Acetyl-L-Carnitine:
Does it offer any benefit as a supplement?
What is Acetyl-L-Carnitine?
Acetyl-L-carnitine (ALC) is a compound derived from the amino acid, L-carnitine, and is produced in the human brain, liver, and kidneys by an enzyme called acetyl-L-carnitine-transferase. ALC facilitates the movement of a coenzyme into the mitochondria during fatty acid oxidation, a process essential for energy synthesis. It enhances the production of acetylcholine, a chemical that transmits signals across nerve cells, and it stimulates the production of the major structural components of cell membranes. Studies have shown that ALC may be of benefit in treating Alzheimer's dementia, depression in the elderly, HIV infection, diabetic neuropathies, ischemia and reperfusion of the brain, and cognitive impairment of alcoholism 1-3.
What is L-Carnitine?
Acetyl-L-carnitine is often confused with L-carnitine; however, they are very different in structure and perform different functions in our body. L-carnitine is produced with the merging of two amino acids: lysine and methionine and is stored primarily in the skeletal muscles and the heart, where it is used to transform fatty acids into energy. It can also be produced in the liver if there are sufficient amounts of lysine, thiamin (vitamin B1), vitamin B6, and iron. It plays a major role in the metabolism of fat and the reduction of triglycerides by increasing the utilization of fat in the liver. Deficiencies can increase symptoms of fatigue, angina (chest pain), muscle weakness, and confusion.
Although many manufacturers tout claims that L-carnitine can improve athletic performance and endurance, as well as facilitate weight loss, there are no studies to substantiate that. L-carnitine is sometimes prescribed under a physician's care for deficiencies due to genetic defects; malabsorption, or increased loss resulting from hemodialysis; Fanconi syndrome; and the metabolism of some medications. It is also interesting to note that L-carnitine levels have been found to decline with age in humans and animals 4. Although studies in rats have shown that high doses of L-carnitine and alpha-lipoic acid improve memory and energy synthesis, it is not yet known whether taking relatively high doses of these two naturally occurring substances will benefit rats in the long-term or will have similar effects in humans5-6. Clinical trials in humans are planned, but it will be several years before the results are available.
What are the Potential Applications for Acetyl-L-Carnitine?
Alzheimer’s Disease:
Several studies have demonstrated the effectiveness of ALC in improving cognitive performance in patients suffering from Alzheimer's dementia. These studies were usually three to six months in length and oral dosages ranged from one to three grams per day. Although results varied, improvements were generally noted in spatial learning tasks, timed tasks of attention, discrimination-learning tasks, and tasks of personal recognition 7-9. At a dosage of two grams daily, one study demonstrated a decrease in deterioration of reaction time, in addition to improvement in short-term memory-related tasks 7. Studies on the long-term effects of ALC administration are few, but one of them demonstrated that one to two grams daily for one year resulted in a decrease in behavioral deterioration, and an improvement in long-term memory performance 10.
Depression:
Studies have demonstrated that cortisol secretion appears to be much higher in depressed patients 11. Animal studies have indicated ALC administration may have an inhibitory effect on the system that is responsible for the cortisol secretion, thus reducing the levels of cortisol, resulting in an improvement in depressive symptoms. However, this has not been observed in human studies 12. In a two-month study of 24 depressed elderly patients, it was demonstrated that ALC treatment was highly effective, particularly in patients with more serious depressive symptoms 13. In another study of 28 elderly patients, 500 mg of ALC three times per day was effective in counteracting symptoms of depression 14. Patients in both studies had decreased scores when evaluated using the Hamilton Rating Scale for Depression, showing an improvement in depressive symptoms.
Diabetic Neuropathy:
Approximately one-third of diabetic patients are affected by peripheral neuropathy. Animal studies have shown a link between imbalances in carnitine metabolism and abnormalities associated with diabetic polyneuropathy 15. Currently no human studies are available on the use of ALC in tablet form and its affects on diabetic neuropathy. The human studies that have been done used an injectable form of the supplement. These studies did show a decrease in neuropathy-associated pain and improved nerve function 16-17.
Summary: There does appear to be some effectiveness with the use of supplemental acetyl-L-carnitine; however, it is important to note that most studies have been conducted on animals. We cannot merely translate the findings and assume that the same benefits would be demonstrated in humans. The best advice is to talk with your personal physician if you are considering using ALC as a supplement. In the meantime, you should continue to read and learn about its use as more studies are conducted on humans.
References:
- Murray M, Pizzorno J. Encyclopedia of Natural Medicine. Rocklin, CA: Prima Publishing;1998:230.
- Spagnoli A, Lucca U, Menasce G, et al. Long-term acetyl-L-carnitine treatment in Alzheimer's disease. Neurology 1991;41:1726-1732.
- Furlong JH. Acetyl-L-Carnitine: Metabolism and applications in clinical practice. Altern Med Rev 1996;1:85-93.
- Costell M, O'Connor JE, Grisolia S. Age-dependent decrease of carnitine content in muscle of mice and humans. Biochem Biophys Res Commun. 1989;161(3):1135-1143.
- Hagen TM, Liu J, Lykkesfeldt J, et al. Feeding acetyl-L-carnitine and lipoic acid to old rats significantly improves metabolic function while decreasing oxidative stress. Proc Natl Acad Sci U S A. 2002;99(4):1870-1875.
- Liu J, Head E, Gharib AM, et al. Memory loss in old rats is associated with brain mitochondrial decay and RNA/DNA oxidation: partial reversal by feeding acetyl-L-carnitine and/or R-alpha -lipoic acid. Proc Natl Acad Sci U S A. 2002;99(4):2356-2361.
- Rai G, Wright G, Scott L, et al. Double-blind, placebo controlled study of acetyl-l-carnitine in patients with Alzheimer's dementia. Curr Med Res Opin 1990;11:638-647.
- Bonavita E. Study of the efficacy and tolerability of L-acetylcarnitine therapy in the senile brain. Int J Clin Pharm Ther Toxicol 1986;24:511-516.
- Sano M, Bell K, Cote L, et al. Double-blind parallel design pilot study of acetyl levocarnitine in patients with Alzheimer's disease. Arch Neurol 1992;49:1137-1141.
- Spagnoli A, Lucca U, Menasce G, et al. Long-term acetyl-L-carnitine treatment in Alzheimer's disease. Neurology 1991;41:1726-1732.
- Gecele M, Francesetti G, Meluzzi A. Acetyl-L-carnitine in aged subjects with major depression: clinical efficacy and effects on the circadian rhythm of cortisol. Dementia 1991;2:333-337.
- Angelucci L, Ramacci MT. Hypothalamo-pituitary-adrenocortical functioning in aging: Effects of acetyl-l-carnitine. In: DeSimone C, Martelli EA, eds. Stress, Immunity and Aging, A Role for Acetyl-L-Carnitine. Amsterdam: Elsevier; 1989.
- Tempesta E, Casella L, Pirrongelli C, et al. L-acetylcarnitine in depressed elderly subjects. A cross-over study vs placebo. Drugs Exp Clin Res 1987;13:417-423.
- Garzya G, Corallo D, Fiore A, et al. Evaluation of the effects of L-acetylcarnitine on senile patients suffering from depression. Drugs Exp Clin Res 1990;16:101-106.
- Ido Y, McHowat J, Chang KC, et al. Neural dysfunction and metabolic imbalances in diabetic rats. Prevention by acetyl-L-carnitine. Diabetes 1994;43:1469-1477.
- Onofrj M, Fulgente T, Melchionda D, et al. L-acetylcarnitine as a new therapeutic approach for peripheral neuropathies with pain. Int J Clin Pharm Res 1995;15:9-15.
- Lowitt S, Malone JI, Salem AF, et al. Acetyl-L-carnitine corrects the altered peripheral nerve function of experimental diabetes. Metabolism 1995;44:677-680.
Angela Marks is the Director of Operations for Cooper Concepts, Inc., a division of The Cooper Aerobics Center. Cooper Concepts, Inc. develops and markets health-related products including the Cooper CompleteŽ vitamins and supplements. The division is also responsible for the weekly radio show "Healthy Living Radio with Dr. Ken Cooper." Prior to her current position, she was the Project Director for the initial research study on the Cooper CompleteŽ multivitamin. She co-authored "Effect of Cooper Complete on Glucose Levels" published in Diabetes, 60th Scientific Sessions.
Marks has a bachelors of science degree in education with an emphasis on health promotion and an MBA from Baylor University. She is also certified by the Cooper Institute as a health promotion director, a physical fitness specialist and in the biomechanics of strength training. Well versed on a variety of health and wellness topics, Marks' expertise lies in the discussion of supplementations and vitamins.