L-carnitine is commonly taken as a sports and weight loss supplement and is classified as an ergogenic acid. It’s most important metabolic role is the transport of long chain fatty acids into the mitochondria of muscle cells. These fatty acids are then burnt for energy production. Anybody undergoing intense physical exercise should seriously consider carnitine supplementation !
Properties & Uses
- Essential for energy generation and fat metabolism.
- Required for transporting long chain fatty acids across cell membranes to the mitochondria so they can be oxidized for energy generation. The process is commonly termed beta-oxidation of fatty acids.
- Production of heat or thermogenesis in brown adipose tissue.
- Regulation of glucose production in a metabolic pathway called gluconeogenesis.
- A quaternary ammonium compound synthesised from two amino acids, methionine and lysine.
- Naturally synthesised in the liver and kidneys.
- Helps with fat regulation
- It is also thought to protect cells by acting as a free radical scavenger because it can bind iron which helps generate hydroxyl radicals.
- Infants and children may not produce enough and there are situations in adults where certain disease states lead to a deficiency.
- A common supplement is acetyl-L-carnitine which is a derivative of carnitine.
It was discovered at the turn of the 20th Century (Gulewitsch & Grimberg, 1905).
Carnitine has been called vitamin BT although that name appears to have fallen out of favour.
Its chemical name is L-3-hydroxy-4-N-N-N-trimethylaminobutyrate.
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The body holds about 20 to 25g of L-carnitine of which 95% is contained in skeletal muscle whilst the remainder is found in most other organs and plasma. Sports enthusiasts supplement with it to increase aerobic status, to spare the use of glycogen during continuous exercise, and improve performance of submaximal exercise and resistance to fatigue. One testament to its current popularity is one study showing that just over 60% of bodybuilders supplement with it and to high levels (Karimian and Esfahani, 2011).
In certain cases when exercising is vigorous, not enough carnitine is available and so energy metabolism based on fat oxidation is impeded. It is often deficient in babies, infants and adolescents which is a testament to its requirement in growth and development. It is also viewed as a weight loss supplement because of its role in fat burning, producing energy and improving resistance of muscle to tiredness and fatigue.
L-carnitine is naturally found in fish and meat especially beef and lamb, milk and dairy products.
What is the daily intake ?
It is estimated that at least 1 g per day of L-carnitine is needed for weight loss although levels up to 5 g daily have been suggested for obese individuals. For keen sports people and athletes, a dose of between 2g and 4g daily is suggested to encourage maximum fat burning but there are provisos.
Acetyl-L-Carnitine –What is it and how does it work in the body ?
L-carnitine is acetylated to acetyl-L-carnitine and has been implicated in benefiting those suffering end stage renal disease and heart disease. It is used in conjunction with lipoic acid to help reverse mitochondrial damage associated with ageing too.
Other evidence exists for its benefits in protecting those who have suffered from nerve damage and cerebral ischemia. Animal studies indicate it may also help those suffering from Parkinson’s disease (Zaitone et al., 2012).
Weight Loss Supplementation – Doubts ?
Some studies throw doubt on its activity as a weight loss supplement. The evidence is patchy and in some cases contradictory. In the 90s, both Barnett et al. (1994) and Vukovich et al., (1994) showed that short-term supplementation of L-carnitine, of 4 to 6 g/day for 7 to 14 days had no impact on muscle levels or on the benefit to metabolism. A double-blind evaluated 13 moderately overweight premenopausal women on 2g of L-carnitine twice daily for 8 weeks (Villani et al., 2000). It showed no significant change in the mean total body mass (TBM), the fat mass (FM) or resting lipid use which cast doubt on the claims.
Perhaps even more discouraging was the study in nature medicine that carnitine could increase the risk of heart disease although this was linked to eating too much red meat. Such a finding needs much more research. The suggested amounts of between 2g and 4g for sports people seems excessive and this level of supplementation needs caution.
A noted supplier Lonza which sponsored some research has reported findings that given the right level of motivation and a daily dose of 500mg of L-carnitine, overweight people can lose weight readily (Odo et al., 2013). This particular study was relatively small, double-blind and randomised with placebo-control. Twenty-four overweight Japanese men with a body mass index of between 25.8 to 26.6 kg/m2 were split into 4 groups. One group was given just 500mg L-carnitine whilst another received this amount along with the motivational training. The third group had a placebo and the final group also received this along with the motivational training. The study lasted just 4 weeks but the results showed statistical significance.
The researchers concluded that there were benefits in minimising the impact of metabolic syndrome. They looked at various risk parameters such as total triglyceride and adiponectin levels whose levels were significantly reduced. The group receiving the supplement along with the training showed the most weight loss which was on average 1.1kg compared to an increase of 0.7kg in the group receiving the placebo and no training.
There are a number of reviews and papers on the subject on the internet and all are worth consulting. The National Institutes of Health provides excellent advice on carnitine for all phases of life and levels of supplementation (NIH, 2013).
Heart Health And L-Carnitine
Patients who have recently suffered a heart attack or myocardial infarction appear to benefit from supplementing with carnitine and coenzyme Q10 (Sharifi et al., 2017). The same benefits extend to those patients undergoing haemodialysis.
In this study, 128 patients who had been hospitalised following heart attack were randomly split into four groups where they either had a therapeutic dietary change on its own, 150 mg per day of coenzyme Q10 plus 1200 mg per day L-carnitine, both diet and supplement together or just routine care. All patients receiving such treatments reported improvements in their physical and emotional health. Coenzyme Q10 and L-carnitine together appear to improve muscle and red blood cell metabolism. The addition of Q10 probably minimised the impact of statin myalgia which in turn improves their quality of life (QoL).
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Barnett, C., Costill, D.L., Vukovich, M.D., Cole, K.J., Goodpaster, B.H., Trappe, S.W. and Fink, W.J. (1994) Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high intensity sprint cycling. Int. J. Sport Nutr. 4 pp. 280–288
Gulewitsch, V.S. and Krimberg, G.R. (1905) Information about Muscle Extracts. Hoppe-Seyler’s Journal of Physiological Chemistry, Vol. 45, No. 3-4, pp. 326-330.
NIH (2013) Carnitine. Fact Sheet for Health Professionals. (Article)
Sharifi, M.H., Eftekhari, M.H., Ostovan, M.A., Rezaianazadeh, A. (2017) Effects of a therapeutic lifestyle change diet and supplementation with Q10 plus L-carnitine on quality of life in patients with myocardial infarction: A randomized clinical trial. J. Cardiovasc. Thorac. Res. 9(1) pp. 21-28. doi: 10.15171/jcvtr.2017.03.
Villani, R.G., Gannon, J., Self, M., Rich, P.A. (2000) L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women. Int. J. Sport Nutr. Exerc. Metab. 10(2) pp.199-207
Vukovich, M.D., Costill, D.L. and Fink, W.J. (1994). Carnitine supplementation: effect on muscle carnitine and glycogen content during exercise. Med. Sci.Sports Exercise 26 pp. 1122–1129