Carnitine is present in almost every cell in the body. It plays a crucial role in energy production, as it is responsible for transporting fatty acids to the mitochondria.

Mitochondria exist inside every cell in the body. They produce the energy that cells need to function.

The body creates carnitine from the amino acids lysine and methionine. Scientists first isolated it from meat. As a result, takes its name from the Latin word for meat.

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 improving performance.

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Carnitine is a popular supplement amongst athletes.

Carnitine has two functions.

A part of carnitine transports long-chain fatty acids into mitochondria. They are burned there, or oxidized, to produce energy.

Another part transports waste and toxic compounds out of the mitochondria, and this prevents unwanted substances from building up.

Skeletal and cardiac muscles that use fatty acids as a dietary fuel have high concentrations of carnitine.

There are three different forms of carnitine:

  • L-carnitine
  • acetyl-L-carnitine
  • propionyl-L-carnitine

The liver and kidney usually produce enough carnitine in the human body, so topping up with food or supplements is not necessary. There is no recommended daily intake.

However, genetic or medical reasons can cause some people produce too little.

Primary systemic carnitine deficiency can happen when the protein that is responsible for bringing carnitine into cells undergoes a genetic change. This deficiency causes problems with processing food.

This rare condition can lead to:

  • low plasma carnitine
  • progressive cardiomyopathy, or heart muscle disease
  • skeletal myopathy
  • hypoglycemia
  • hypoammonemia
  • weak muscles in the hips, shoulders upper arms, legs, neck, and jaw muscles

Untreated it is fatal. The symptoms gradually worsen from infancy to early adulthood.

To treat it, the physician will prescribe pharmacological doses of carnitine, to correct the problems of cardiomyopathy and muscle weakness.

If it happens as a result of other metabolic diseases, this is secondary carnitine deficiency. Cancer and aging reduce carnitine levels.

People who lack carnitine may need to take supplements or eat specially enriched foods.

Foods that provide carnitine are mainly animal products, dairy, poultry, and meat. Red meat has one of the highest concentrations.

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Red meat is a good source of carnitine.

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 ounces contains 3 to 5 mg
  • Cheese, cheddar, 2 ounces contains 2mg

Non-animal sources include whole-wheat bread and asparagus.

Adults whose diets are rich in red meat consume on average around 60 to 180mg of carnitine per day. A vegan diet normally provides between 10 and 12mg per day.

Studies suggest that the body absorbs 54 to 86 per cent of dietary carnitine into the bloodstream, but only 14 to 18 percent when it is taken as a supplement.

Carnitine is said to have many therapeutic properties that may be useful in treating a range of conditions and illnesses.

As an antioxidant, carnitine fights off harmful free radicals, which cause severe damage to cells.

Health conditions that carnitine may be used to treat include heart failure or heart attack, angina, and diabetic neuropathy.

One review study has stated that acetyl-L-carnitine (ALC) had a moderate effect on reducing pain, but the evidence is still conflicting, and more research is needed.

One study found that ALC is as effective as a conventional treatment, methylcobalamin (MC), in treating diabetic peripheral neuropathy.

Another investigation, involving 19 patients, found that ALC did not change the frequency or severity of the condition.

Angina and heart problems

For some time, studies have suggested that carnitine may help treat the symptoms of angina if used alongside conventional treatment. The findings were published in Drugs Under Experimental and Clinical Research.

In 2013, a review and meta-analysis linked L-carnitine with a 27 percent reduction in all-cause mortality, and notably, a 65 percent drop in ventricular arrhythmias and a 40 percent fall in the development of angina. However, it did not lead to a fall in the development of heart failure or a repeat myocardial infarction (MI).

Carnitine may also normalize the type of blood vessel dysfunction that happens with congenital heart defects, according to Dr. Stephen M. Black, cell and molecular physiologist at the Vascular Biology Center at the Medical College of Georgia at Georgia Regents University.

Fatigue and other symptoms of chronic disease

Most chronic diseases lead to a loss of mitochondrial function that can result in fatigue and other symptoms.

Research published in Alternative Therapies In Health And Medicine suggests that combinations of supplements, including carnitine, might help improve mitochondrial function.

The researchers concluded:

"Combinations of these supplements can reduce significantly the fatigue and other symptoms associated with chronic disease and can naturally restore mitochondrial function, even in long-term patients with intractable fatigue."

They believe carnitine may reduce symptoms of fatigue in patients with chronic diseases.

Intermittent claudication

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 lead to pain when walking or running, because damage or narrowing of an artery leads to poor blood supply.

It tends to affect the blood vessels in the legs, but it can affect the arms too.

The pain usually occurs in the feet, calves, thighs, hips or buttocks, depending on where the artery damage or narrowing occurs.

The authors found that patients with peripheral arterial disease were able to walk comfortably for longer times and distances after using PLC.

Alzheimer's disease

A study published in the journal Neurobiology of Aging concluded that acetyl-L-carnitine may help people with Alzheimer's disease.

Those who took the supplement saw a smaller drop in their Mini-Mental Status and Alzheimer's Disease Assessment Scale test scores, compared with those on placebo.

Sexual dysfunction

PLC and ALC improved the effectiveness of sildenafil, or Viagra, in restoring sexual potency.

Studies on men with infertility have suggested that 2 to 3 grams a day for 3 to 4 months can increase sperm quality, and that 2 grams for 2 months may increase sperm motility. However, other studies have not confirmed this.

HIV or AIDS

Carnitine supplements may help reverse the drop critical immune cells in people with HIV or AIDS. A reduction in carnitine levels may occur as a result of the treatment for these conditions, but more studies are needed to confirm the results.

The University of Maryland Medical Center (UMM) note that people sometimes take carnitine for weight loss, Peyronie disease, kidney disease, and hyperthyroidism, which is an overactive thyroid.

They point out that there is not enough scientific evidence to support any of these uses.

Treating a serious condition with supplement can sometimes be hazardous. Anyone with symptoms or a diagnosis of a serious disease people should seek conventional treatment from a qualified medical professional.

Many athletes and gym enthusiasts use carnitine, and it is available over the counter as a sports or health supplement.

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Carnitine is often used to support exercise and weight loss.

The hypothesis is that carnitine supplementation improves exercise performance in healthy athletes through various mechanisms.

Advocates claim that it:

  • alters glucose homeostasis
  • enhances acylcarnitine production
  • modifies the way the body responds to training
  • alters muscle fatigue resistance
  • improved exercise tolerance
  • increased respiratory muscle strength

A rordent study, published in 2016, suggested that carnitine may reduce oxidative stress during exercise.

Researchers who gave L-carnitine to older patients with chronic obstructive pulmonary disease (COPD) alongside exercise testing found that exercise capacity improved in the eight men who completed the experiment.

L-carnitine, they concluded, "appeared to be safe, well-tolerated and positively influenced exercise capacity and respiratory muscle strength in COPD patients."

The National Institutes of Health (NIH) note that among athletes taking between 2 and 6 milligrams a day for a range of 1 to 28 days, there was "no consistent evidence" of any benefits.

According to the NIH, "Supplements do not appear to increase the body's use of oxygen or improve metabolic status when exercising, nor do they necessarily increase the amount of carnitine in muscle."

Although the NIH says that, as a therapy, carnitine is "generally safe and well tolerated," carnitine supplements can lead to some unwanted effects.

According to the National Institutes of Health (NIH), an intake of 3 grams of carnitine a day leads to:

Other sources suggest that an increase in appetite may occur, and a rash.

Rarer 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:

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 recommend that anyone who does decide to take carnitine supplements should consider acetyl-L-carnitine at 500 mg to 1,000 mg a day.

Before taking any supplements, it is always advisable to speak to a doctor.