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Causes of vitamin B12 deficiency

Anthony L. Komaroff M.D.

DEAR READERS: In yesterday’s column I began to answer a reader’s question about the different causes of vitamin B12 deficiency. Today, we continue a discussion of the many conditions that can interfere with the ability of the small intestine (the part called the ileum) to absorb vitamin B12 from the foods you eat.

I’m one of those folks who don’t absorb much of the vitamin B12 in food. Even though I eat plenty of B12-rich foods, I also need to take B12 pills. That fixes the problem. Most people with this condition are like me: Vitamin B12 pills are enough, and we don’t need shots. And, sometimes, just increasing the B12-rich foods in your diet is enough – you don’t even need pills.

B12 is found naturally only in animal products. Examples include meat, fish, poultry, eggs and milk. Many cereals are fortified with the synthetic form of the vitamin.

If you are deficient because you are not getting enough B12 in your diet, or because of aging, pills may not always be enough. If your blood levels of B12 are very low, your doctor may prescribe vitamin B12 shots for a while. It’s easier to “fill your tank” with shots. Then, once your blood levels are normal, you can switch to pills.

There are other ailments in which not enough of the vitamin B12 in the diet is absorbed by the gut. There are rare conditions (besides pernicious anemia) that are inherited. Conditions that reduce the amount of acid produced in the stomach can do it. Examples are chronic gastritis, or surgical removal of part of the stomach to treat an ulcer.

Long-term use of powerful acid-suppressing pills – such as omeprazole (Prilosec) or cimetidine (Tagamet) – can cause B12 deficiency. So can the commonly prescribed medicine for diabetes, metformin (Glucophage). When metformin is the culprit, adding a calcium supplement can fix the problem.

Other diseases of the ileum besides Crohn’s disease (which we discussed in yesterday’s column) can cause low B12 levels. Examples are infections of the ileum, such as by tuberculosis or possibly by HIV, or cancer of the ileum (lymphoma).

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