Carnitine blood levels and muscle stores can become low, which may contribute to anemia, muscle weakness, fatigue, altered levels of blood fats, and heart disorders. Some studies have shown that supplementation of high doses of l-carnitine (often injected) may aid in anemia management. Sources
The form present in the body is l-carnitine, which is also the form present in food. Food sources rich in l-carnitine are animal products, particularly beef and pork. Red meats tend to have higher levels of l-carnitine. Adults eating diverse diets that contain animal products attain about 23-135 mg of carnitine per day. Vegans get noticeably less (about 10–12 mg) since their diets lack these carnitine-rich animal-derived foods. Approximately 54% to 86% of dietary carnitine is absorbed in the small intestine, then enters the blood. Even carnitine-poor diets have little effect on total carnitine content, as the kidneys conserve carnitine. In general, omnivorous humans each day consume between 2 and 12 µmol kg−1 of body weight, accounting for 75% of carnitine in the body. Humans endogenously produce 1.2 µmol kg−1 of body weight of carnitine on a daily basis, accounting for 25% of the carnitine in the body. Strict vegetarians obtain little carnitine from dietary sources (0.1 µmol kg−1 of body weight daily), as it is mainly found in animal-derived foods.L-Carnitine, acetyl-l-carnitine, and propionyl-l-carnitine are available in dietary supplement pills or powders, with a daily amount of 0.5 to 1 g considered to be safe.
HTML is then cleaved by HTML aldolase (a pyridoxal phosphate requiring enzyme), yielding 4-trimethylaminobutyraldehyde (TMABA) and glycine. TMABA is then dehydrogenated into gamma-butyrobetaine in an NAD+-dependent reaction, catalyzed by TMABA dehydrogenase. Gamma-butyrobetaine is then hydroxylated by gamma butyrobetaine hydroxylase (a zinc binding enzyme) into l-carnitine, requiring iron in the form of Fe2+.Carnitine is involved in transporting fatty acids across the mitochondrial membrane, by forming a long chain acetylcarnitine ester and being transported by carnitine palmitoyltransferase I and carnitine palmitoyltransferase II. Carnitine also plays a role in stabilizing Acetyl-CoA and coenzyme A levels through the ability to receive or give an acetyl group. Tissue distribution of carnitine-biosynthetic enzymes
The tissue distribution of carnitine-biosynthetic enzymes in humans indicates TMLD to be active in the liver, heart, muscle, brain and highest in the kidney. HTMLA activity is found primarily in the liver. The rate of TMABA oxidation is greatest in the liver, with considerable activity also in the kidney. Carnitine shuttle system
The free-floating fatty acids, released from adipose tissues to the blood, bind to carrier protein molecule known as serum albumin that carry the fatty acids to the cytoplasm of target cells such as the heart, skeletal muscle, and other tissue cells, where they are used for fuel.