L-Carnitine

Overview

L-carnitine is an amino acid that is synthesized from the amino acids lysine and methionine. Because it can be synthesized in the body, L-carnitine is usually not considered to be an essential nutrient. However, it could be classified as an essential nutrient for premature infants and other individuals who are not able to synthesize it in sufficient amounts. In addition to its use in clinical conditions, L-carnitine is used with exercise programs to reduce muscle soreness.

Dosage Info

Dosage Range

500 milligrams to 4 grams daily.

Most Common Dosage

250mg, 2 times a day.

Dosage Forms

Tablets, capsules, and powder.

Adult RDI

None established

Adult ODA

None established

Active Forms

L-carnitine, L-acetylcarnitine (LAC), and L-propionylcarnitine (LPC).

Absorption

There are two mechanisms for L-carnitine absorption in the duodenum: active transport process and passive diffusion.

Toxicities & Precautions

General

There is no known toxicity associated with L-carnitine. However, the use of D-carnitine should be avoided. It competes with L-carnitine and can cause a depletion of L-carnitine in the heart and skeletal muscles, which can result in muscle pain, decreased exercise tolerance, and loss of muscle function.

Functions in the Body

Energy Production:

One of L-carnitine’s primary functions is to transport long-chain fatty acids into the mitochondria where they undergo beta-oxidation in the production of energy.

Branched Chain Amino Acid Conversion:

L-carnitine also helps convert the branched chain amino acids to their keto-acid analogues. This enables the branched chain amino acids to be utilized for energy in conditions where there is a lack of carbohydrates such as fasting, starvation, or people who are on low carbohydrate diets.

Clinical Applications

Aids

High dose L-carnitine administration (6 gram/day for two weeks) to patients treated with zidovudine provided significant improvement in immune response and lipid metabolism in patients with AIDS, irrespective of initial serum L-carnitine levels. (1)

Cardiac Arrhythmias

Patients given 2 grams of L-carnitine 3 times daily for two weeks had a significant reduction in arrhythmic ventricular ectopic beats (VEB). (2)

Chemopreventative Effects

Cancer patients undergoing chemotherapy often experience fatigue. Ifosfamide and cisplatin cause a urinary loss of carnitine. One of the functions in the body of carnitine is energy production. Fifty patients who had low plasma carnitine levels, experienced fatigue during ifosfamide or cisplatin therapy and were not anemic were recruited for this observational study. The participants received 4 g of oral levocarnitine daily for 7 days. The mean Functional Assessment of Cancer Therapy Fatigue score improved from 19.7 at baseline to 34.9 following therapy. Also, all patients achieved normal plasma carnitine levels. These improved scores were maintained until the next cycle of chemotherapy. (3)

Alcoholic Liver Disease

The lipid-lowering effect of L-carnitine helps prevent alcohol-induced hyperlipemia and accumulation of fat in livers. (4) , (5)

Elevated Cholesterol

Treatment with 1 gram/day resulted in significant lowering of elevated serum cholesterol and approximately a 15 percent increase in HDL levels. (6)

Cardiomyopathy

A subpopulation of patients with cardiomyopathy respond well to L-carnitine treatment. (7)

Intermittent Claudication

L-propionylcarnitine was reported to be more effective than L-carnitine at improving walking capacity in patients with peripheral vascular disease. (8)

Kidney Dialysis

L-carnitine losses contribute to hyperlipidemia during long-term dialysis and L-carnitine supplementation is reported to help in the management of this condition in patients undergoing regular dialysis. (9) , (10) , (11)

Male Infertility

47 men with low sperm counts for longer than two years were given one gram of L-carnitine 3 times daily for three months. 79 percent responded favorably with approximately a doubling of both sperm counts and sperm motility. (12) In slightly larger studies, l-carnitine supplementation increased semen quality in men with lower baseline levels. (13) , (14)

Diabetes Mellitus

Both plasma and urine levels of L-carnitine are reported to be substantially reduced in diabetic patients (15) and treatment with L-carnitine significantly improved insulin sensitivity in insulin-resistant patients with Type 2 diabetes. (16)

Angina Pectoris

Studies report that both L-carnitine (17) and L-propionylcarnitine (18) prolong exercise time and increase exercise tolerance in patients with angina.

Hyperthyroidism

Studies have been published that indicate L -carnitine antagonizes thyroid hormone in some tissues. A study by Benvenga, et al evaluated the clinical impact of these findings on hyperthyroid patients. This double-blind, placebo-controlled trial evaluated 50 hyperthyroid women for six months. The women were randomized to one of 5 groups ranging from strictly placebo to either 2 or 4 grams of carnitine per day for a period alternating with placebo use for a period. The trial concluded that the use of L-carnitine is effective in preventing and reducing the nine hyperthyroid related symptoms evaluated and has a beneficial effect on bone mineralization based on biochemical parameters evaluated. (19)

Symptoms and Causes of Deficiency

L-carnitine deficiency can result in muscle weakness, fatty acid abnormalities, and problems with glucose control. A number of conditions can cause a L-carnitine deficiency including:
a) Inadequate levels of the precursor amino acids lysine and methionine. This can be due to inadequate dietary intake, intestinal malabsorption, kidney or liver dysfunction, which impair L-carnitine synthesis; or, a deficiency of nutritional cofactors necessary for L-carnitine synthesis such as niacin, pyridoxine, ascorbic acid and iron.
b) Genetic disorders, which inhibit the biosynthesis of L-carnitine.
c) Kidney dialysis patients and individuals with Duchenne-type muscular dystrophy have been found to be L-carnitine deficient.
d) Occasionally pregnant women become L-carnitine deficient due to the large L-carnitine requirements of the growing fetus.
e) Infants utilizing L-carnitine-deficient soy formulas have become L-carnitine deficient.
f) The drugs valproic acid and zidovudine can cause the depletion of L-carnitine.

Dietary Sources

L-carnitine is only found in animal food sources such as meat, poultry, and dairy products. Human breast milk is an important source of L-carnitine for infants.

References

  1. View Abstract: De Simone C, et al. High Dose L-carnitine Improves Immunologic and Metabolic Parameters in AIDS Patients. Immunopharmacol Immunotoxicol. Jan1993;15(1):1-12.
  2. View Abstract: Mondillo S, et al. Therapy of Arrhythmia Induced by Myocardial iIschemia. Association of L-carnitine, Propafenone and Mexiletine. Clin Ter. Dec1995;146(12):769-74.
  3. View Abstract: Graziano F, Bisonni R, Catalano V, Silva R, Rovidati S, Mencarini E, et al. Potential role of levocarnitine supplementation for the treatment of chemotherapy-induced fatigue in non-anaemic cancer patients. British Journal of Cancer. Jun2002;86:1854-57.
  4. View Abstract: Sachan DS, et al. Ameliorating Effects of Carnitine and Its Precursors on Alcohol-induced Fatty Liver. Am J Clin Nutr. May1984;39(5):738-44.
  5. View Abstract: Lapinski TW, Grzeszczuk A. The impact of carnitine on serum ammonia concentration and lipid metabolism in patients with alcoholic liver cirrhosis. Pol Merkuriusz Lek. Jul2003;15(85):38-41.
  6. Pola P, et al. Statistical Evaluation of Long-term L-carnitine Therapy in Hyperlipoproteinemias. Drugs Exptl Clin Res. 1983;9:925-34.
  7. View Abstract: Winter S, et al. The Role of L-carnitine in Pediatric Cardiomyopathy. J Child Neurol. Nov1995;10(Suppl2):S45-51.
  8. View Abstract: Brevetti G, et al. Superiority of L-propionylcarnitine vs L-carnitine in Improving Walking Capacity in Patients with Peripheral Vascular Disease: An Acute, Intravenous, Double-blind, Cross-over Study. Eur Heart J. Feb1992;13(2):251-55.
  9. View Abstract: Elisaf M, et al. Effect of L-carnitine Supplementation on Lipid Parameters in Hemodialysis Patients. Am J Nephrol. 1998;18(5):416-21.
  10. View Abstract: Bellinghieri G. Carnitine and hemodialysis. Am J Kidney Dis. Mar2003;41(3 Suppl 1):S116-22.
  11. View Abstract: Vazelov E. L-carnitine consecutively administered to patients on hemodialysis improves beta-cell response. Int J Artif Organs. Apr2003;26(4):304-7.
  12. View Abstract: Vitali G, et al. Carnitine Supplementation in Human Idiopathic Asthenospermia: Clinical Results. Drugs Exp Clin Res. 1995;21(4):157-59.
  13. View Abstract: Lenzi A. Use of carnitine therapy in selected cases of male factor infertility: a double-blind crossover trial. Fertil Steril. Feb2003;79(2):292-300.
  14. View Abstract: Lenzi A, Sgro P, Salacone P, et al. A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and l-acetyl-carnitine treatment in men with asthenozoospermia. Fertil Steril. Jun2004;81(6):1578-84.
  15. View Abstract: De Palo E, et al. Plasma and Urine Free L-carnitine in Human Diabetes Mellitus. Acta Diabetol Lat. 1981;18(1):91-95.
  16. View Abstract: Mingrone G, et al. L-carnitine Improves Glucose Disposal in Type 2 Diabetic Patients. J Am Coll Nutr. Feb1999;18(1):77-82.
  17. View Abstract: Cherchi A, et al. Effects of L-carnitine on Exercise Tolerance in Chronic Stable Angina: A Multicenter, Double-blind, Randomized, Placebo Controlled Crossover Study. Int J Clin Pharmacol Ther Toxicol. Oct1985;23(10):569-72.
  18. View Abstract: Lagioia R, et al. Propionyl-L-carnitine: A New Compound in the Metabolic Approach to the Treatment of Effort Angina. Int J Cardiol. Feb1992;34(2):167-72.
  19. View Abstract: Benvenga S, Ruggeri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind, placebo-controlled clinical trial. J Clin Endocrinol Metab. Aug2001;86(8):3579-94.