Carnitine (vitamin Bt)

Carnitine is a non-essential amino acid produced in the liver, brain and the kidneys from the essential amino acids methionine and lysine. Carnitine is the generic term for a number of compounds that include L-carnitine, L-acetylcarnitine, acetyl-L-carnitine, and L-propionyl carnitine. Carnitine can be synthesised within the body from lysine or methionine. As with all amino acids used directly in the metabolism, carnitine exists in the left-handed form. This isomer is expressed as L-carnitine, as it is usually marketed. Carnitine is eaten in the diet in red meats and dairy products, including breast milk, and is also made in the body from breaking down muscle protein and converting it to carnitine.

Carnitine is a nutrient responsible for the transport of long-chain fatty acids into the energy-producing centers of the cells (known as the mitochondria). Carnitine plays a critical role in metabolizing a number of other important substances as well, which helps to explain why it holds promise for so many disorders. Carnitine transports fats into the mitochondria, the cellular powerhouse, where these fats are converted into an energy source for the body. Our heart and skeletal muscle tissue rely on fat utilization as a source of energy, and also to spare glycogen.

Carnitine helps the body convert fatty acids into energy, which is used primarily for muscular activities throughout the body. The body produces carnitine in the liver and kidneys and stores it in the skeletal muscles, heart, brain, and sperm. Carnitine can also act as an antioxidant and appears to play a role in maintaining the health of nerves and protecting the liver and kidneys from the toxicity of drugs.

Carnitine (vitamin Bt) functions, uses, and health benefits

Carnitine helps transport fatty acids to the powerhouse of the cell. Fatty acids are the main fuel source for heart and skeletal muscle. Long-chain fatty acids require l-carnitine to transport them across the inner membranes of the mitochondria, wherein their metabolism produces bioenergy. L-carnitine can remove short-chain and medium-chain fatty acids from the mitochondria in order to maintain coenzyme A levels in these organelles. L-Carnitine also facilitates the metabolism of carbohydrates and enhances the rate of oxidative phosphorylation. L-Carnitine works synergistically with CO-Q10, an antioxidant and energy co-factor that is found in the inner membrane of the mitochondria.

Carnitine plays a critical role in metabolizing a number of other important substances as well, which helps to explain why it holds promise for so many disorders. Carnitine mediates the transport of medium/long-chain fatty acids across mitochondrial membranes, facilitating their oxidation with subsequent energy production. Carnitine may have neuroprotective effects. This means that the strong antioxidant properties of acetyl-L-carnitine may help to prevent oxidative damage to nerve cells that are important for brain functioning.

The strongest evidence for the use of supplemental L-carnitine may be in the management of cardiac ischemia and peripheral arterial disease. It may also more generally be indicated for cardioprotection. It lowers triglyceride levels and increases levels of HDL-cholesterol in some. It is used with some benefit in those with primary and secondary carnitine deficiency syndromes. There is less evidence to support arguments that carnitine is indicated in liver, kidney and immune disorders or in diabetes and Alzheimer's disease.

Carnitine is used for a small percentage of people who are at risk of liver damage from AEDs and is used for children with multiple seizure types who are taking multiple AEDs. Carnitine is used in emergency situations where there is liver damage caused by valproate, or in cases of valproate overdose. It is used in rare diseases involving problems of the transport of carnitine into the mitochondria.

L-carnitine has been marketed as a weight loss supplement, because the primary function of carnitine in human cells is to burn fat as a source of energy. Carnitine supplementation may actually help increase energy, burn fat more efficiently and may improve heart and liver health all at the same time.

Carnitine is recommended as a daily supplement to help maintain blood lipid profile and promote fatty acid utilization within heart muscle. People who take l-carnitine supplements soon after suffering a heart attack may be less likely to suffer a subsequent heart attack, die of heart disease, experience chest pain and abnormal heart rhythms, or develop congestive heart failure. Some studies have shown Carnitine may reduce the pain and complications of lack of oxygen to the heart and improve exercise tolerance in people with existing heart disease.

The function of carnitine is to help the body use stored fat as fuel. Carnitine is helpful for improving exercise performance. Supplementation with carnitine has been said to enhance lipid oxidation, increase VO2max and decrease the accumulation of lactic acid during exercise.

Carnitine reduces the incidence of angina and cardiac arrythmias as well as reduces the need for anti-angina and anti-arrythmic medications.

Acetyl-L-carnitine may be indicated for use in cases of mild Alzheimer's disease, dementia, Down's syndrome, recovery from stroke and for the management of various neuropathies.

Carnitine (vitamin Bt) dosage, intake, recommended daily allowance (RDA)

Carnitine is not an essential amino acid and, since it is not a vitamin or a mineral, no RDA or dietary reference intake (DRI) values have been established. The L-isomer of carnitine (L-carnitine) is the only physiologically useful form of carnitine. Recommended doses of l-carnitine supplements vary depending on the health condition being treated. The normal recommended dose appears to be 500 milligrams (MG) to 1,000 mg per day. Then gradually work up to 2 to 4 grams (2,000 to 4,000 mg) per day.

Typical doses of supplemental acetyl-L-carnitine are between 500 mgs to 2 gms daily in divided doses. Doses of 2 to 6 grams per day are typically recommended for cardiovascular, sports performance and weight loss benefits. Infant formulas (including total parenteral nutrition solutions) that do not contain carnitine should be supplemented with carnitine to the levels found in human milk, 11.3 mg/L (70 mmol/L).

Sources of carnitine

Dietary sources of carnitine include foods of animal origin, such as meat and dairy products. Red meat (particularly lamb) and dairy products are the primary sources of carnitine. Carnitine can also be found in fish, poultry, tempeh (fermented soybeans), wheat, asparagus, avocados, and peanut butter. Cereals, fruits, and vegetables contain little or no carnitine. Carnitine can be manufactured in the body provided the requisite vitamins and minerals are also present. A typical Western diet supplies about 100mg of carnitine per day. It is found mostly in red meats and dairy products. Plant foods are not good sources of carnitine. In general, healthy adults do not require dietary carnitine as carnitine stores are replenished through endogenous synthesis from lysine and methionine in the liver and kidneys.

Carnitine deficiency

There are two types of carnitine deficiency, primary and secondary. In both primary and secondary carnintine deficiencies, increased dietary intake and supplements of carnitine can be beneficial. Although the exact mechanism is unknown, it is thought that flooding the body with high concentrations of carnitine assures that some carnitine are able to get into the cells. Carnitine deficiency occurs as a primary genetic defect of carnitine transport and secondary to a variety of genetic and acquired disorders. A person with primary carnitine deficiency has very low levels of carnitine in the blood due to a faulty carnitine transporter which prevents carnitine from getting into the cells where it is needed.

The secondary form of carntine deficiency can arise secondary to metalobic disorders in the mitochondria. Blockage of metabolic pathways in the mitochondria leads to a build-up of acyl compounds. Infants are particularly susceptible to carnitine depletion, because the demands of tissue accretion associated with rapid growth exceed the ability of the infant to synthesize carnitine.

Carnitine is a protein found in all tissues and is essential in mammalian energy metabolism. It facilitates the entry of long-chain fatty acids into the mitochondria of the cells thereby delivering substrate, which are acted upon by enzymes, for oxidation and subsequent energy production. Humans obtain it from food, including red meat, milk and milk products; it is also produced by the body from the dietary amino acids, lysine and methionine. Most carnitine (90-98%) is stored in skeletal and cardiac muscles, at levels roughly 10 times higher than the levels found in the blood.

L-Carnitine has a direct positive effect on heart muscle function. It can improve the energy metabolism of heart muscle cells which have not received enough oxygen. It has been shown to strengthen the force of contraction and heart rate. It is also involved in mental function because it transports essential fatty acids to the brain. Therefore, L-Carnitine deficiency can lead to fatigue and weakness.

Sick children with metabolic disorders often rely on total parenteral nutrition (TPN) that is not routinely supplemented with carnitine, and a deficiency can develop within days or weeks. A chronic metabolic disorder, such as maple syrup urine disease (MSUD) which requires a special low protein diet, makes these infants and children even more vulnerable.

Carnitine plays a very important role in controlling the action of heart. Carnitine is an amino acid that is required for the transport of long-chain fatty acids into the mitochondria, the site of beta-oxidation of fatty acids. About 25 percent of the carnitine required by the body is produced by the liver and kidneys, while the rest is derived from dietary intake, primarily from red meat, poultry, fish, and dairy products. Most of the carnitine in the body is located in the voluntary and cardiac muscles.

Carnitine functions in the body as a carrier of fatty acids to the energy centers in muscles (mitochondria). A deficiency of carnitine results in decreased energy available to muscle, causing muscle weakness and low muscle tone. Energy is required for the growth of muscle and for weight gain, so the child with carnitine deficiency often fails to thrive. A deficiency can affect cardiac muscle and result in poor cardiac contractions (cardiomyopathy). This leads to heart failure which may respond dramatically to carnitine therapy.

Carnitine deficiency can cause serious heart and liver problems. This may occur in inborn errors of metabolism, renal tubular dysfunction (Fanconi's syndrome), chronic renal failure, or with valproic acid (Depakene, Depakote) and zidovudine (Retrovir). In children, low concentrations of carnitine have been reported in: malnutrition, glutamic aciduria, Spanish oil poisoning syndrome, Duchenne muscular dystrophy, and low birth weight infants receiving total parenteral nutrition.

Both systemic and myopathic types are probably genetic and siblings may be affected. Myopathic carnitine deficiency resents with a lactic acidosis possibly arising because of an increased dependence on carbohydrate metabolism for energy. Plasma carnitine may be slightly low or normal but musccle carnitine is low. It is not known whether the defect is increased leakage of carnitine from muscle or decreased uptake. Muscle biopsy shows a gross lipid storage myopathy. Some patients benefit from corticosteroid therapy. Patients with systemic carnitine deficiency have a progressive neuromuscular disorder with nausea and vomiting. Occasionally, hypoglycaemia and dicarboxylic aciduria have also been reported. The condition may progress to coma and death.

Carnitine deficiency can result from a reduced capacity for its biosynthesis, subnormal levels of carnitine palmitoyltransferase; alteration in cellular mechanisms for carnitine transport, excess loss of carnitine due to diarrhea, diuresis, or hemodialysis, increased requirements for carnitine in states of ketosis and high demand for fat oxidation; and inadequate intake during long-term TPN. Among people with diabetes, carnitine deficiency is more likely to be found in persons experiencing complications of diabetes (such as retinopathy, hyperlipidemia, or neuropathy), suggesting that carnitine deficiency may play a role in the development of these complications. A carnitine deficiency can also result from oxygen deprivation which can occur in some heart conditions.