[Carnitine: vitamin or doping?].

Abstract

Carnitine (L-trimethyl-3-hydroxy-4-ammonio-butyrate) is a chemically simple substance with essential functions in energy metabolism. Most of the carnitine needed is ingested by the diet, in particular by meat and dairy products. The rest is biosynthesized, starting from the amino acids lysine and methionine. In humans, carnitine biosynthesis is just sufficient to avoid symptomatic carnitine deficiency, when carnitine intake by the diet is absent or low. Carnitine can therefore not be regarded as a vitamin. Primary carnitine deficiency is mostly due to increased renal carnitine excretion because of a defective carnitine transport in the proximal tubule. Secondary carnitine deficiency can develop due to increased excretion of acylcarnitines in patients with organic acidurias or after longterm treatment with pivaloyl-esters or other drugs. Symptomatic carnitine deficiency should be treated with pharmacological doses of carnitine. There are no studies supporting the concept that acute administration of carnitine is associated with increased physical performance in athletes. Acute ingestion of carnitine by athletes is not doping, but cannot be advised from a scientific standpoint. So far, there are no randomized controlled studies investigating the effect of chronic carnitine administration on physical performance in athletes.