By Richard Harkness
Enquirer contributor

Question: My doctor said vitamin B12 and L-carnitine are not absorbed by the gastrointestinal tract. If so, why are they being sold and why are people taking them? Are there any real benefits for L-carnitine?

Answer: Like most anything normally taken by mouth, these two supplements are absorbed into the bloodstream as they travel through the small intestines. The extent and rate of absorption may vary depending on a number of factors.

Drugs taken for stomach ulcers, which work by reducing stomach acid, can decrease the absorption of B12 from food, but they should not interfere with the absorption of B12 from supplements.

Adequate stomach acid and pepsin (an enzyme normally present in the stomach) are required to free B12 from its dietary protein-bound form. Since supplemental B12 is not protein-bound, it does not need stomach acid and pepsin for its absorption.

The most common cause of vitamin B12 deficiency is lack of intrinsic factor (a substance normally present in the stomach), a serious condition called pernicious anemia. In this case, B12 is typically given by injection to bypass the stomach.

As for carnitine, it is an amino acid the body uses to help convert fat into energy.

Carnitine is taken in three forms: L-carnitine (for heart and other conditions), propionyl-L-carnitine (for heart conditions), and acetyl-L-carnitine (for Alzheimer's disease). The adult daily dose usually ranges from 1,500 to 6,000 mg, given in three divided doses.

Carnitine supplements are used primarily for heart-related conditions in combination with conventional medications. Heart muscle tissue, because of its high energy requirements, is particularly vulnerable to carnitine deficiency.

Carnitine may improve symptoms and reduce medication needs in the treatment of angina. When added to conventional treatment, it may reduce the risk of death after a heart attack.

Carnitine may be beneficial in treating intermittent claudication (pain in the legs after walking due to plaque-narrowed arteries), congestive heart failure and cardiomyopathy. This supplement also may improve exercise ability in individuals with the lung disease emphysema.

Some evidence suggests that acetyl-L-carnitine might be helpful in Alzheimer's disease, depression in the elderly and HIV infection.

A caution: Do not attempt to self-treat serious medical conditions or use carnitine as a substitute for standard drug treatment.

E-mail rharkn@aol.com.