Acetyl-L-Carnitine may be beneficial in preventing age-related declines; better bioavailability

Acetyl-L-Carnitine (or ALCAR) is a naturally occurring molecule synthesised from L-Carnitine inside mitochondria by carnitine O-acetyltransferase enzyme [1]. Acetyl-L-carnitine is a form of carnitine with acetyl group attached and is available as a supplement. In the terms of bioavailability acetyl-l-carnitine is claimed to be superior to L-Carnitine [2]. Both are sold as a dietary supplement and are often promoted as an aid for weight loss, to improve exercise performance, and to enhance a sense of well-being [3].

Bioavailability – Acetyl-l-carnitine vs L-carnitine

Researchers prefer to use acetyl-L-carnitine in research studies because of its better absorption from the small intestine than L-carnitine. It also more efficiently crosses the blood-brain barrier (i.e., gets into brain tissue) [4]. According to Charles J. Rebouche, bioavailability of oral l-carnitine supplementation (0.5-6 grams) ranges from 14%-18% of the total dose [5]. Bioavailability of the acetylated form of L-carnitine (Acetyl-L-Carnitine) is thought to be higher than L-carnitine, however, not much is known regarding its metabolism. In humans, circulating acetyl-l-carnitine concentration was increased by 43% after oral acetyl-l-carnitine supplements of 2 g/day [5].

Aging and disease prevention

Carnitine is thought to contribute to the aging process because its concentration in tissues declines with age and thereby reduces the integrity of the mitochondrial membrane [6]. Acetyl-L-carnitine supplementation may be beneficial in preventing age-related declines in energy metabolism, decreased oxidative stress, and improved memory, studies conducted on rats report [7,8]. ALCAR supplementation in rats has also been shown to reversed the age-related declines in tissue L-carnitine levels [9].

Acetyl-L-Carnitine has been shown to increase cognition in patients suffering from dementia of Alzheimer’s disease [4].

How much L-carnitine should you take?

After reviewing the studies on the function of carnitine Food and Nutrition Board (FNB) of the National Academy of Sciences concluded that carnitine is not an essential nutrient [10]. Therefore, healthy children and adults do not need to supplement with it, as liver and kidney produce sufficient amounts (from the amino acids lysine and methionine)[11]. The FNB has not established recommended dietary allowance (RDA)—for carnitine [12].

[the_ad id=”28979″]

References

1. Zeyner, Annette, and J. Harmeyer. “Metabolic functions of L‐Carnitine and its effects as feed additive in horses. A review.” Archives of Animal Nutrition 52.2 (1999): 115-138.
2. Hosein, E. A., and Jennie M. Smoly. “Biosynthesis of acetyl-l-carnityl choline.” Archives of Biochemistry and Biophysics 114.1 (1966): 102-107.
3. Carnitine: lessons from one hundred years of research. Ann NY Acad Sci. 2004;1033:ix-xi.
4. Dietary Supplement Fact Sheet: Carnitine – Office of Dietary Supplements Retrieved 13. April 2013
5. Rebouche, Charles J. “Kinetics, Pharmacokinetics, and Regulation of l‐Carnitine and Acetyl‐l‐carnitine Metabolism.” Annals of the New York Academy of Sciences 1033.1 (2004): 30-41.
6. Ames, Bruce N., and Jiankang Liu. “Delaying the mitochondrial decay of aging with acetylcarnitine.” Annals of the New York Academy of Sciences 1033.1 (2004): 108-116.
7. Liu, Jiankang, 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-α-lipoic acid.” Proceedings of the National Academy of Sciences 99.4 (2002): 2356-2361.
8. Hagen, Tory M., et al. “Feeding acetyl-L-carnitine and lipoic acid to old rats significantly improves metabolic function while decreasing oxidative stress.” Proceedings of the National Academy of Sciences 99.4 (2002): 1870-1875.
9. Hagen, Tory M., et al. “Acetyl-L-carnitine fed to old rats partially restores mitochondrial function and ambulatory activity.” Proceedings of the National Academy of Sciences 95.16 (1998): 9562-9566.
10. Shils, Maurice Edward. Modern nutrition in health and disease. Lippincott Williams & Wilkins, 2006.
11. National Research Council. Food and Nutrition Board. Recommended Dietary Allowances, 10th Edition. National Academy Press, Washington, DC, 1989.
12. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes. 2005. http://www.iom.edu/project.asp?id=4574.