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Here's a dose of B12 facts

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Q: Are you sure you meant to recommend only 6 mcg of vitamin B12 in your recent column? My cardiologist put me on 2,000 mcg daily (1,000 mcg twice daily), along with the same levels of folate (400 mcg) and vitamin B6 (2 mg) you recommended.

A: The recommended dose of vitamin B12 varies according to your particular needs. The 6 mcg dose provides adequate levels for most people. Amounts such as this, designed to prevent a B12 deficiency, are present in general multivitamin supplements.

In contrast, your physician has prescribed a much higher, therapeutic dose of vitamin B12. This suggests that you might have a B12 malabsorption disorder or pernicious anemia.

Pernicious anemia is a vitamin B12 deficiency caused by lack of intrinsic factor, a stomach substance required for proper absorption of B12 by the body. In this case, B12 is typically given by injection to bypass the stomach; however, because a small percentage of B12 can be absorbed even in the absence of intrinsic factor, large doses taken by mouth can provide adequate amounts.

People with high homocysteine levels will benefit from B12 supplementation in combination with folate (folic acid) and vitamin B6. These vitamins have been found to hold down homocysteine levels. Excessive levels of the amino acid homocysteine can damage arteries and contribute to the plaque buildup associated with heart disease.

The homocysteine-lowering action of this vitamin combination also helps arteries stay open in people who have undergone coronary angioplasty.

Vegetarians and older people may benefit from B12 supplementation.

Vitamin B12 is found primarily in animal foods, and strict vegetarians don't eat these foods.

People over age 50 tend to have lower levels of stomach acid, and adequate stomach acid is required for proper absorption of B12 from foods.

People taking drugs for stomach ulcers, which reduce stomach acid, also may benefit from B12 supplementation. These include the H2 blockers cimetidine (Tagamet), famotidine (Pepcid), nizatidine (Axid) and ranitidine (Zantac), and the proton pump inhibitors esomeprazole (Nexium), lansoprazole (Prevacid), omeprazole (Prilosec, Losec), pantoprazole (Protonix, Pantoloc), and rabeprazole (Aciphex).

Individuals who take metformin (Glucophage, Glucovance, Avandamet, Metaglip) for type 2 diabetes should be aware that this drug might cause malabsorption of vitamin B12. Of special concern is the finding in one study that metformin-induced B12 malabsorption could persist after the drug is stopped. Interestingly, a different study found that calcium supplementation could partially reverse this effect (researchers think that metformin might interfere with calcium-dependent intestinal absorption of B12).

Based on these findings, calcium supplementation may be advisable during metformin therapy, as well as medical monitoring to prevent a B12 deficiency and to assess the need for B12 supplementation.

(Richard Harkness is a consultant pharmacist who writes on health care topics. You can write him at 1224 King Henry Drive, Ocean Springs, MS 39564. His e-mail address is Volume of mail prohibits individual replies; selected letters will be answered in his column.) Visit The Sun Herald Online at Distributed by Knight Ridder/Tribune Information Services.

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