Vitamin B12 Deficiency

What Is It?

Vitamin B12, available only in animal foods (meat and dairy products) or yeast extracts (such as brewer’s yeast) is needed to produce an adequate amount of healthy red blood cells in the bone marrow. Vitamin B12 deficiency is defined by low levels of stored B12 in the body that can result in anemia, a lower-than-normal number of red blood cells.

Vitamin B12 deficiency can develop for the following reasons:

  • Absence of intrinsic factor (IF), also called pernicious anemia — IF is a protein secreted by cells of the stomach lining. IF attaches to vitamin B12 and takes it to the intestines to be absorbed. An absence of IF is the most common cause of pernicious anemia, and it typically causes the stomach lining to shrink (atrophy). This condition often is seen in elderly people of African-American or Northern-European descent. In these patients, pernicious anemia develops at about age 60, and men and women are affected equally. In children, decreased levels of IF can be an inherited (genetic) condition. When this happens, low levels of IF produce symptoms of juvenile pernicious anemia in patients younger than age 10. Pernicious anemia 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 patients 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 dietary causes of this anemia are rare.


Symptoms tend to develop slowly and may not be recognized immediately. As the condition worsens, common symptoms can include:

  • Weakness and fatigue
  • Lightheadedness and dizziness
  • Palpitations and rapid heartbeat
  • Shortness of breath
  • Bleeding gums and mouth sores
  • A sore tongue that has a red, beefy appearance
  • Nausea or poor appetite
  • Weight loss
  • Diarrhea
  • Yellowish tinge to the skin and eyes

If low levels of B12 remain for a long time, the condition also can lead to irreversible nerve-cell damage, producing the following symptoms:

  • Numbness and tingling in the hands and feet
  • Difficulty walking
  • Muscle weakness
  • Irritability
  • Memory loss
  • Dementia
  • Depression
  • Psychosis


Your doctor will ask you about your diet and about any family history of anemia. Your doctor also will review your medical history for medical illnesses (diabetes, immune disorders) or surgeries (such as stomach removal) that can lead to B12 deficiency.

Your doctor may suspect that you have vitamin B12 deficiency based on your medical history and symptoms. To confirm the diagnosis, he or she will perform a physical examination and order laboratory tests. During the physical examination, your doctor will look for a red, beefy tongue, pale or yellowish skin, a rapid pulse, and heart murmurs resulting from an anemia-related increase in blood flow demands on the heart. Laboratory 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 have an abnormal appearance.
  • 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 (IF) antibody and parietal cell antibody levels — If B12 and methylmalonic acid levels are low, your doctor may order special tests for antibody levels to determine if you have pernicious anemia. Most people who lack IF in their stomach have these antibodies in their blood.
  • Bone-marrow biopsy — Occasionally, a bone-marrow biopsy is performed to help confirm the diagnosis. In this procedure, a small sample of bone marrow is taken by inserting a needle into the pelvic bone just below the waist on either side of the spine. The bone-marrow sample is examined in a laboratory to help rule out other causes of anemia and red-cell abnormalities.

Expected Duration

With proper treatment, symptoms of vitamin B12 deficiency begin to improve within a few days. In vegans and other people whose B12 deficiency is diet-related, oral B12 supplements and a diet designed to increase consumption of vitamin B12 should cure the condition. People with pernicious anemia or people who cannot absorb vitamin B12 from their intestines will need injections of vitamin B12 every one to three months indefinitely.


To prevent vitamin B12 deficiency, vegans should take adequate amounts of vitamin B12 supplements to make up for their dietary shortage.

For people who cannot absorb B12, the condition is not preventable. However, once it is diagnosed, regular injections of vitamin B12 will prevent symptoms from recurring.


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 five to seven during the first week 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, lifelong therapy, with vitamin B12 injections every one to three months, is needed to prevent symptoms from recurring in people whose vitamin B12 deficiency is not diet-related. For these patients, oral supplements and dietary changes usually do not work to raise B12 levels. However, these patients should continue to eat a well-balanced diet that provides other nutrients (folic acid, iron and vitamin C) necessary for healthy blood-cell production. Sometimes patients 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 (several brand names) or ampicillin (Omnipen, Polycillin) may stop bacterial overgrowth and allow vitamin B12 absorption to return to normal. Vitamin B12 deficiency resulting from inadequate dietary intake is the easiest to treat. Oral vitamin B12 supplements and adding foods containing B12 will reverse the condition.

When the anemia is severe and the red-blood-cell count is extremely low, blood transfusions may be necessary for the first couple of days until the vitamin B12 injections begin working.

When To Call A Professional

Contact your doctor for a physical examination if you experience unexplained fatigue, palpitations, shortness of breath, sore tongue or any other symptoms of vitamin B12 deficiency. This is especially true if you are a vegan, are older than age 50 and of African-American or Northern-European descent, have diabetes, have an autoimmune disorder or have had your stomach removed.


Prognosis is excellent because this form of anemia responds well to treatment. However, it is possible that nerve-cell damage will not improve. Some residual damage to the nervous system may remain in people who sought treatment late in the illness.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.