered. Work on the vitamin served to round out the remarkable half-century of vitamin research that began in the 1890s with Dutch physician Christiaan Eijkman (1858-1930).

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vitamin B12

vitamin B12 A cobalt‐containing compound, cobalamin, essential for normal metabolism of folic acid, and hence for cell division. Deficiency leads to pernicious anaemia when immature red blood cell precursors are released into the bloodstream, and there is degeneration of the spinal cord. The absorption of vitamin B12 requires a specific protein (intrinsic factor) which is secreted in the gastric juice and it is failure of absorption, rather than dietary deficiency, that is the more usual cause of the problem. However, B12 is found only in animal foods so vegans have to rely on bacterial preparations.

Meat, eggs, and dairy produce are rich sources and dietary deficiency is unlikely except among vegans.

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vitamin B12

vitamin B12 See COBALAMINE.

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Vitamin B12

Vitamin B12

Description

Cobalamin, also known as B12, is a member of the water-soluble family of B vitamins. It is a key factor in the body's proper use of iron and formation of red blood cells. The nervous system also relies on an adequate supply of cobalamin to function appropriately, as it is an essential component in the creation and maintenance of the myelin sheath that lines nerve cells. Other roles of cobalamin include working with pyridoxine (vitamin B6) and folic acid to reduce harmful homocysteine levels, participating in the metabolization of food, and keeping the immune system operating smoothly.

General use

Very small amounts of cobalamin are needed to maintain good health. The RDA value is 0.3 micrograms (mcg) for infants under six months, 0.5 mcg for those six months to one year old, 0.7 mcg for children one to three years old, 1.0 mcg for children four to six years old, 1.4 mcg for children seven to 10 years old, and 2 mcg for those 11 years of age and older. Requirements are slightly higher for pregnant (2.2 mcg) and lactating (2.6 mcg) women.

The primary conditions that benefit from supplementation with cobalamin are megaloblastic and pernicious anemia. Megaloblastic anemia is a state resulting from an inadequate intake of cobalamin, to which vegans are particularly susceptible because of the lack of animal food sources. Vegans, who do not consume any animal products including meat, dairy, or eggs, should take at least 2 mcg of cobalamin per day in order to prevent this condition. In the case of pernicious anemia, intake may be appropriate but absorption is poor due to a lack of normal stomach substance, called intrinsic factor, that facilitates absorption of vitamin B12. Large doses are required to treat pernicious anemia, which occurs most commonly in the elderly population as a result of decreased production of intrinsic factor by the stomach. Supplements are generally effective when taken orally in very large amounts (300-1000 mcg/day) even if no intrinsic factor is produced. These supplements require a prescription, and should be administered with the guidance of a health care provider. Injections, instead of the supplements, are often used.

Those who have infections, burns, some types of cancer, recent surgery, illnesses that cause decay or loss of strength, or high amounts of stress may need more than the RDA amount of B12 and other B vitamins. A balanced supplement is the best approach.

Male infertility can sometimes be resolved through use of cobalamin supplements. Other conditions that may be improved by cobalamin supplementation include: asthma, atherosclerosis (hardening of the arteries caused by plaque formation in the arteries), bursitis (inflammation of a bodily pouch, especially the shoulder or elbow), Crohn's disease (chronic recurrent inflammation of the intestines), depression, diabetes, high cholesterol, osteoporosis, and vitiligo (milky-white patches on the skin). There is not enough evidence to judge whether supplementation for these diseases is effective.

Preparations

Natural sources

Usable cobalamin is only found naturally in animal source foods. Fresh food is best, as freezing and exposure to light may destroy some of the vitamin content. Clams and beef liver have very high cobalamin levels. Other good sources include chicken liver, beef, lamb, tuna, flounder, liverwurst, eggs, and dairy products. Some plant foods may contain cobalamin, but it is not in a form that is usable by the body.

Supplemental sources

Cobalamin supplements are available in both oral and injectable formulations. A nasal gel is also made. Generally a balanced B-complex vitamin is preferable to taking high doses of cobalamin unless there is a specific indication for it, such as megaloblastic anemia. Strict vegetarians will need to incorporate a supplemental source of B12 in the diet. Cyanocobalamin is the form most commonly available in supplements. Two other, possibly more effective, types are hydro-cobalamin and methyl-cobalamin. As with all supplements, cobalamin should be stored in a cool, dry, dark place and out of the reach of children.

Deficiency

Cobalamin deficiency may be manifested as a variety of symptoms since cobalamin is so widely used in the body. Severe fatigue may occur initially. Effects on the nervous system can be wide-ranging, and include weakness, numbness and tingling of the limbs, memory loss, confusion, delusion, poor balance and reflexes, hearing difficulties, and even dementia. Severe deficiency may appear similar to multiple sclerosis. Nausea and diarrhea are possible gastrointestinal signs. The anemia that results from prolonged deficiency may also be seen as a pallor, especially in mucous membranes such as the gums and the lining of the inner surface of the eye.

Megaloblastic anemia is a common result of inadequate cobalamin. his condition can also result if a person stops secreting enough intrinsic factor in the stomach, a substance essential for the absorption of cobalamin. Inadequate intrinsic factor leads to pernicious anemia, so called because it persists despite iron supplementation. Long-term deficiencies of cobalamin also allow homocysteine levels to build up. Negative effects of large amounts of circulating homocysteine include heart disease and possibly brain toxicity. Taking high levels of folic acid supplements can mask cobalamin deficiency and prevent the development of megaloblastic anemia, but neurological damage can still occur. This damage may become permanent if the cobalamin deficiency persists for a long period of time.

Risk factors for deficiency

The primary groups at risk for cobalamin deficiency are vegans who are not taking supplements, and the elderly. Older adults are more likely to have both insufficient intrinsic factor secreted by the stomach and low levels of stomach acid, causing cobalamin to be poorly absorbed. Malabsorptive diseases and stomach surgery can also predispose to a deficiency.

Precautions

People who are sensitive to cobalamin or cobalt should not take cobalamin supplements. Symptoms of hypersensitivity may include swelling, itching, and shock. Adverse effects resulting from B12 supplementation are rare. Cobalamin should also be avoided by those who have a type of hereditary optic nerve atrophy known as Leber's disease.

Side effects

Very high doses of cobalamin may sometimes cause acne.

Interactions

Large amounts of vitamin C taken within an hour of vitamin B supplements will destroy the cobalamin component. Absorption of cobalamin is also impaired by deficiencies of folic acid, iron, or vitamin E. Improved absorption occurs when it is taken with other B vitamins or calcium. Some medications may also cause an increased use or decreased absorption of this vitamin. Those on colchicine, corticosteroids, methotrexate, metformin, phenformin, oral contraceptives, cholestyramine, colestipol, clofibrate, epoetin, neomycin, or supplemental potassium may need extra cobalamin. Use of nicotine products or excessive alcohol can deplete B12.

KEY TERMS

Homocysteine— An amino acid produced from the metabolization of other amino acids. High levels are an independent risk factor for heart disease.

Megaloblastic anemia— A condition caused by cobalamin deficiency, which is characterized by red blood cells which are too few, too fragile, and abnormally large. Also known as macrocytic anemia.

Pernicious anemia— Megaloblastic anemia resulting from a cobalamin deficiency that is the result of poor absorption due to inadequate production of intrinsic factor in the stomach.

Vegan— A person who doesn't eat any animal products, including dairy and eggs.

Resources

BOOKS

Bratman, Steven, and David Kroll. Natural Health Bible. Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: The Complete Guide. Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database. Therapeutic Research Faculty, 1999.

Pressman, Alan H., and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. Alpha Books, 1997.

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Vitamin B12

Vitamin B12

Definition

Purpose

Description

Precautions

Interactions

Complications

Parental concerns

Resources

Definition

Vitamin B12 is a water-soluble organic compound that the body needs to remain healthy. The only organisms that can make vitamin B12 are bacteria, fungi, yeast, molds, and algae. Humans must get it from foods in their diet. Vitamin B12 is sometimes called cobalamin.

Purpose

Vitamin B12 plays major roles in developing healthy red blood cells, creating new deoxyribose nucleic acid (DNA, genetic material), and in maintaining the health of nerve cells. It is also involved in making certain nutrients available to the body.

Description

Vitamin B12 is one of the least understood vitamins. Although some of its effects were experimentally discovered in the 1930s, Vitamin B12's structure was not determined until the 1960s. Questions still remain about some of its functions. Vitamin B12 is different from other vitamins in several ways. It is the only vitamin not made by any plant or animal, but only by microorganisms. It is the only vitamin to contain the metal cobalt (thus the name cobalamin), and it is the only vitamin that must combine with another substance, called the intrinsic factor (IF), before it can be absorbed by the body.

Although vitamin B12 is made only by microorganisms, it is found in association with animal protein. In nature, it comes in a variety of chemical forms that the body converts into two active forms of B12. Most B12dietary supplements contain the form called cya-nocobalamin. B12 is included in over-the-counter mul-tivitamins and in vitamin-B-complex supplements. It is also sold as a stand-alone dietary supplement and in an injectable form available only by prescription.

When people eat animal protein-beef, fish, pork, chicken, eggs, milk, cheese-the stomach is stimulated to secrete hydrochloric acid and enzymes that break down the protein and release vitamin B12. B12 then binds with IF, which is made in the stomach. Vitamin B12 cannot be absorbed into the body unless it is combined with IF. Therefore, either an absence of B12 in diet or inability of the stomach to make IF can result in B12 deficiency.

Some fermented bean products such as tofu, tem-peh, natto, tamari, and miso may or may not contain

Vitamin B12

Age Recommended Dietary Allowance
Children 0–6 mos.400 ng (AI)
Children 7–12 mos.500 ng (AI)
Children 1–3 yrs.900 ng
Children 4–8 yrs.1.2 mcg
Children 9–13 yrs.1.8 mcg
Children 14–18 yrs.2.4 mcg
Adults 19> yrs.2.4 mcg
Pregnant women2.6 mcg
Breastfeeding women2.8 mcg
Food Vitamin B12 (mcg)
Mollusks or clams, cooked, 3 oz.84
Calf's liver, cooked, 4 oz.41
Cereal, 100% fortified, 3/4 cup6.0
Salmon, baked or broiled, 4 oz.3.3
Beef, top sirloin, broiled, 3 oz.2.4
Cheeseburger, fast food, double patty1.9
Shrimp, steamed or broiled, 4 oz.1.7
Taco, fast food, 1 large1.6
Cereal, 25% fortified1.5
Tuna, white, canned in water, 3 oz.1.0
Milk, 1 cup0.9
Ham, canned or roasted, 3 oz.0.6
Chicken breast, roasted, ½ breast0.3
Egg, 1 whole, cooked0.3
AI = Adequate intake 
mcg = microgram 
ng = nanogram 

(Illustration by GGS Information Services/Thomson Gale.)

vitamin B12 depending on which bacteria were used to ferment these products. Nutritional yeast also may or may not contain vitamin B12 depending on the type of yeast used. Consumers should read labels of these products carefully. The best source of vitamin B12 for people who do not eat meat or animal products is fortified breakfast cereal. Cereals can be fortified at various strengths, ranging from in amounts ranging from 100% of the daily requirement to 25% of the daily requirement. The label must contain information about vitamin fortification.

Vitamin B12's role in health

Vitamin B12 is crucial to the development of healthy red blood cells. As red blood cells mature, they need new DNA. In the absence of adequate vitamin B12, the new DNA is defective. This results in red blood cells that are too large and poorly shaped. These malformed cells have a reduced ability to carry oxygen and result in pernicious anemia or megaloblastic anemia.

Vitamin B12 also is necessary to maintain healthy nerves. Nerves are covered with a fatty sheath called myelin. The myelin covering is necessary for effective transmission of nerve impulses. When vitamin B12 is absent, the myelin sheath does not form correctly.

Proteins in the diet are broken down into small molecules called amino acids that are then used by the body to build new proteins. Vitamin B12 helps make amino acid available to the body. High levels of one particular amino acid, homocysteine, are associated with increased risk of heart disease. Vitamin B12, along with vitamin B6 and folic acid help reduce the level of homocysteine in the blood. Vitamin B12 is also thought to play a role in making carbohydrates and fats available to the body. Clinical trials are underway to determine safety and effectiveness of vitamin B12 in a variety of situations. Individuals interested in participating in a clinical trial at no charge can find a list of open trials at <http://www.clinicaltrials.gov>.

Normal vitamin B12 requirements

The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97–98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

The IOM has not set RDAs for vitamin B12 in children under one year old because of incomplete scientific information. Instead, it has set AI levels for this age group. No UL levels have been set for any age group because no negative (toxic) side effects have been found with B12, even when people have taken many hundreds of times the RDA for years. RDAs for vitamin B12 for people three years and older are measured in micrograms (mcg).

The following are the RDAs and IAs for vitamin B12 for healthy individuals:

  • children birth–6 months: AI 400 nanograms
  • children 7–12 months: AI 500 nanograms
  • children 1–3 years: RDA 900 nanograms
  • children 4–8 years: RDA 1.2 mcg
  • children 9–13 years: RDA 1.8 mcg
  • people 14 years and older: RDA 2.4 mcg

KEY TERMS

Amino acid —Molecules that are the basic building blocks of proteins.

Dietary supplement —A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual's diet with the expectation that it will improve health.

Enzyme —A protein that change the rate of a chemical reaction within the body without themselves being used up in the reaction.

Vitamin —A nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet.

Water-soluble vitamin —A vitamin that dissolves in water and can be removed from the body in urine.

  • pregnant women: RDA 2.6 mcg;
  • breastfeeding women: RDA 2.8 mcg

Sources of vitamin B12

Vitamin B12 is found in food that comes from animals, including meat, fish, poultry, eggs, milk, and cheese. It is also added to fortified breakfast cereals and is found in some fermented bean products. Heating or cooking foods does not reduce their vitamin B12 content very much.

The following list gives the approximate vitamin B12 content for some common foods:

  • calf s liver, cooked, 4 ounces: 41 mcg
  • salmon, baked or broiled, 4 ounces: 3.3 mcg
  • shrimp, steamed or boiled, 4 ounces: 1.7 mcg
  • mollusks or clams, cooked, 3 ounces: 84 mcg
  • tuna, white, canned in water, 3 ounces: 1.0 mcg
  • beef, top sirloin, broiled, 3 ounces: 2.4 mcg
  • cheeseburger, fast food, double patty: 1.9 mcg
  • taco, fast food, 1 large: 1.6 mcg
  • ham, canned or roasted, 3 ounces: 0.6 mcg
  • chicken breast, roasted, 1/2 breast: 0.3mcg
  • milk, 1 cup: 0.9 mcg
  • egg, 1 whole, cooked: 0.3 mcg
  • breakfast cereal, fortified 100%, 3/4 cup: 6.0 mcg
  • breakfast cereal, fortified 25%, 3/4 cup: 1.5 mcg

Vitamin B12 deficiency

Vitamin B12 deficiency is hard to determine, and there is little agreement on how many people are vitamin B12 deficient. This is partly because the body can store 5–10 year's worth of vitamin B12, so symptoms of deficiency are slow to show up, especially in adults. Researchers estimate that anywhere from 300,000–3 million Americans are vitamin B12 deficient.

Most meat-eating Americans get enough vitamin B12 from diet alone. However, the elderly are at higher risk than younger people of developing mild vitamin B12 deficiency. Other people at greater risk of vitamin B12 deficiency include:

  • vegans who eat no animal products
  • breastfed babies of vegan mothers
  • people who have had part of their stomach or intestine removed
  • people with diseases that interfere with the absorption of nutrients such as Crohn's disease, celiac disease, or ulcerative colitis.
  • people with alcoholism
  • people with liver or kidney damage
  • people with HIV/AIDS

Symptoms of vitamin B12 deficiency include shaky movements, loss of balance, muscle weakness and spasms, vision problems, reduced mental functioning, and changes in mood and mental state. These symptoms are quite general and have many other causes besides vitamin B12 deficiency.

Precautions

Breast-fed infants of strict vegan mothers are particularly likely to develop vitamin B12 deficiency, as they have little or no B12 stored in their bodies at birth. Failure to get enough B12 during the infancy and childhood can result in permanent damage to the nervous system. Vegan mothers should consult a pediatrician about appropriate Vitamin B12 supplementation.

Individuals with the eye disorder Leber's optic atrophy should not use vitamin B12 supplements. High levels of B12 will accelerate degeneration of the optic nerve, leading to blindness.

Folic acid may mask vitamin B12 deficiency. Folic acid supplements will reverse anemia symptoms, but they do not stop nerve damage caused by B12 deficiency. Permanent nerve damage may result. People with suspected folic acid deficiency who begin taking folic acid supplements should also be evaluated for vitamin B12 deficiency.

Interactions

Many drugs used to treat gastroesophageal reflux disease (GERD) such as omeprazole (Prilosec), lanso-prazole (Prevacid), cimetidine (Tagamet), famotidine (Pepsid), nizatidine (Axid), or ranitidine (Zantac) decrease the amount of hydrochloric acid secreted by the stomach. In turn, this may limit the amount of B12 available from food, but not from dietary supplements. Antacid abuse may also limit the absorption of B12.

Metaformin (Fortamet, Glucophage, Gluco-phage XR, Riomet), a drug used to treat diabetes, may indirectly decrease vitamin B12 absorption by altering calcium metabolism. When metaformin is taken for a long time (years), the risk of megaloblastic anemia and cardiovascular disease may increase.

Nitrous oxide (”laughing gas”) can inactivate the cobalamin form of vitamin B12. Nervous system symptoms can develop in people exposed to nitrous oxide if they already have with low vitamin B12 levels. This is unlikely to occur with people who have normal levels of B12.

Complications

No complications are expected from taking vitamin B12.

Parental concerns

Parents whose children are vegetarians should be concerned that they are getting enough vitamin B12. The nervous system grows rapidly in children and B12 is essential to its proper development. Nervous system damage caused by a lack of B12 is usually irreversible in children.

Resources

BOOKS

Berkson, Burt and Arthur J. Berkson. Basic Health Publications User's Guide to the B-complex Vitamins. Laguna Beach, CA: Basic Health Publications, 2006.

Gaby, Alan R., ed. A-Z Guide to Drug-Herb-Vitamin Interactions Revised and Expanded 2nd Edition: Improve Your Health and Avoid Side Effects When Using Common Medications and Natural Supplements Together. New York: Three Rivers Press, 2006.

Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007.

Pressman, Alan H. and Sheila Buff.The Complete Idiot's Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.

Rucker, Robert B., ed. Handbook of Vitamins. Boca Raton, FL: Taylor & Francis, 2007.

ORGANIZATIONS

Linus Pauling Institute. Oregon State University, 571 Weniger Hall, Corvallis, OR 97331–6512. Telephone: (541) 717–5075. Fax: (541) 737–5077. Website: <http://lpi.oregonstate.edu>

Office of Dietary Supplements, National Institutes of Health. 6100 Executive Blvd., Room 3B01, MSC 7517, Bethesda, MD 20892–7517 Telephone: (301)435–2920. Fax: (301)480–1845. Website: <http://dietary-supplements.info.nih.gov>

OTHER

Higdon, Jane. “Vitamin B12.”Linus Pauling Institute-Oregon State University, March 5, 2003. <http://lpi.oregonstate.edu/infocenter/vitamins/VitaminA>

Harvard School of Public Health. “Vitamins.” Harvard University, November 10, 2006. <http://www.hsph.harvard.edu/nutritionsource/vitamins.html>

Maryland Medical Center Programs Center for Integrative Medicine. “Vitamin B12 (Cobalamin).” University of Maryland Medical Center, April 2002. <http://www.umm.edu/altmed/ConsSupplements/VitaminB12Cobalamincs.html>

Medline Plus. “Vitamin B12.” U. S. National Library of Medicine, November 1, 2006. <http://www.nlm.nih/gov/medlineplus/druginfo/natural/patient-vitaminB12.html>

Office of Dietary Supplements.”Dietary Supplement Fact Sheet: Vitamin B12.” National Institutes of Health, April 26, 2006. <http://ods.od.nih.gov/factsheets/vitaminB12.asp>

Singh, Niranjan N. and Florian P. Thomas. “Vitamin B-12 Associated Neurological Diseases.” emedicine.com, July 18, 2006. <http://www.emedicine.com/med/topic439.htm>

Tish Davidson, A.M.

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Vitamin B12

Vitamin B12

Definition

Vitamin B12 is a water-soluble organic compound that the body needs to remain healthy. The only organisms that can make vitamin B12 are bacteria, fungi, yeast, molds, and algae. Humans must get it from foods in their diet . Vitamin B12 is sometimes called cobalamin.

Purpose

Vitamin B12 plays major roles in developing healthy red blood cells, creating new deoxyribose nucleic acid (DNA, genetic material), and in maintaining the health of nerve cells. It is also involved in making certain nutrients available to the body.

Description

Vitamin B12 is one of the least understood vitamins . Although some of its effects were experimentally discovered in the 1930s, Vitamin B12's structure was not determined until the 1960s. Questions still remain about some of its functions. Vitamin B12 is different from other vitamins in several ways. It is the only vitamin not made by any plant or animal, but only by microorganisms. It is the only vitamin to contain the metal cobalt (thus the name cobalamin), and it is the only vitamin that must combine with another substance, called the intrinsic factor (IF), before it can be absorbed by the body.

Although vitamin B12 is made only by microorganisms, it is found in association with animal protein. In nature, it comes in a variety of chemical forms that the body converts into two active forms of B12. Most B12dietary supplements contain the form called cyanocobalamin. B12 is included in over-the-counter multivitamins and in vitamin-B-complex supplements. It is also sold as a stand-alone dietary supplement and in an injectable form available only by prescription.

When people eat animal protein-beef, fish, pork, chicken, eggs, milk, cheese-the stomach is stimulated to secrete hydrochloric acid and enzymes that break down the protein and release vitamin B12. B12 then binds with IF, which is made in the stomach. Vitamin B12 cannot be absorbed into the body unless it is combined with IF. Therefore, either an absence of B12 in diet or inability of the stomach to make IF can result in B12 deficiency.

Some fermented bean products such as tofu, tempeh, natto, tamari, and miso may or may not contain vitamin B12 depending on which bacteria were used to ferment these products. Nutritional yeast also may or may not contain vitamin B12 depending on the type of yeast used. Consumers should read labels of these products carefully. The best source of vitamin B12 for people who do not eat meat or animal products is fortified breakfast cereal. Cereals can be fortified at various strengths, ranging from in amounts ranging from 100% of the daily requirement to 25% of the daily requirement. The label must contain information about vitamin fortification.

KEY TERMS

Amino acid —Molecules that are the basic building blocks of proteins.

Dietary supplement —A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual's diet with the expectation that it will improve health.

Enzyme —A protein that change the rate of a chemical reaction within the body without themselves being used up in the reaction.

Vitamin —A nutrient that the body needs in small amounts to remain healthy but that the body cannot manufacture for itself and must acquire through diet.

Water-soluble vitamin —A vitamin that dissolves in water and can be removed from the body in urine.

Vitamin B12's role in health

Vitamin B12 is crucial to the development of healthy red blood cells. As red blood cells mature, they need new DNA. In the absence of adequate vitamin B12, the new DNA is defective. This results in red blood cells that are too large and poorly shaped. These malformed cells have a reduced ability to carry oxygen and result in pernicious anemia or megaloblastic anemia.

Vitamin B12 also is necessary to maintain healthy nerves. Nerves are covered with a fatty sheath called myelin. The myelin covering is necessary for effective transmission of nerve impulses. When vitamin B12 is absent, the myelin sheath does not form correctly.

Proteins in the diet are broken down into small molecules called amino acids that are then used by the body to build new proteins. Vitamin B12 helps make amino acid available to the body. High levels of one particular amino acid, homocysteine, are associated with increased risk of heart disease . Vitamin B12, along with vitamin B6 and folic acid help reduce the level of homocysteine in the blood. Vitamin B12 is also thought to play a role in making carbohydrates and fats available to the body. Clinical trials are underway to determine safety and effectiveness of vitamin B12 in a variety of situations. Individuals interested in participating in a clinical trial at no charge can find a list of open trials at http://www.clinicaltrials.gov.

Normal vitamin B12 requirements

The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97–98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects.

The following are the RDAs and IAs for vitamin B12 for healthy individuals:

  • people 14 years and older: RDA 2.4 mcg

Sources of vitamin B12

Vitamin B12 is found in food that comes from animals, including meat, fish, poultry, eggs, milk, and cheese. It is also added to fortified breakfast cereals and is found in some fermented bean products. Heating or cooking foods does not reduce their vitamin B12 content very much.

The following list gives the approximate vitamin B12 content for some common foods:

  • calf's liver, cooked, 4 ounces: 41 mcg
  • salmon, baked or broiled, 4 ounces: 3.3 mcg
  • shrimp, steamed or boiled, 4 ounces: 1.7 mcg
  • mollusks or clams, cooked, 3 ounces: 84 mcg
  • tuna, white, canned in water, 3 ounces: 1.0 mcg
  • beef, top sirloin, broiled, 3 ounces: 2.4 mcg
  • cheeseburger, fast food, double patty: 1.9 mcg
  • taco, fast food, 1 large: 1.6 mcg
  • ham, canned or roasted, 3 ounces: 0.6 mcg
  • chicken breast, roasted, 1/2 breast: 0.3mcgl milk, 1 cup: 0.9 mcg
  • egg, 1 whole, cooked: 0.3 mcg
  • breakfast cereal, fortified 100%, 3/4 cup: 6.0 mcg
  • breakfast cereal, fortified 25%, 3/4 cup: 1.5 mcg

Vitamin B12 deficiency

Vitamin B12 deficiency is hard to determine, and there is little agreement on how many people are vitamin B12 deficient. This is partly because the body can store 5–10 year's worth of vitamin B12, so symptoms of deficiency are slow to show up, especially in adults. Researchers estimate that anywhere from 300,000–3 million Americans are vitamin B12 deficient.

Most meat-eating Americans get enough vitamin B12 from diet alone. However, the elderly are at higher risk than younger people of developing mild vitamin B12 deficiency. Other people at greater risk of vitamin B12 deficiency include:

  • vegans who eat no animal products
  • people who have had part of their stomach or intestine removed
  • people with diseases that interfere with the absorption of nutrients such as Crohn's disease, celiac disease, or ulcerative colitis.
  • people with alcoholism
  • people with liver or kidney damage
  • people with HIV/AIDS

Symptoms of vitamin B12 deficiency include shaky movements, loss of balance, muscle weakness and spasms, vision problems, reduced mental functioning, and changes in mood and mental state. These symptoms are quite general and have many other causes besides vitamin B12 deficiency.

Precautions

Individuals with the eye disorder Leber's optic atrophy should not use vitamin B12 supplements. High levels of B12 will accelerate degeneration of the optic nerve, leading to blindness. Folic acid may mask vitamin B12 deficiency.

Folic acid supplements will reverse anemia symptoms, but they do not stop nerve damage caused by B12 deficiency. Permanent nerve damage may result.

People with suspected folic acid deficiency who begin taking folic acid supplements should also be evaluated for vitamin B12 deficiency.

Interactions

Many drugs used to treat gastroesophageal reflux disease (GERD) such as omeprazole (Prilosec), lansoprazole (Prevacid), cimetidine (Tagamet), famotidine (Pepsid), nizatidine (Axid), or ranitidine (Zantac) decrease the amount of hydrochloric acid secreted by the stomach. In turn, this may limit the amount of B12available from food, but not from dietary supplements. Antacid abuse may also limit the absorption of B12.

Metaformin (Fortamet, Glucophage, Glucoph-age XR, Riomet), a drug used to treat diabetes, may indirectly decrease vitamin B12 absorption by altering calcium metabolism. When metaformin is taken for a long time (years), the risk of megaloblastic anemia and cardiovascular disease may increase.

Nitrous oxide (“laughing gas”) can inactivate the cobalamin form of vitamin B12. Nervous system symptoms can develop in people exposed to nitrous oxide if they already have with low vitamin B12 levels. This is unlikely to occur with people who have normal levels of B12. Complications No complications are expected from taking vitamin B12.

Resources

BOOKS

Berkson, Burt and Arthur J. Berkson. Basic Health Publications User's Guide to the B-complex Vitamins. Laguna Beach, CA: Basic Health Publications, 2006.

Gaby, Alan R., ed. A-Z Guide to Drug-Herb-Vitamin Interactions Revised and Expanded 2nd Edition: Improve Your Health and Avoid Side Effects When Using Common Medications and Natural Supplements Together. New York: Three Rivers Press, 2006.

Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.

Rucker, Robert B., ed. Handbook of Vitamins. Boca Raton, FL: Taylor & Francis, 2007.

Tish Davidson A.M.

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"Vitamin B12." The Gale Encyclopedia of Senior Health: A Guide for Seniors and Their Caregivers. . Retrieved September 20, 2018 from Encyclopedia.com: http://www.encyclopedia.com/caregiving/encyclopedias-almanacs-transcripts-and-maps/vitamin-b12

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Vitamin B12

Vitamin B12

Description

Cobalamin, also known as B12, is a member of the water-soluble family of B vitamins . It is a key factor in the body's proper use of iron and formation of red blood cells. The nervous system also relies on an adequate supply of cobalamin to function appropriately, as it is an essential component in the creation and maintenance of the myelin sheath that lines nerve cells. Other roles of cobalamin include working with pyridoxine (vitamin B6 and folic acid to reduce harmful homocysteine levels, participating in the metabolization of food, and keeping the immune system operating smoothly.

General use

Very small amounts of cobalamin are needed to maintain good health. The RDA value is 0.3 micrograms (mcg) for infants under six months, 0.5 mcg for those six months to one year old, 0.7 mcg for children one to three years old, 1.0 mcg for children four to six years old, 1.4 mcg for children seven to 10 years old, and 2 mcg for those 11 years of age and older. Requirements are slightly higher for pregnant (2.2 mcg) and lactating (2.6 mcg) women.

The primary conditions that benefit from supplementation with cobalamin are megaloblastic and pernicious anemia. Megaloblastic anemia is a state resulting from an inadequate intake of cobalamin, to which vegans are particularly susceptible because of the lack of animal food sources. Vegans, who do not consume any animal products including meat, dairy, or eggs, should take at least 2 mcg of cobalamin per day in order to prevent this condition. In the case of pernicious anemia, intake may be appropriate but absorption is poor due to a lack of normal stomach substance, called intrinsic factor, that facilitates absorption of vitamin B12. Large doses are required to treat pernicious anemia, which occurs most commonly in the elderly population as a result of decreased production of intrinsic factor by the stomach. Supplements are generally effective when taken orally in very large amounts (300-1000 mcg/day) even if no intrinsic factor is produced. These supplements require a prescription, and should be administered with the guidance of a health care provider. Injections, instead of the supplements, are often used.

Those who have infections, burns , some types of cancer , recent surgery, illnesses that cause decay or loss of strength, or high amounts of stress may need more than the RDA amount of B12 and other B vitamins. A balanced supplement is the best approach.


KEY TERMS


Homocysteine —An amino acid produced from the metabolization of other amino acids. High levels are an independent risk factor for heart disease.

Megaloblastic anemia —A condition caused by cobalamin deficiency, which is characterized by red blood cells which are too few, too fragile, and abnormally large. Also known as macrocytic anemia.

Pernicious anemia —Megaloblastic anemia resulting from a cobalamin deficiency that is the result of poor absorption due to inadequate production of intrinsic factor in the stomach.

Vegan —A person who doesn't eat any animal products, including dairy and eggs.


Male infertility can sometimes be resolved through use of cobalamin supplements. Other conditions that may be improved by cobalamin supplementation include: asthma , atherosclerosis (hardening of the arteries caused by plaque formation in the arteries), bursitis (inflammation of a bodily pouch, especially the shoulder or elbow), Crohn's disease (chronic recurrent inflammation of the intestines), depression, diabetes, high cholesterol, osteoporosis , and vitiligo (milky-white patches on the skin). There is not enough evidence to judge whether supplementation for these diseases is effective.

Preparations

Natural sources

Usable cobalamin is only found naturally in animal source foods. Fresh food is best, as freezing and exposure to light may destroy some of the vitamin content. Clams and beef liver have very high cobalamin levels. Other good sources include chicken liver, beef, lamb, tuna, flounder, liverwurst, eggs, and dairy products. Some plant foods may contain cobalamin, but it is not in a form that is usable by the body.

Supplemental sources

Cobalamin supplements are available in both oral and injectable formulations. A nasal gel is also made. Generally a balanced B-complex vitamin is preferable to taking high doses of cobalamin unless there is a specific indication for it, such as megaloblastic anemia. Strict vegetarians will need to incorporate a supplemental source of B12 in the diet. Cyanocobalamin is the form most commonly available in supplements. Two other, possibly more effective, types are hydrocobalamin and methyl-cobalamin. As with all supplements, cobalamin should be stored in a cool, dry, dark place and out of the reach of children.

Deficiency

Cobalamin deficiency may be manifested as a variety of symptoms since cobalamin is so widely used in the body. Severe fatigue may occur initially. Effects on the nervous system can be wide-ranging, and include weakness, numbness and tingling of the limbs, memory loss, confusion, delusion, poor balance and reflexes , hearing difficulties, and even dementia . Severe deficiency may appear similar to multiple sclerosis . Nausea and diarrhea are possible gastrointestinal signs. The anemia that results from prolonged deficiency may also be seen as a pallor, especially in mucous membranes such as the gums and the lining of the inner surface of the eye.

Megaloblastic anemia is a common result of inadequate cobalamin. This condition can also result if a person stops secreting enough intrinsic factor in the stomach, a substance essential for the absorption of cobalamin. Inadequate intrinsic factor leads to pernicious anemia, so called because it persists despite iron supplementation. Long-term deficiencies of cobalamin also allow homocysteine levels to build up. Negative effects of large amounts of circulating homocysteine include heart disease, and possibly brain toxicity. Taking high levels of folic acid supplements can mask cobalamin deficiency and prevent the development of megaloblastic anemia, but neurological damage can still occur. This damage may become permanent if the cobalamin deficiency persists for a long period of time.

Risk factors for deficiency

The primary groups at risk for cobalamin deficiency are vegans who are not taking supplements, and the elderly. Older adults are more likely to have both insufficient intrinsic factor secreted by the stomach and low levels of stomach acid, causing cobalamin to be poorly absorbed. Malabsorptive diseases and stomach surgery can also predispose to a deficiency.

Precautions

People who are sensitive to cobalamin or cobalt should not take cobalamin supplements. Symptoms of hypersensitivity may include swelling, itching, and shock . Adverse effects resulting from B12 supplementation are rare. Cobalamin should also be avoided by those who have a type of hereditary optic nerve atrophy known as Leber's disease.

Side effects

Very high doses of cobalamin may sometimes cause acne.

Interactions

Large amounts of vitamin C taken within an hour of vitamin B supplements will destroy the cobalamin component. Absorption of cobalamin is also impaired by deficiencies of folic acid, iron, or vitamin E . Improved absorption occurs when it is taken with other B vitamins or calcium . Some medications may also cause an increased use or decreased absorption of this vitamin. Those on colchicine, corticosteroids , methotrexate, metformin, phenformin, oral contraceptives, cholestyramine, colestipol, clofibrate, epoetin, neomycin, or supplemental potassium may need extra cobalamin. Use of nicotine products or excessive alcohol can deplete B12.

Resources

BOOKS

Bratman, Steven, and David Kroll. Natural Health Bible. CA: Prima Publishing, 1999.

Feinstein, Alice. Prevention's Healing with Vitamins. PA: Rodale Press, 1996.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: The Complete Guide. AZ: Fisher Books, 1998.

Jellin, Jeff, Forrest Batz, and Kathy Hitchens. Pharmacist's Letter/Prescriber's Letter Natural Medicines Comprehensive Database. CA: Therapeutic Research Faculty, 1999.

Pressman, Alan H. and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. New York: Alpha Books, 1997.

Judith Turner

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