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L-carnitine is made in the body from the amino acids lysine and methionine, and is needed to release energy from fat. It transports fatty acids into mitochondria, the powerhouses of cells. In infancy, and in situations of high energy needs, such as pregnancy and breast-feeding, the need for L-carnitine can exceed production by the body. Therefore, L-carnitine is considered a "conditionally essential" nutrient.1
Dairy and red meat contain the greatest amounts of carnitine. Therefore, people who have a limited intake of meat and dairy products tend to have lower L-carnitine intakes.
This is a good supplement to take if you exercise, particularly if you participate in endurance activities, such as running. It helps with transporting fatty acids into the mitochondria, so L-carnitine may make exercise more productive, particularly among obese people.
L-carnitine, which is normally manufactured by the human body, has been popular as a potential ergogenic aid (i.e., having the ability to increase work capacity), because of its role in the conversion of fat to energy.2 However, while some studies have found that L-carnitine improves certain measures of muscle physiology, research on the effects of 2 to 4 grams of carnitine per day on performance have produced inconsistent results.3 L-carnitine may be effective in certain intense exercise activities leading to exhaustion,4 but recent studies have reported that L-carnitine supplementation does not benefit non-exhaustive or even marathon-level endurance exercise,5 6 anaerobic performance,7 or lean body mass in weight lifters.8
L-carnitine has not been consistently linked with any toxicity.
The body needs lysine, methionine, vitamin C, iron, niacin, and vitamin B6 to produce carnitine.
Are there any drug interactions?
Certain medicines may interact with L-carnitine. Refer to drug interactions for a list of those medicines.
*Athletes and fitness advocates may claim benefits for L-carnitine based on their personal or professional experience. These are individual opinions and testimonials that may or may not be supported by controlled clinical studies or published scientific articles on L-carnitine. For more complete and detailed information, including references and safety information, see L-Carnitine as a nutritional supplement.
1. Giovannini M, Agostoni C, Salari PC. Is carnitine essential in children? J Int Med Res 1991;19:88-102.
2. Cerretelli P, Marconi C. L-carnitine supplementation in humans. The effects on physical performance. Int J Sports Med 1990;11:1–14 [review].
3. Heinonen OJ. Carnitine and physical exercise. Sports Med 1996;22:109–32 [review].
4. Bucci LR. Nutrients as ergogenic aids for sports and exercise. Boca Raton, FL: CRC Press, 1993, 47–52 [review].
5. Colombani P, Wenk C, Kunz I, et al. Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double blind crossover field study. Eur J Appl Physiol 1996;73:434–9.
6. Decombaz J, Deriaz O, Acheson K, et al. Effect of L-carnitine on submaximal exercise metabolism after depletion of muscle glycogen. Med Sci Sports Exerc 1993;25:733–40.
7. Trappe SW, Costill DL, Goodpaster B, et al. The effects of L-carnitine supplementation on performance during interval swimming. Int J Sports Med 1994;15:181–5.
8. Green RE, Levine AM, Gunning MJ. The effect of L-carnitine supplementation on lean body mass in male amateur body builders. J Am Dietet Assoc 1997;(suppl):A-72 [abstract].
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The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires February 2010.
