The bioavailability of L-carnitine
The homeostasis of L-carnitine is maintained through biosynthesis, efficient reabsorption in the kidneys and food intake, particularly from meat and dairy products. The physiological range of different L-carnitine concentrations in various tissues is maintained by complex transporter systems. The biosynthesis of L-carnitine from the amino acids lysine and methionine proceeds in the liver, kidney and testis, with butyrobetaine (GBB) being an intermediate precursor. It has been estimated that in the case of a non-vegetarian diet, only about 25% of the necessary L- carnitine is biosynthesised, and 75% is ingested from food. Interestingly, the blood plasma concentration in women is about 20% lower than in men. Additionally, in vegetarians, the L-carnitine concentration in the blood serum is 20- 30% lower than that in the reference population.