In common parlance the term carnitine denoted L-carnitine, which is a short chain carboxylic acid containing nitrogen. Carnitine has been identified for the first time in 1905 and the formula established definitively in 1927.

In nature, carnitine is present in meat and dairy products and is synthesized in the liver and kidney from the two amino acids methionine and lysine in the presence of iron, vitamin C, B1 and B6. Inside our body carnitine is concentrated at the muscular level (approximately 95%) and cardiac, while small amounts of carnitine are also present in kidney, liver and testes. The role of L-carnitine is to bind to fatty acids and allow the passage inside the mitochondria, where they are oxidized to produce energy. Furthermore, L-carnitine facilitates the conversion of pyruvate and lactate to acetyl coenzyme A and the production of pyruvate at the expense of milk, hence the hypothesis that L-carnitine plays, too, a feature limiting the accumulation of lactic acid . Other features are observed the stimulating action on cardiac contractility, hence its use in medicine in patients with heart problems, and function of peripheral vasodilation, which improves the flow and distribution of oxygen. For all these reasons it is considered that the incorporation of L-carnitine is useful and effective in sport, in order to improve his athletic performance (improvement of energy production, improved oxygenation of the muscles, better use of fat for energy , decreased production of lactic acid). In modern diets no shortages of L-carnitine, except in very rare cases, as in the presence of metabolic abnormalities that lead to a reduced or no ability to absorb or synthesize L-carnitine, in the presence of a strong demand, as pregnant or accretion (events, however, very rare and often associated with a reduced ability of the subject to synthesize or absorb L-carnitine), or in vegetarian diets vegan. In the latter case, in reality, there are conflicting reports, it appears that the vegan vegetarian diet is not, in itself, a cause of the lack of L-carnitine. The latter deficiency can cause muscle necrosis, myoglobinuria, myopathy from lipid accumulation, hypoglycemia, hyperammonemia and fatty liver disease with muscle pain, fatigue and confusion, while an overdose can cause nausea, vomiting and abdominal cramps. The adult subject has a capacity of biosynthesis ranging from 0.16 to 0.48 mg/kg body weight per day, the rate of synthesis, combined with the ability to reabsorption by the kidney is sufficient to fill the daily requirement. It's also good to consider that the ability to absorb L-carnitine, by the body varies greatly depending on the amount introduced daily foods and in which it is contained. It turns out, in fact, that people with diets low in meat (vegetarians) have a greater capacity to absorb L-carnitine, compared to subjects with diets high in foods with high content of L-carnitine. It also has a great importance in the total amount of ingested L-carnitine with high doses of L-carnitine are absorbed only minimally, metro smaller doses are absorbed almost completely, and this confirms the ability of vegetarians have a better capacity to absorb L-carnitine from foods naturally poor. It's important, then, to emphasize, as several studies have shown how the absorption of L-carnitine from food is higher than that achieved with the ingestion of oral supplements (63-75% vs. 14-20%).