Derived from an amino acid, it is present in almost every cell in the body.
Its name is derived from the Latin carnus or meat, since the compound was isolated from meat. It is the generic term for a number of compounds including L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine.
Carnitine plays a critical role in energy production. It transports long-chain fatty acids to the mitochondria so that they can be burned and thus produce energy.
It also transports the toxic compounds generated from this cellular organelle to prevent their accumulation. Given these key functions, carnitine is concentrated in tissues such as skeletal and cardiac muscle that use fatty acids as dietary fuel.
The body produces enough carnitine to meet the needs of most people. For genetic or medical reasons, some individuals cannot earn enough, which is why carnitine is a conditionally essential nutrient for them.
Healthy children and adults do not need carnitine from food or supplements, as the liver and kidneys produce sufficient amounts of the amino acids lysine and methionine to meet daily needs.
What Foods Provide Carnitine?
Animal products such as meat, fish, poultry, and milk are the best sources.
In general, the redder the meat, the higher the carnitine content. Dairy products contain carnitine mainly in the whey fraction.
Carnitine comes in two forms, known as D and L, which are mirror images (isomers) of each other. Only L-carnitine is active in the body and it is the form found in food.
Foods high in carnitine include:
- Beef steak, cooked, 4 ounces contains 56 to 162 milligrams (mg).
- Milk, 1 cup contains 8 mg.
- Chicken breast, cooked, 4 oz. Contains 3 to 5 mg.
- Cheese, cheddar cheese, 2 oz. Contains 2 mg.
Adults whose diets are rich in red meat consume on average about 60 to 180 mg of carnitine per day. A vegan diet normally provides between 10 and 12 mg per day.
Studies suggest that the body absorbs 54% to 86% of dietary carnitine into the bloodstream, but only 14% to 18% when taken as a supplement.
Supplemental sources of carnitine
L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine are available over the counter as dietary supplements. Carnitine is often promoted as an aid to losing weight, improving exercise performance, and enhancing feelings of well-being.
It is also a drug approved by the Food and Drug Administration to treat primary and certain secondary carnitine deficiency syndromes.
Adults who eat mixed diets that include red meat and other animal products get about 60-180 milligrams of carnitine per day.
Vegans get considerably less (around 10-12 milligrams) as they avoid animal-derived foods. Most (54-86%) of dietary carnitine is absorbed in the small intestine and enters the bloodstream.
The liver and kidney generally produce enough carnitine in the human body, so it is not necessary to supplement with food or supplements. There is no recommended daily intake.
However, genetic or medical reasons can cause some people to produce too little.
Primary systemic carnitine deficiency can occur when the protein that is responsible for carrying carnitine into cells undergoes a genetic change. This deficiency causes problems with food processing.
This rare condition can lead to:
- Low plasma carnitine.
- Progressive cardiomyopathy or heart muscle disease.
- Skeletal myopathy.
- Weak muscles in the hips, shoulders, arms, legs, neck, and jaw muscles.
Without treatment, it is fatal. Symptoms gradually worsen from infancy to early adulthood.
To treat it, the doctor will prescribe pharmacological doses of carnitine, to correct the problems of cardiomyopathy and muscle weakness.
When can a carnitine deficiency occur?
There are two types of carnitine deficiency states. Primary carnitine deficiency is a genetic disorder of the cellular carnitine transporter system that usually manifests by the age of five with symptoms of cardiomyopathy, skeletal muscle weakness, and hypoglycemia.
Secondary carnitine deficiencies can occur due to certain disorders, such as chronic kidney failure , cancer, and aging.
Current controversies about carnitine
Carnitine has been studied extensively because it is important for energy production and is a well-tolerated and generally safe therapeutic agent.
Researchers prefer to use acetyl-L-carnitine in research studies because it is better absorbed in the small intestine than L-carnitine and more efficiently crosses the blood-brain barrier (i.e., enters brain tissue)
There is some evidence to support the use of carnitine in medicine. It is a popular supplement among athletes, but more research is needed to confirm its effectiveness in enhancing performance.
As an antioxidant, carnitine fights harmful free radicals, which cause severe damage to cells.
Health conditions that carnitine can be used to treat include heart failure or heart attack, angina, and diabetic neuropathy.
Here are some diseases or conditions that could be treated with carnitine:
Some athletes take carnitine to improve performance. However, twenty years of research does not find consistent evidence that carnitine supplements can improve exercise or physical performance in healthy subjects, in doses ranging from 2-6 grams per day administered for 1 to 28 days.
A decrease in mitochondrial function is believed to contribute to the aging process. Carnitine may be involved because its concentration in tissues decreases with age and therefore reduces the integrity of the mitochondrial membrane.
Studies suggest that acetyl-L-carnitine supplements can improve mental function and reduce impairment in older adults with mild cognitive impairment and Alzheimer’s disease.
Cardiovascular and peripheral arterial disease
Several studies have examined the effectiveness of supplemental carnitine in treating cardiac ischemia (restriction of blood flow to the heart) and peripheral arterial disease (the most important symptom of which is poor circulation in the legs, known as intermittent claudication).
Because carnitine levels are low in defective heart muscle, supplemental amounts could counteract the toxic effects of free fatty acids and improve carbohydrate metabolism.
In short-term studies, carnitine has had anti-ischemic properties when administered orally and by injection.
Research indicates that carnitine may improve the performance of skeletal muscles in the leg. L-carnitine, when administered for up to 1 year, could have beneficial effects on the cardiovascular system in certain settings.
In one study, treatment with carnitine supplements improved fatigue in the majority of chemotherapy-treated subjects and restored normal blood levels of carnitine.
In another trial, terminal cancer patients supplemented with carnitine experienced less fatigue and improved mood and quality of sleep. In both studies, the majority of the subjects were carnitine deficient before taking the supplements.
Type 2 diabetes
Insulin resistance, which plays an important role in the development of type 2 diabetes, may be associated with a defect in the oxidation of fatty acids in the muscle.
Early research suggests that intravenous L-carnitine supplementation may improve insulin sensitivity in diabetics by lowering muscle fat levels and may lower blood glucose levels by more rapidly increasing its oxidation in the muscles. cells.
A recent analysis of two multicenter clinical trials of subjects with type 1 or type 2 diabetes found that acetyl-L-carnitine treatment for one year provided significant relief of nerve pain and improved vibration perception in those with diabetic neuropathy.
Treatment was most effective in subjects with short-term type 2 diabetes.
HIV and AIDS
The human immunodeficiency virus (HIV) causes a decrease in the number of lymphocytes (a type of white blood cell), resulting in acquired immunodeficiency syndrome (AIDS).
This syndrome can represent the mitochondrial toxicity caused by HIV infection and the antiretroviral drugs used to treat it, and can induce a carnitine deficiency that limits the metabolism of mitochondrial fats. The molecular mechanisms by which this occurs are poorly understood.
Preliminary research provides conflicting findings but suggests that intravenous and oral carnitine supplementation in HIV-infected individuals can delay lymphocyte death (which in turn can slow HIV progression), reduce neuropathy, and favorably affect lipid levels in the blood.
End-stage renal disease and hemodialysis
Carnitine homeostasis among individuals with kidney disease can be substantially affected by several factors, particularly reduced synthesis and increased elimination of the compound by the kidneys, as well as lower food intake due to poor appetite and consumption of fewer source products. animal.
Many patients with end-stage renal disease, particularly those on hemodialysis, become insufficient for carnitine.
Carnitine levels in the blood and muscle stores are low, which can contribute to anemia, muscle weakness, fatigue, altered levels of fats in the blood, and heart disorders.
Numerous studies suggest that high doses of supplemental carnitine (often injected) in maintenance hemodialysis patients can correct some or all of these symptoms, although most involve a small number of patients and are not double-blind trials.
A recent meta-analysis of these studies concludes that carnitine supplements may help anemia management but not blood lipid profiles, and that their effects on exercise capacity or cardiac stability are inconclusive.
The carnitine content of seminal fluid is directly related to sperm count and motility. Suggesting that the compound could be of value in treating male infertility.
Several studies indicate that carnitine supplementation can improve sperm quality.
Findings published in the journal Thrombosis Research looked at the efficacy, safety, and tolerability of propionyl-L-carnitine (PLC) given to patients with a condition known as intermittent claudication.
Intermittent claudication can cause pain when walking or running, as damage or narrowing of an artery leads to poor blood supply.
As therapy, carnitine is generally safe and well tolerated, but carnitine supplements can cause some unwanted effects.
According to the National Institutes of Health in the USA, an intake of 3 grams of carnitine per day leads to:
- Abdominal cramps and diarrhea.
- A “fishy” body odor.
Other sources suggest that an increase in appetite and a rash may occur.
The most common side effects include:
- Muscle weakness in uremic patients.
- Seizures in those who already have seizure disorders.
People should be especially sure to inform their doctor before using it as a supplement if they have:
- Kidney disease
- High blood pressure.
Carnitine can interact with phenobarbital, valproic acid, phenytoin, carbamazepine, and some antibiotics, but there is no evidence that these can lead to a deficiency.
The Linus Pauling Institute recommends that anyone deciding to take carnitine supplements should consider acetyl-L-carnitine at 500 mg to 1,000 mg per day.
Before taking any supplement, it is always advisable to speak with a doctor.
Carnitine and drug interactions
Carnitine interacts with pivalate-conjugated antibiotics, such as pivampicillin, which are used in the long-term prevention of urinary tract infections.
Chronic administration of these antibiotics increases the excretion of pivaloyl-carnitine, which can lead to carnitine depletion. However, although tissue carnitine levels may be low enough to limit fatty acid oxidation, no disease due to deficiency has been reported.
Treatment with the anticonvulsants valproic acid, phenobarbital, phenytoin, or carbamazepine has been shown to significantly reduce blood levels of carnitine.
In addition, the use of valproic acid with or without other anticonvulsants can cause hepatotoxicity and increase plasma ammonia concentrations, leading to encephalopathy.
This toxicity can also occur after an acute overdose of valproic acid. Administration of L-carnitine can help treat valproic acid toxicity in children and adults, although the optimal regimen has not been identified.