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MULTIPLE SCLEROSIS
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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 Metabolism 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. Blood cells The manufacture and normal functioning of
blood cells requires vitamin B12. Genetic material 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. Deficiency 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. Elderly people 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
Blood 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. Immune system 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. Gastrointestinal system 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. Heart disease 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 Other symptoms 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 Sources 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 ½ 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 ¾ 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. USA Men 2.4 mcg Women 2.4 mcg Pregnancy 2.6 mcg Lactation 2.8 mcg UK Men 1.5 mcg Women 1.5 mcg Pregnancy 2.0 mcg Lactation Australia Men 2.0 mcg Women 2.0 mcg Pregnancy 3.0 mcg Lactation 2.5 mcg Supplements 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 Pernicious anemia 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. HIV / AIDS 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 Sleep 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
Other uses 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. Cautions 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).
Copyright Bookman Press
1998 |
