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L-carnitine: Supplements, What Works

L-carnitine is a substance that is essential for good health and for the regulation of fat oxidation in the body. Fatty acids are the main sources for energy production in the heart and the skeletal muscles, and these organs are especially vulnerable to L-carnitine deficiency. Symptoms of deficiency include muscle weakness, severe confusion, and angina.

Certain groups of people are at particular risk for L-carnitine deficiency, including kidney failure patients on hemodialysis, patients with liver failure, and patients receiving total parenteral (IV) nutrition. Some healthy individuals also have increased needs for dietary L-carnitine, including strict vegetarians, premature infants, pregnant women, and nursing mothers.

Dietary sources of L-carnitine are red meat, especially lamb and beef, and dairy products. There is little or no L-carnitine in vegetables, fruits, and cereals. How much L-carnitine is needed in the diet for optimal health is not known.

L-carnitine supplements are available in both the DL form and the L form. Only the L-carnitine form should be used, since the DL form has been shown to cause a muscle weakness syndrome in some individuals. Large doses of L-carnitine may cause diarrhea. Supplements may vary in purity.

Among the claims made for L-carnitine are that it increases blood flow and enhances energy production during exercise. Athletes and bodybuilders often use it.

  • Cardiovascular protection. A number of well-designed clinical studies have shown that L-carnitine supplementation does have protective effects with heart patients. According to Bartels, Singh, and others, it appears to reduce angina and ischemia, and can significantly improve exercise duration. In patients with suspected myocardial infarction, it reduces infarction size, angina, cardiac death, and nonfatal infarction.


  • Exercise performance. Evidence for improved exercise performance among athletes is not as convincing. In a 1997 review by Dr. Pamela Peeke, researchers found no controlled studies indicating improved physical performance in athletes. Two studies, one by Otto in 1987 and the other by Kasper in 1994, found that it did not produce an improvement for competitive runners.


  • Lipid metabolism. Clinical studies are inconclusive on whether carnitine supplementation enhances the oxidation of fatty acids. A 1993 study by Natali found that L-carnitine did not influence lipid metabolism at rest, but did during exercise. However, two other studies found no effect, as reported by Decombaz in 1993 and Oyono-Enguelle in 1988.

While L-carnitine supplementation may help with deficiency states, there is little evidence that it helps healthy people.



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Copyright © 2000 by Dr. Kenneth R. Pelletier, Inc.
Reprinted by permission of Simon & Schuster, Inc., New York, New York.

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