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L-carnitine is a compound derived from lysine, one of the eight essential amino acids required by the body. Although it is often described as a vitamin, L-carnitine is better thought of as a micronutrient which can be manufactured within the body. Dietary sources are important, however, because the amount of L-carnitine required by the body may sometimes exceed its ability to produce it.

The very name "carnitine" is derived from the Latin "carnus", which also of course gives us the term "carniverous". So it should be no surprise that red meat is the richest food source of this nutrient. 3 oz of beef steak, ground beef or mince will typically provide around 80 mg of L-carnitine; a similar serving of pork or bacon perhaps 20-25 mg. For those unable or unwilling to consume red meat, other sources are unfortunately much less productive. A half pint glass of milk may provide 8mg, fish 5mg and lean chicken a mere 3 mg. Non-animal foods are a relatively poor source of L-carnitine.

Conventional medical wisdom, however, is that even vegetarians should be able to produce enough L-carnitine from their diets to avoid symptoms of deficiency. But as always in matters of nutrition, the avoidance of deficiency is not at all the same thing as the achievement of optimum health.

So alternative practitioners and advocates of nutritional therapy are ever keen to stress the potential benefits of supplementation with the acetyl'L-carnitine form of this compound, which is much the most easily absorbed. Acetyl-L-carnitine has been hailed as an anti-oxidant, as a weapon in the treatment of both chronic and acute heart disease, as an aid to the production of energy, and as a boost for cognitive function.

Although the evidence is not yet clear cut, it has been suggested that acetyl-L-carnitine may play a role in reducing the production of the stress hormone, cortisol, an over supply of which is implicated as a factor in premature ageing and its associated diseases. It is believed that too much cortisol may suppress levels of dehydroepiandrosterone (DHEA), the key adrenal hormone, lavish levels of which are believed to help protect against the degenerative diseases commonly associated with ageing in the affluent West. Levels of DHEA begin to decline from about the early twenties onwards, just as levels of cortisol begin to rise, potentially creating a vicious circle of bodily decline.

Supplementing the diets of laboratory rats with acetyl-L-carnitine has been shown to increase tissue levels of L-carnitine, which are known to decline naturally with age, and to improve the metabolism of energy within the cell mitochondria. This research has generated considerable interest, although conventional medicine is not yet persuaded of its long term implications, if any, for human health, pending the results of the large scale clinical trials which are planned.

The evidence is much more clear cut, however, for L-carnitine's role in tackling heart disease. A number of studies have indicated that L-carnitine supplementation may be effective in restricting the damage to the heart muscle that typically follows a myocardial infarction (heart attack) and in improving the survival rates and exercise tolerance of those suffering from progressive heart failure or angina.

Research also suggests that L-carnitine supplementation in the form of acetyl-L-carnitine may slow the advance of Alzheimer's and other forms of dementia in the elderly. Nutritional therapists also claim that such supplementation can enhance memory and other cognitive function in healthy young adults; a claim that conventional medicine is of course reluctant to accept.

One potential problem with carnitine supplementation, however, is that absorption rates are relatively poor; only up to around 20% as opposed to perhaps 75% from L-carnitine from food sources. Acetyl-L-carnitine, however, is much the easiest to absorb, and supplements in this form are readily available and recommended by some authorities in quantities of between 500 and 1,000 mcg; so that even at low rates of absorption a plentiful supply may be obtained. As already noted, carnitine is a perfectly natural substance, manufactured in the body, and supplementation in these kind of quantities has not been shown to give rise to any side effects other than minor gastric upset in rare cases.

So as ever, the sensible and cost effective precaution appears to be to combine supplementation with a normal daily diet already well supplied with foods rich in acetyl-L-carnitine.