Cynocobalamine deficiency.,
Intrinsic Factor deficiency
Intrinsic factor may be lacking because abnormal antibodies, produced by an overactive immune system, attack and destroy the stomach cells that produce intrinsic factor- an autoimmune reaction. Intrinsic factor may be lacking because the part of the stomach where it is produced was surgically removed. Vitamin B12 deficiency due to lack of intrinsic factor causes a type of anemia called pernicious anemia.
Among older people, absorption may be inadequate because stomach acidity is decreased. Decreased stomach acidity reduces the body's ability to remove vitamin B12 from the protein in meat. The vitamin B12 found in vitamin supplements, however, can continue to be well absorbed even in people with decreased stomach acid.
Inadequate storage:
Liver disorders may interfere with the storage of vitamin B12.
Symptoms of B-12 deficiency
Anemia due to vitamin B12 deficiency develops gradually, allowing the body to adapt somewhat. Consequently, symptoms may be mild even when anemia is severe. Symptoms of anemia are paleness, weakness, and fatigue. If severe, anemia causes shortness of breath, dizziness, and a rapid heart rate. Occasionally, the spleen and liver enlarge. Younger adults who have pernicious anemia (due to lack of intrinsic factor) are more likely to develop stomach and other gastrointestinal cancers.
In people with nerve damage, the legs are affected earlier and more often than the arms. Tingling is felt in the feet and hands, and sensation in the legs, feet, and hands is lost. People become less able to tell where their arms and legs are (position sense) and to feel vibrations. Mild to moderate muscle weakness develops, and reflexes may be lost. Walking becomes difficult. Some people become confused, irritable, and mildly depressed. Advanced vitamin B12 deficiency may lead to delirium, paranoia, and impaired mental function, including dementia.
Diagnosis of B-12 deficiency
Usually, vitamin B12 deficiency is suspected when routine blood tests detect large red blood cells. If the deficiency is suspected, the level of vitamin B12 in the blood is measured. Usually, doctors also measure the blood level of folate to rule out folate deficiency, which can also result in large red blood cells.
If vitamin B12 deficiency is confirmed in an older person, no other tests are done because the cause, such as low stomach acidity, is usually not serious. In a younger person, other tests, including other blood tests, may be done to determine the cause. These tests (including the Schilling test) usually focus on intrinsic factor. Endoscopy (use of a flexible viewing tube to directly examine a body cavity) may be done to check for destruction of stomach cells that produce intrinsic factor.
Prevention and Treatment of B-12 deficiency
Giving infants of vegan mothers vitamin B12 supplements from birth helps prevent the deficiency.
Older people with vitamin B12 deficiency benefit from taking vitamin B12 supplements because the deficiency usually results from difficulty absorbing the vitamin from meat. They can absorb the vitamin more easily from supplements than from meat.
Treatment of vitamin B12 deficiency or pernicious anemia consists of high doses of vitamin B12 supplements. If people have the deficiency but no symptoms, the vitamin may be taken by mouth. Blood tests are done periodically to make sure the vitamin B12 level returns to and remains normal. People who have symptoms due to nerve damage are usually given vitamin B12 by injection into a muscle. Injections, which may be self-administered, are given daily or weekly for several weeks until the vitamin B12 level returns to normal. Then injections are given once a month indefinitely, unless the disorder causing it can be corrected. Anemia usually resolves in about 6 weeks. But severe symptoms due to nerve damage- for example, dementia in older people- may not resolve
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