Vitamin B12 - General Information, Uses & Deficiencies
General Information, Uses & Deficiencies
Vitamin B12, which is also known as cobalamin, was the last B vitamin to be identified. It is water soluble, bright red in color and has an atom of cobalt at its center. The average adult body contains 2 to 5 mg of vitamin B12, with 80 per cent of this stored in the liver.
What it does in the body
Vitamin B12 is essential for metabolism of fats and carbohydrates and the synthesis of proteins. Vitamin B12 is also essential for the transport and storage of folate in cells and for conversion to its active form. Rapidly dividing cells, such as those in the epithelium and bone marrow, have the greatest need for vitamin B12.
Brain and nervous system
Vitamin B12 is involved in the manufacture of the myelin sheath, a fatty layer which insulates nerves. It is also essential in the formation of neurotransmitters.
The manufacture and normal functioning of blood cells requires vitamin B12.
Vitamin B12 is necessary for the production of nucleic acids, which make up DNA, the genetic material of the cell.
Absorption and metabolism
A compound known as intrinsic factor which is secreted by the cells lining the stomach is necessary for absorption of vitamin B12 from the small intestine. Those with malabsorption problems; such as celiac disease, low stomach acid, or who have had stomach or intestinal surgery; may have problems absorbing vitamin B12. Calcium and iron assist with vitamin B12 absorption.
Vitamin B12 is bound to proteins known as transcobalamins in the blood. It is excreted in the bile and re-absorbed. Those on diets which are low in vitamin B12 may obtain more from re-absorption than from food. Because of this re-absorption, vitamin B12 deficiency can take many years to become apparent.
The Schilling test, which uses a small dose of radioactive vitamin B12 and then a larger dose of normal B12 to flush this out, is used to measure the ability of a person to absorb vitamin B12.
As the body stores vitamin B12, symptoms of deficiency can take up to four to five years of poor dietary intake or lack of intrinsic factor production to appear. Deficiency is more commonly linked to the inability to absorb the vitamin due to lack of intrinsic factor than to insufficient dietary intake.
Vitamin B12 deficiency is more common in the elderly than in younger people, with around 15 per cent of elderly men and women affected. This is usually because of decreased absorption due to reduced production of intrinsic factor or to a stomach disorder known as atrophic gastritis. Supplementation can prevent irreversible neurological damage if started early. Elderly people with vitamin B12 deficiency may show psychiatric or metabolic deficiency symptoms even before anemia is diagnosed. Screening for low vitamin B12 levels is necessary in elderly people with mental impairment, although it has also been found that deficiency states can still exist even when blood levels are higher than the traditional lower reference limit for vitamin B12. patients who are most at risk of vitamin B12 deficiency include those with gastrointestinal disorders, autoimmune disorders, Type I diabetes mellitus and thyroid disorders, and those receiving long-term therapy with gastric acid inhibitors.1
Vitamin B12 deficiency causes pernicious anemia with symptoms of tiredness, pallor, lightheadedness, breathlessness, headache and irritability. Red blood cells become abnormally enlarged and reduced blood platelet formation causes poor clotting and bruising. A high intake of folic acid can prevent the red blood cell changes caused by vitamin B12 deficiency. It does not, however, prevent the nerve damage which may only become apparent in later stages and which may not be reversible. Strict vegetarians, whose folic acid intakes are high while their vitamin B12 intakes are low, may be at particular risk of nerve damage.
Vitamin B12 deficiency leads to reduced numbers of white blood cells which causes increased susceptibility to infection. Recent research has shown that elderly patients with low vitamin B12 levels have impaired antibody response to bacterial vaccine, even when there are no clinical signs of deficiency.2
Brain and nervous system
Vitamin B12 deficiency eventually leads to a deterioration in mental functioning, to neurological damage and to a number of psychological disturbances including memory loss, disorientation, dementia, moodiness, confusion and delusions. Alzheimer's disease sufferers are often found to have low vitamin B12 levels, although it is unclear whether these are a contributing factor or a result of the disease.
Vitamin B12 deficiency leads to a loss of nerve-insulating myelin which begins at the peripheral nerves and eventually moves up to the spine causing decreased reflexes, abnormal gait, weakness, fatigue, poor vision and impaired touch or pain sensation. Other signs include tingling or loss of sensation and weakness in hands and feet, and diminished sensitivity to vibration and position sense.
Vitamin B12 deficiency causes poor cell formation in the digestive tract and leads to nausea, vomiting, loss of appetite, poor absorption of food, soreness of the mouth and tongue, and diarrhea.
Vitamin B12 deficiency may lead to increased levels of an amino acid called homocysteine, which has been linked to an increased risk of heart disease.3
Vitamin B12 is involved in production of the genetic material of the cell and deficiency may cause defective production which could lead to cancer. A 1997 Australian study found that low levels of vitamin B12 could contribute to chromosome damage in white blood cells.4 Low levels of Vitamin B12 may also contribute to diabetic neuropathy, poor vision, recurrent yeast infections and infertility. Vitamin B12 affects bone cells, and deficiency may be risk factor for osteoporosis.5
Good sources of vitamin B12 include liver and organ meats, muscle meats, fish, eggs, shellfish, milk and most dairy products. Sea vegetables and fermented soybean products such as miso also contain forms of vitamin B12, although some research suggests that the human body may not be able to absorb these forms and they may even block true vitamin B12 absorption. Many vegetarian and vegan products are fortified with vitamin B12, including yeast extract, vegetable stock and soya milk. Cooking has little effect on vitamin B12 although some may be lost when food is cooked to temperatures above 212 degrees F.
Beef liver, cooked 85g 95.0 mg
Beef kidney, cooked 85g 43.6 mg
Trout, cooked 1 fillet 4.64 mg
Tuna, canned, 1 cup 4.38 mg
pink salmon, cooked fillet 4.29 mg
Beef steak, grilled 100g 2.11 mg
Haddock, cooked 1 fillet 2.08 mg
Tempeh 1 cup 1.58 mg
Cottage cheese 1 cup 1.36 mg
Clams cup 1.05 mg
Oysters 6 oysters 1.02 mg
Cheeseburger 1 serve 0.97 mg
Skim milk 1 cup 0.88 mg
Whole milk plain yoghurt 1 cup 0.86 mg
Whole milk 1 cup 0.83 mg
Feta cheese 1 wedge 0.64 mg
Miso 1 cup 0.54 mg
Eggs, hard boiled 1 large 0.56 mg
Eggs, scrambled 1 large 0.47 mg
Chicken, roast 1 cup, chopped 0.44 mg
Eggs, omelette 1 large 0.43 mg
Breaded fried chicken 6 pieces 0.31 mg
Cheddar cheese 1 slice 0.23 mg
Ham 1 slice 0.23 mg
Recommended dietary allowances
The RDAs for vitamin B12 have recently been raised in the US.
Men 2.4 mcg
Women 2.4 mcg
pregnancy 2.6 mcg
Lactation 2.8 mcg
Men 1.5 mcg
Women 1.5 mcg
pregnancy 2.0 mcg
Men 2.0 mcg
Women 2.0 mcg
pregnancy 3.0 mcg
Lactation 2.5 mcg
Vitamin B12 is available in several supplemental forms, both oral and injectable. Cyanocobalamin is the main synthetic form and has a cyanide molecule attached. Methylcobalamin is one of two active forms of vitamin B12 and may be a more effective supplement.
Vegans are at particular risk of vitamin B12 deficiency and may need supplements. Vitamin B12 tablets should be taken one hour before food for optimal absorption.
Toxic effects of excess intake
There have been no reports of toxic effects even at high doses.
Therapeutic uses of supplements
Both oral and injectable vitamin B12 supplements are used to treat pernicious anemia. In those who lack sufficient intrinsic factor and cannot absorb vitamin B12, it is usually given by injection, although there is evidence that oral administration in high enough doses is effective.6 An intranasal gel is also available.
Lower than normal serum vitamin B12 levels are common in those infected with HIV and may help predict those patients in whom the disease will progress most rapidly.7 AIDS patients often show signs of nerve damage including numbness and tingling in the hands and toes, and vitamin B12 may be useful in treating these symptoms. Recent studies have found that deficiency of vitamin B12 is associated with lower measures of immune system effectiveness in HIV-positive people and that increasing vitamin B12 levels increases these counts.8,9
Some research suggests that vitamin B12 might affect sleep quality and performance. In a 1996 study, researchers explored the effects of 3 mg of vitamin B12 on the quality of sleep and work performance of ten healthy, male staff members of an Austrian industrial plant. The results showed better sleep quality and shorter total sleep time in those taking supplements.10
Vitamin B12 therapy has also been used to treat Alzheimer's disease, childhood asthma in those sensitive to sulfites, insomnia, diabetic neuropathy, some psychiatric disorders including depression, and some forms of dermatitis.
Vitamin B12 injections are used by some people as a general tonic and many people report feelings of increased energy and improved health after these injections. Between 70 and 90 per cent of any dose over 1 mg is excreted into the urine.
Interactions with other nutrients
Vitamin B12 works closely with folic acid and vitamin B6 in a number of body functions. Vitamin B6 deficiency reduces vitamin B12 absorption.
Interactions with drugs
Acids and alkalis, water, sunlight, alcohol, estrogen and sleeping pills can destroy vitamin B12. Antacids, anti-epileptic drugs, cholestyramine and colchicine may decrease vitamin B12 absorption. Chloramphenicol and other bone marrow suppressant drugs may interfere with the red blood cell functions of vitamin B12. Smoking affects vitamin B12 metabolism.
The clinically available cyanocobalamin form of vitamin B12 should not be used in patients with hereditary optic nerve atrophy or suspected cobalt hypersensitivity. Large doses of vitamin B12 should be used with caution in those with low blood levels of potassium (due to diuretic drugs or other causes).
- Nilsson Ehle H Age-related changes in cobalamin (vitamin B12) handling. Implications for therapy. Drugs Aging, 1998 Apr, 12:4, 277-92
- Fata FT; Herzlich BC; Schiffman G; Ast AL. Impaired antibody responses to pneumococcal polysaccharide in elderly patients with low serum vitamin B12 levels. Ann Intern Med, 1996 Feb, 124:3, 299-304
- Chadefaux B; Cooper BA; Gilfix BM; Lue Shing H; Carson W; Gavsie A; Rosenblatt DS. Homocysteine: relationship to serum cobalamin, serum folate, erythrocyte folate, and lobation of neutrophils. Clin Invest Med, 1994 Dec, 17:6, 540-50
- Fenech MF; Dreosti IE; Rinaldi JR. Folate, vitamin B12, homocysteine status and chromosome damage rate in lymphocytes of older men. Carcinogenesis, 1997 Jul, 18:7, 1329-36
- Kim GS; Kim CH; park JY; Lee KU; park CS Effects of vitamin B12 on cell proliferation and cellular alkaline phosphatase activity in human bone marrow stromal osteoprogenitor cells and UMR106 osteoblastic cells. Metabolism, 1996 Dec, 45:12, 1443-6
- Lederly FA. Oral cobalamin for pernicious anemia: Medicine's best kept secret. JAMA. 1991;265:94,95
- Tang AM; Graham NM; Chandra RK; Saah AJ. Low serum vitamin B-12 concentrations are associated with faster human immunodeficiency virus type 1 (HIV-1) disease progression. J Nutr, 1997 Feb, 127:2, 345-51
- Kieburtz KD; Giang DW; Schiffer RB; Vakil N. Abnormal vitamin B12 metabolism in human immunodeficiency virus infection. Association with neurological dysfunction. Arch Neurol, 1991 Mar, 48:3, 312-4
- Baum MK; Beach R; Morgan R; Mantero-Atienza A; Wilke F; Eisdorfer C. Vitamin B12 and cognitive function in HIV infection. Int Conf AIDS, 1990 Jun 20-23, 6:2, 97 (abstract no. F.B.32)
- Bohr KC. Effect of vitamin B12 on sleep quality and performance of shift workers. Wien Med Wochenschr, 1996, 146:13-14, 289-9