Carnitine is the compound responsible for the transport of long-chain fatty acids in the cellular units of energy production: the mitochondria. Since carnitine can be synthesized from the essential amino acid lysine, many nutritionists and researchers believe it should not be considered a vitamin.
For others, however, since niacin can be synthesized from the essential amino acid tryptophan, it is considered a vitamin.
Carnitine was isolated from meat extracts in 1905 but its chemical structure was only defined in 1932.
However, despite extensive studies conducted in the 1930s, the role of carnitine remains a mystery until about 50 years after its discovery.
In 1952, a group of researchers discovered that carnitine is a growth factor for Tenebrio molitor and has since been called vitamin Bt.
When it was discovered that other species of organisms depended on carnitine, its role in the organism was re-examined and it was soon discovered that it is essential for the breakdown of fats to produce energy.
Its importance lies in the fundamental role it plays in the transport of fatty acids in the mitochondria.
Since the carrier molecule of fatty acids, acyl-CoA, cannot cross the cell membrane, a carnitine deficiency causes a reduction in the concentration of fatty acids in the mitochondria and, consequently, a reduced production of energy.
Fatty acids need to be transferred from CoA to carnitine.
The acyl-camitin molecule transports the fatty acid to the mitochondrial surface of the inner mitochondrial membrane where it releases it to be transformed into energy.
Carnitine performs many other physiological functions including the conversion of keto acids to branched chain amino acids: valine, Ieucine and isoleucine, an extremely important function during fasting and exercise.
Food sources Meat and dairy are the main dietary sources of carnitine. In general, the redder the meat, the higher the carnitine content. Cereals, nuts and vegetables contain little or are completely free of it. Preliminary studies indicate that an average daily diet contains 5 to 100 mg5.
Most of it, however, is synthesized from the essential amino acid lysine with the help of another essential amino acid (methionine), three vitamins (vitamin C, niacin and vitamin B6) and iron.
Of course, a deficiency in any of these nutrients produces a carnitine deficiency. The final stage of carnitine synthesis occurs only in the liver, kidneys and brain, as the butyrobetaine hydroxylase enzyme, necessary for the final reaction, is present only in these tissues.
This enzyme is largely responsible for controlling the synthesis of carnitine, heart muscle, skeletal muscle tissue and many other tissues. Specific proteins for carnitine transport have been identified in the heart, skeletal muscle tissue, liver and kidneys.
They are proteins that facilitate the transfer of carnitine from the blood to the cells through carrier-mediated transport mechanisms.
This active transport mechanism allows tissues to concentrate carnitine at levels even 10 times higher than those found in plasma.
In children, the activity of the enzyme of the final stage of carnitine synthesis is only 12% of the normal average for adults.
From 2 and a half years of age, activity is 30% of the average adult one, which is only reached around the age of 15.
These data underline the importance of carnitine contained in breast milk in infant nutrition.
The initial concentration of carnitine in newborns depends on that present in the mother's organism.
The concentration in the umbilical and fetal cord blood is higher than that of the maternal blood, which indicates that the placenta is actively working to concentrate carnitine in the fetus, the synthesis of which is not yet completely efficient.
In pregnant women, in which a reduced synthesis of carnitine is suspected, it may be necessary to resort to supplements in order to ensure an adequate concentration in both the fetus and the mother's tissues.
Blood carnitine levels are usually lower in pregnant women than in non-pregnant women due to the increased needs of the fetus.
The newborn is almost entirely dependent on external sources of carnitine.
Breast-fed infants have the best chance of achieving optimal carnitine concentrations because the bioavailability of carnitine obtained from breast milk is significantly greater than that of milk-based infant formulas.
The administration of carnitine in premature babies has two important purposes: weight gain and growth.
Signs and symptoms of deficiency
The first cases of carnitine deficiency in humans were described in 1973.
It has always been thought that one could synthesize the necessary amount of carnitine, ingest it sufficiently with food or satisfy the need through a combination of these two modalities.
Carnitine deficiency are classified into two main groups: systemic (in the whole organism) deficiency of carnitine and myopathic deficiency (in the muscles).
Diagnosis of systemic deficiency can be made using serum or urine samples while the myopathic requires skeletal muscle tissue biopsy.
Carnitine deficiency: consequences
- Deficiency in iron, ascorbic acid, pyridoxine and niacin
- Genetic defect of carnitine biosynthesis
- Insufficient intestinal absorption of carnitine
- Liver or kidney disorders resulting in reduced carnitine synthesis
- Increased metabolic losses of carnitine by catabolism, reduced reabsorption in the renal tubule or genetic defec
- Defective transport of carnitine from synthetic tissues to tissues of maximum utilization Increased need for carnitine due to a high-fat diet, metabolic stress or disease.
In adults, compensation mechanisms seem to be activated that allow an adaptation that appears in fasting, diabetes, diets rich in fat and in other situations of secondary carnitine deficiency.
It seems that children are not able to adapt to low levels of camitina as well as adults.
Several cases of carnitine deficiency have been reported in children whose clinical picture resembled that of Reye's syndrome: acute cerebral edema associated with impaired liver function due to fat accumulation.
The clinical picture of secondary carnitine deficiency in children includes: loss of muscle tone slowdown in growth, recurrent infections cerebral edema, hypoglycemia and heart disorders.
Carnitine supplements can improve the utilization of fat as an energy source and have a positive effect in the treatment of those numerous conditions in which there is impaired lipid utilization and energy production.
The carnitine is available in different forms.
Its good to always make use of the camitina in L form (left-handed), alone or linked to acetic or propionic acid.
The best form depends on the purpose: in Alzheimer's disease and to achieve an effect on brain tissue, it appears that the best form is L-acetylcarnitine; in angina the best choice could be L-propionylcarnitine as the myocardium seems to prefer it to L-acetylcarnitine.