L-CARNITINE - General Discussion

FUNCTIONS AND USES

Energy Production

L-carnitine's most important function is the transport of fatty acids into the muscles, where they can be burned for energy. Because fatty acids are a major fuel source for working muscles, carnitine deficiency can reduce the amount of energy available to the body.

L-carnitine levels in muscles are increased by physical training. Moreover, supplementation appears to build stamina and endurance, and may therefore enhance exercise performance, particularly in people with low levels of this nutrient. Supplementation appears to be most beneficial in well-conditioned individuals and athletes, whom it helps, resist fatigue. Carnitine is also often prescribed for individuals who suffer from muscle fatigue due to conditions such as fibromyalgia and chronic fatigue syndrome.

Cardiovascular Disease

Just as L-carnitine plays an essential role in transporting fatty acids into other muscles for energy, it is needed to transport these substances into the heart, the most important muscle in the body. Understandably, much of the research concerning L-carnitine has focused on its use in the treatment of heart disease.

Approximately 60 percent of the energy for the heart muscle is supplied by fatty acids. Thus, myocardial (heart muscle) L-carnitine deficiency has been found to be associated with myopathic heart disease, aging, diabetes, diphtheria, and chronic heart failure. L-carnitine supplementation has been shown to help lessen the impairment of heart muscle function associated with these conditions.

L-carnitine supplementation appears to benefit the heart in other ways, as well. Human studies have also shown that carnitine supplementation improves exercise tolerance and heartbeat regularity in patients with angina pectoris; significantly reduces the extent of cardiac necrosis (cell death) in patients hospitalized for heart attack; decreases the incidence of heart failure and reduces the need for pacemaker transplants in patients with heart disorders; and reduces the number of deaths due to myocarditis (inflammation of heart muscle tissue). In addition, carnitine has been used successfully to treat hypertriglyceridemia (elevated blood triglycerides), a risk factor for heart disease. It also increases levels of high-density lipoproteins (HDLs), which have been associated with a reduced risk of heart disease.

The Nervous System

L-Carnitine may also be important for healthy brain function, since it appears to influence the metabolism of several neurotransmitters-chemicals that facilitate the sending of signals from one nerve fiber to another. In a study involving people with Alzheimer's disease, the progression of the disease was significantly reduced in those receiving 2 grams per day of acetyl-L-carnitine, a particular form of carnitine, orally for one year.

Detoxification

L-carnitine also seems to have some antioxidant properties, as well as the ability to help detoxify certain drugs. For example, it appears to protect the heart muscle from the damage caused by Adriamycin (doxorubicin hydrochloride), a drug used in cancer treatment.

RDIs AND DEFICIENCIES

Vegetarians are at particular risk for low carnitine levels for two reasons. First, L-carnitine can be obtained only from animal foods. Second, certain nutrients-vitamin C, niacin, vitamin B6, iron, and the amino acid L-lysine-are essential for the synthesis of carnitine. Because cereal grains such as corn, wheat, and rice, mainstays of many vegetarian diets are low in L-lysine, a vegetarian's ability to synthesize carnitine may be compromised. The cooking or toasting of these grains destroys L-lysine entirely.

L-carnitine loss has been documented in patients receiving dialysis. This loss has been related to the complications these patients often face, such as high blood lipids, cardiomyopathy (any disease of the heart muscle), muscle loss, and muscle cramps. Treatment with oral L-carnitine has been shown to replace lost carnitine and improve these complications.

Although as adults we can synthesize L-carnitine, the diet seems to be an infant's only source of this amino acid. In the case of specific genetic disorders, such as organic aciduria, carnitine supplementation is necessary.

Since L-carnitine can both be found in foods and manufactured in our bodies under normal conditions, there is no RDI for this nutrient.

Food Sources: L-carnitine is found only in animal foods. We can synthesize carnitine provided that we have enough L-lysine, which is predominantly found in animal foods as well as the other nutrients required for its synthesis.

SUPPLEMENTS

The L forms of this nutrient, such as L-carnitine and acetyl-L-carnitine, are the most biologically active forms, and are the only forms found in foods and synthesized by our bodies. When carnitine is chemically synthesized both the L and D forms are produced. Although supplements generally contain the L forms, be sure to avoid ones containing the D form, since they may actually inhibit the action of L-carnitine in metabolic processes.

L-carnitine and acetyl-L-carnitine are available as supplements at this time. Other forms of carnitine are generally used for research purposes, but may eventually find their way into the supplement market.

OPTIMUM DAILY INTAKE

There is no Optimum Daily Intake for carnitine. Studies have generally used 1 to 5 grams of carnitine orally. Higher levels have been used in studies that administered the supplement intravenously.

Remember: If you have a medical condition, please consult your physician before taking supplements.

TOXICITY AND ADVERSE EFFECTS

There is no known toxicity of carnitine, even with very high doses. In studies in which 5 to 6 grams were taken orally, some gastrointestinal side effects, such as bloating and flatulence, were noted. These can be avoided by starting with smaller doses and gradually increasing the dose over time.

CARNITINE (L-carnitine) A nutrient required for fat oxidation and energy production. Carnitine helps transport FATTY ACIDS into mitochondria, the cellular structure specialized for fuel oxidation. Carnitine may be necessary for the oxidation of certain amino acids (VALINE, ISOLEUCINE and LEUCINE) for energy. The daily requirement for L-carnitine for health is unknown. The body synthesizes L-carnitine from two essential amino acids, LYSINE and METHIONINE. The rate may be inadequate for: kidney patients on hemodialysis; patients with liver failure; strict VEGETARIANS; premature and low birth-weight infants; pregnant or lactating women; children with genetic predisposition to carnitine deficiency or who experience infection or malnutrition. Breast milk contains a high level of L-carnitine to nurture the infant, and it may be an essential nutrient for the newborn.

Carnitine deficiency causes muscle weakness, severe confusion, angina, and high blood lipids, including CHOLESTEROL. Carnitine deficiency is also linked to cardiac enlargement and congestive heart failure. Fatty acid oxidation is a major source of energy for the heart muscle, and carnitine deficiency causes extreme metabolic impairment. The normal heart stores carnitine, but if it does not receive adequate oxygen, carnitine levels drop. Supplementation with carnitine raises heart carnitine levels, allowing the heart to use a limited oxygen supply more efficiently. Thus carnitine has been used effectively to treat atherosclerosis, angina and coronary heart disease. Carnitine may reduce blood fat and LOW-DENSITY LIPOPROTEIN (LDL, undesirable cholesterol) and increase HIGH-DENSITY LIPOPROTEIN (HDL, desirable cholesterol). Carnitine also decreases blood fat. It may help patients with angina and CARDIOVASCULAR DISEASE, and with some types of muscle disease. A derivative of carnitine called acetyl L-carnitine appears to be neuroprotective. Supplementing with acetyl L-carnitine may improve cognitive defects associated with forms of senility and age-related depression. Low carnitine levels may be linked to chronic fatigue symptoms.

Good sources of carnitine are red meats and dairy products like milk. Tempeh and avocados contain some carnitine; however, most vegetables, fruits and grains are poor sources. Most soy-based infant formulas are supplemented with carnitine. While the naturally occurring form of carnitine, (L-carnitine) appears to be safe, high doses of synthetic carnitine (D, L-carnitine), a mixture of isomers, for many weeks can cause progressive weakness and atrophy of certain muscles. Symptoms disappear when supplementation with the mixture ceases.