Although there is generally a plentiful supply of L-carnitine available in a healthy diet, supplementation can ensure that a deficiency does not occur. Supplements are available in the form of L-carnitine or its acetylated derivative, acetyl L-carnitine.

Since the fatty acid triglycerides contained in body fats are a major source of energy in the heart and skeletal muscles, it is easy to understand how L-carnitine is believed to lead to the increased energy levels required for stamina and staying power. A major reason for its effect on longer-term or extended energy requirements is that in enabling stored body fats to be used for immediate and longer-term energy requirements, L-carnitine allows emergency glycogen (condensed sugar molecules that store in muscle) stores to be retained for use once immediate fatty acid supplies or those of carnitine have been depleted, and so allows the energy supply to be extended even farther.

Research has also suggested that the amino acid can possibly be used to treat liver and kidney disease, diabetes and chronic fatigue syndrome.

As with many supplements, the question is often asked how does L-carnitine work in practice as opposed to the claims made for it by the supplement providers? Recent research indicates mixed results, but sufficient to justify its use. It is generally accepted that a supplement is necessary when there is a deficiency, but once that deficiency has been corrected further intake is unnecessary. However, it is also believed that during long and extended periods of exercise a carnitine deficiency does occur as L-carnitine is used up, and the supplement is necessary to ensure sufficient energy supply throughout the period of exercise.

There has also been a case reported in the Journal of Clinical Neurology (Negoro, Tsuda, Kato & Morimatsu, 1995) where a deficiency, caused by anorexia nervosa damaging the liver to the extent that it was unable to synthesize L-carnitine, was remedied by means of an oral supplement. Studies on endurance athletes have been mixed, ranging from no effect to L-carnitine being found to promote weight loss.

Carnitine has no unknown harmful side effects, and has been studied for medical applications other than as an energy supplement. For example it possesses extensive antioxidant properties, and can be used as a supplement against oxidative stress and the prevention of the lipid peroxidation that is a precursor to atherosclerosis (narrowing of the arteries).

Its use in osteoporosis and reducing bone mass is also being studied. The concentration of L-carnitine diminishes with age, and affects fatty acid metabolism in a number of tissues. Bones are particularly affected since they require continuous reconstruction. Without detailing the biochemistry involved in this, administration of carnitine helps to reduce the speed by which this occurs. Trials are so far been carried out only on animals.

In studies on both healthy volunteers and patients with type II diabetes, L-carnitine was found to improve storage of glucose in both groups, although its oxidation increased only in the group with diabetes.

Other studies carried out include improving the function of neurotransmitters in the brains of elderly patients and in the treatment of Alzheimer's and Parkinson's disease, and other neurological disorders.

In conclusion then, although the jury is out on the use of L-carnitine as an energy-giving or weight-loss supplement, it appears to be effective where the body's stores of carnitine could be depleted such as with long-term exercise, natural deficiencies or deficiencies caused through age. It is also under study in the treatment of various medical conditions. On balance, it would appear that the prospective benefits of L-carnitine render it worthy of use.