What is Vitamin B12?
Vitamin B12 is needed to produce an adequate amount of healthy red blood cells in the bone marrow. Vitamin B12 is available only in animal foods (meat and dairy products) or yeast extracts.
B12 deficiency is defined by low levels of stored B12 in the body that can result in anaemia.
- Absence of intrinsic factor, also called pernicious anaemia — Intrinsic factor is a protein secreted by cells of the stomach lining. Intrinsic factor attaches to vitamin B12 and takes it to the intestines to be absorbed. An absence of intrinsic factor is the most common cause of pernicious anaemia. Absent intrinsic factor is often associated with a condition called atrophic gastritis, a thinning of the lining of the stomach. Atrophic gastritis is more common in elderly people of African-American or Northern-European descent. In these people, pernicious anaemia develops at about age 60.
Pernicious anaemia occurs more commonly in people who already have diseases that are linked to immune-system abnormalities, such as Graves’ disease, hypothyroidism (under-functioning thyroid gland), thyroiditis (inflammation of the thyroid), vitiligo and Addison’s disease (adrenocortical insufficiency).
- Removal or destruction of the stomach — Vitamin B12 deficiency can develop in people who have had surgery to remove part or all of the stomach.
- Overgrowth of bacteria — Some people develop vitamin B12 deficiency as a result of conditions that slow the movement of food through the intestines (diabetes, scleroderma, strictures, diverticula), allowing intestinal bacteria to multiply and overgrow in the upper part of the small intestine. These bacteria steal B12 for their own use, rather than allowing it to be absorbed by the body.
- Dietary deficiency — Vegans (strict vegetarians who do not eat any meat, fish, egg or dairy products) can develop vitamin B12 deficiency because they lack vitamin B12 in their diets. In patients with bulimia or anorexia nervosa, vitamin B12 deficiency also can be related to diet. However, your liver can store vitamin B12 for up to five years, so it’s rare for a diet to cause this anaemia.
Symptoms tend to develop slowly and may not be recognized immediately. As the condition worsens, common symptoms include:
- Weakness and fatigue
- Light-headedness and dizziness
- Palpitations and rapid heartbeat
- Shortness of breath
- A sore tongue that has a red, beefy appearance
- Nausea or poor appetite
- Weight loss
- Yellowish tinge to the skin and eyes
If low levels of B12 remain for a long time, the condition also can lead to irreversible damage to nerve cells, which can cause the following symptoms:
- Numbness and tingling in the hands and feet
- Difficulty walking
- Muscle weakness
- Memory loss
Tests will include:
- Standard blood tests to measure the level of red blood cells and check their appearance — In vitamin B12 deficiency, red blood cells are unusually large and appear abnormal.
- Blood tests to measure B12 levels — Levels of iron and folate also may be measured to check for deficiencies in these nutrients.
- Blood test to measure methylmalonic acid level — The blood level of methylmalonic acid increases when a person has B12 deficiency.
- Blood tests for intrinsic factor antibody — Your doctor may order special tests for antibody levels to determine if you have pernicious anaemia. Most people who lack intrinsic factor in their stomach have these antibodies in their blood.
Treatment for this condition involves replacing the missing vitamin B12. People who cannot absorb B12 need regular injections. When injections first are administered, a patient with severe symptoms may receive six during the first 2 weeks to restore the body’s reserves of this nutrient. A response usually is seen within 48 to 72 hours, with brisk production of new red blood cells. Once B12 reserves reach normal levels, injections of vitamin B12 will be needed every one to three months to prevent symptoms from returning. People who cannot absorb vitamin B12 should continue to eat a well-balanced diet that provides other nutrients (folic acid, iron and vitamin C) necessary to produce healthy blood cells. Sometimes people can take high doses of oral B12 to provide replacement instead of undergoing injections, but a physician should closely supervise this.
In people whose vitamin B12 deficiency is related to overgrowth of intestinal bacteria, treatment with oral antibiotics, such as tetracycline (sold under several brand names), may stop bacterial overgrowth and allow the absorption of vitamin B12 to return to normal.
Vitamin B12 deficiency resulting from inadequate dietary intake is the easiest to treat. The condition can be reversed by taking oral vitamin B12 supplements and adding foods containing B12.
The outlook is excellent because this form of anaemia responds well to treatment. However, it is possible that nerve cell damage will be permanent. Some residual damage to the nervous system may remain in people who sought treatment late in the illness.
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