Carnitine

L-carnitine is a conditionally essential micronutrient synthesized from the essential amino acids L-lysine and L-methionine primarily in the human brain, liver, and kidney. Once synthesized, carnitine is transported to other parts of the body, especially cardiac and skeletal muscle where 98% of total body carnitine is confined.

Carnitine plays an important role in fat and carbohydrate metabolism and energy production by transporting long-chain fatty acids into the mitochondria where beta-oxidation of the fatty acids produces energy in the form of ATP (adenosine-5’-triphosphate). Carnitine facilitates oxidation of glucose, branched-chain amino acids, and ketones, and is required for the oxidation of medium-chain fatty acids in cardiac and skeletal muscle, tissues that use fatty acids as their primary fuel [1,2].

Muscle fuel metabolism also depends on carnitine when fatty acids become the primary energy source for muscles during ongoing low to moderate exercise. Increasing total muscle carnitine content in healthy humans may support physiological function by reducing muscle glycolysis and increasing glycogen storage, fat oxidation, and work output [3,4]. A randomized, placebo-controlled human subject study suggested that carnitine can improve exercise tolerance and inspiratory muscle strength, as well as reduce lactate production [5]. A six-month, randomized, double-blind, placebo-controlled study of 50 children suggested that oral supplementation with L-carnitine helped support normal carnitine levels in the body with statistically significant positive effects on support of lung function [6].

References

1. Natural Standard Database. www.NaturalStandard.com. Accessed February 24, 2012.
2. Linus Pauling Institute. http://lpi.oregonstate.edu/mic/dietary-factors/L-carnitine. Accessed August 23, 2016.
3. Stephens FB, Constantin-Teodosiu D, Greenhaff PL. New insights concerning the role of carnitine in the regulation of fuel metabolism in skeletal muscle. J Physiol. 2007 Jun 1;581(Pt 2):431-44. Review. [PMID: 17331998]
4. Wall BT, Stephens FB, Constantin-Teodosiu D, et al. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. J Physiol. 2011 Feb 15;589(Pt 4):963-73. [PMID: 21224234]
5. Borghi-Silva A, Baldissera V, Sampaio LM, et al. L-carnitine as an ergogenic aid for patients with chronic obstructive pulmonary disease submitted to wholebody and respiratory muscle training programs. Braz J Med Biol Res. 2006 Apr;39(4):465-74. [PMID: 16612469]
6. Al-Biltagi M, Isa M, Bediwy AS, et al. L-carnitine improves the asthma control in children with moderate persistent asthma. J Allergy (Cairo). 2012;2012:509730. [PMID: 22162707]