Muscular activity depends on your body's ability to convert fatty acids into energy. Carnitine is an amino acid that is essential for this conversion. A typical daily diet contains 5 to 100 mg of carnitine. The body produces carnitine in the liver and kidneys and stores it in the skeletal muscles and heart, as well as in sperm and in the brain.

Some people cannot properly use carnitine from their diet or suffer from dietary deficiencies of this nutrient. As a result, they may develop heart disease, skeletal muscle weakness, or low blood sugar. If you experience these symptoms and are found to have carnitine deficiency, your health care provider may recommend use of the supplement levocarnitine, or L-carnitine.

L-carnitine offers a variety of potential therapeutic uses, primarily related to the heart.

• Preventing heart disease
• Improving heart function in people with congestive heart failure
• Reducing heart damage when taken soon after a heart attack
• Reducing the pain of angina
• Treating cardiac arrhythmia (irregular heartbeat) without affecting blood pressure
• Reducing blood triglycerides and overall cholesterol levels while increasing HDL, or good cholesterol.

Your health care provider may also recommend taking L-carnitine if you have other health conditions, including the following:

• Alcoholism
• Alzheimer's disease
• Anorexia
• Chronic fatigue syndrome
• Diabetes
• Down's syndrome
• Epilepsy (childhood)
• Hemodialysis
• Immunosuppression
• Male infertility

Carnitine may also be recommended as a weight-loss aid.

Red meats are the primary dietary source of L-carnitine. Other animal-based foods containing L-carnitine include fish, poultry, and milk products. Tempeh (fermented soybeans), wheat, and avocados also contain this nutrient.

Carnitine is available as a supplement in several forms. Only the L-carnitine forms are recommended. These include the following:

• L-carnitine (LC), which is the most widely available, is the least expensive, and has been studied the most
• L-acetylcarnitine (LAC), which appears to be best for Alzheimer's disease and brain defects
• L-propionylcarnitine (LPC), which may be best for angina and other heart problems

The D-carnitine form should not be used because it has produced undesirable side effects.

Certain L-carnitine products have been approved by the U.S. Food and Drug Administration for medical use and are available only with your health care provider's prescription. Others are sold as supplements and should not be used to treat serious carnitine deficiency.

Recommended doses of L-carnitine vary depending on the health condition being treated. The following list provides guidelines for the most common uses:

• To improve fat metabolism and muscular performance: 1,000 mg to 2,000 mg usually divided into two doses
• For treatment of heart disease: 600 to 1,200 mg three times daily, or 750 mg twice daily
• For treatment of alcohol-related deficiencies: 300 mg three times daily
• For treatment of male infertility: 300 to 1,000 mg three times daily

L-carnitine is not recommended for people with active liver or kidney disease. If you take L-carnitine as a supplement to improve fat metabolism and muscular performance, it is recommended that you skip using it one week each month. If you take it in large quantities (5 g a day by an adult), you may experience diarrhea.

Additional research into the long-term safety of L-carnitine as a supplement is needed.

Blood levels of carnitine may be reduced by the anticonvulsant medication valproic acid and may cause carnitine deficiency. Taking carnitine supplements may prevent deficiency and may also reduce the side effects of valproic acid. Please refer to the depletions monograph for more information.

In a laboratory study, L-carnitine supplementation protected muscle tissue against toxic side effects from treatment with AZT, a medication used to treat AIDS. Additional studies are needed to confirm whether carnitine would also have this effect in people. Consult with your healthcare practitioner before taking carnitine supplements if you are currently taking AZT.

Treatment with carnitine also protected heart cells against the toxic side effects of doxorubicin, a chemotherapy medication, without reducing the effectiveness of the chemotherapy in studies in both animals and children. If you are currently being treated with doxorubicin, consult with your healthcare provider about whether carnitine may be appropriate for you before you start taking these supplements.

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