Carnitine is an amino acid the body uses to turn fat into energy. It is not normally considered an essential nutrient because the body can manufacture all it needs. However, supplemental carnitine may improve the ability of certain tissues to produce energy. This effect has led to the use of carnitine in various muscle diseases as well as heart conditions.

Sources

There is no dietary requirement for carnitine. However, a few individuals have a genetic defect that hinders the body's ability to make carnitine. In addition, diseases of the liver, kidneys, or brain may inhibit carnitine production. Certain medications, especially the antiseizure drugs valproic acid (Depakene) and phenytoin (Dilantin), may reduce carnitine levels; however, whether taking extra carnitine would be helpful has not been determined.^1-11 Heart muscle tissue, because of its high energy requirements, is particularly vulnerable to carnitine deficiency.

The principal dietary sources of carnitine are meat and dairy products, but to obtain therapeutic dosages a supplement is necessary.

Therapeutic Dosages

Typical dosages for the diseases described here range from 500 to 1,000 mg 3 times daily. Carnitine is taken in three forms: L-carnitine (for heart and other conditions), propionyl-L-carnitine (for heart conditions), and acetyl-L-carnitine (for Alzheimer's disease). The dosage is the same for all three forms.

Therapeutic Uses

Carnitine is primarily used for heart-related conditions. Some evidence suggests that it can be used along with conventional treatment for angina, to improve symptoms and reduce medication needs.^12-17 When combined with conventional therapy, it may also reduce mortality rates after a heart attack.^18,19

Lesser evidence suggests that it may be helpful for a condition called intermittent claudication (pain in the legs after walking due to narrowing of the arteries),^20-30 as well as congestive heart failure.^31-34 In addition, a few studies suggest that carnitine may be useful for cardiomyopathy.^35,36

Carnitine may also be helpful for improving exercise tolerance in people with chronic pulmonary obstruction disease (COPD), more commonly known as emphysema.^37,38,39

Warning: You should not attempt to self-treat any of these serious medical conditions, nor should you use carnitine as a substitute for standard drugs.

One study found evidence that acetyl-L-carnitine is helpful for Peyronie's disease, a condition affecting the penis.¹¹⁸

Some studies have found evidence that one particular form of carnitine, acetyl-L-carnitine, might be helpful in Alzheimer's disease,^40-46 but the two most recent and largest studies found no benefit.^47,48 This form of carnitine has also been investigated for treatment of depression in the elderly.^49,50

A genetic condition called fragile X syndrome can cause behavioral disturbances such as hyperactivity, along with mental retardation, autism, and alterations in appearance. A preliminary study of 17 boys found that acetyl-L-carnitine might help to reduce hyperactive behavior associated with this condition.⁵¹

Additionally, a preliminary study suggests that carnitine may be useful for improving blood sugar control in individuals with type 2 (adult-onset) diabetes.⁵² It also might help prevent diabetic cardiac autonomic neuropathy (injury to the nerves of the heart caused by diabetes).⁵³ Weak evidence suggests that carnitine may be able to improve cholesterol and triglyceride levels,⁵⁴ and also help individuals with degeneration of the cerebellum (the structure of the brain responsible for voluntary muscular movement).⁵⁵ One very small study suggests carnitine may be helpful for reducing symptoms of chronic fatigue syndrome.⁵⁶ One study suggests that carnitine may be of value for treating hyperthyroidism.⁵⁷

Uncontrolled studies suggest that L-carnitine or acetyl-L-carnitine may be helpful for improving sperm function.^58-66

Weak evidence also suggests that carnitine may be helpful for decreasing the toxicity of AZT (a drug used to treat AIDS). ^67,68

Carnitine is widely touted as a physical performance enhancer, but there is no real evidence that it is effective and some research indicates that it does not work.⁶⁹Little to no evidence supports other claimed benefits such as treating irregular heartbeat, Down'ssyndrome, muscular dystrophy, and alcoholic fatty liver disease.

What Is the Scientific Evidence for Carnitine?

Angina

Carnitine might be a good addition to standard therapy for angina. In one controlled study, 200 individuals with angina (the exercise-induced variety) took either 2 g daily of L-carnitine or were left untreated. All the study participants continued to take their usual medication for angina. Those taking carnitine showed improvement in several measures of heart function, including a significantly greater ability to exercise without chest pain.⁷⁰ They were also able to reduce the dosage of some of their heart medications (under medical supervision) as their symptoms decreased.

Unfortunately, the results of this study can't be fully trusted, because researchers didn't use a double-blind protocol. Another trial that did use a double-blind, placebo-controlled design tested L-carnitine in 52 individuals with angina, and found evidence of benefit.⁷¹

In addition, several small studies (some of them double-blind) tested propionyl-L-carnitine for the treatment of angina, and also found evidence of benefit.^72-75

Intermittent Claudication

People with advanced hardening of the arteries, or atherosclerosis, often have difficulty walking due to lack of blood flow to the legs. Pain may develop after walking less than half a block. Although carnitine does not increase blood flow, it appears to improve the muscle's ability to function under difficult circumstances.⁷⁶ A 12-month double-blind placebo-controlled trial of 485 patients with intermittent claudication evaluated the potential benefits of propionyl-L-carnitine.⁷⁷ Participants with relatively severe disease showed a 44% improvement in walking distance as compared to placebo. However, no improvement was seen in those with mild disease. Another double-blind study followed 245 people and also found benefit.⁷⁸

Similar results have been seen in most but not all other studies of L-carnitine or propionyl-L-carnitine.^79-87 Propionyl-L-carnitine may be more effective for intermittent claudication than plain carnitine.

Congestive Heart Failure

Several small studies have found that carnitine, often in the form of propionyl-L-carnitine, can improve symptoms of congestive heart failure.^88-91In one trial, benefits were maintained for 60 days after treatment with carnitine was stopped.⁹²

After a Heart Attack

Carnitine may help reduce death rate after a heart attack. In a 12-month placebo-controlled study, 160 individuals who had experienced a heart attackreceived 4 g of L-carnitine daily or placebo, in addition to other conventional medication. The mortality rate in the treated group was significantly lower than in the placebo group, 1.2% versus 12.5%, respectively. There were also improvements in heart rate, blood pressure, angina (chest pain), and blood lipids.⁹³ A larger double-blind study of 472 people found that carnitine may improve the chances of survival if given within 24 hours after a heart attack.⁹⁴

Note: Carnitine is used along with conventional treatment, not as a substitute for it.

Chronic Obstructive Pulmonary Disease (COPD)

Evidence from three double-blind placebo-controlled studies enrolling a total of 49 individuals suggests that L-carnitine can improve exercise tolerance in COPD, presumably by improving muscular efficiency in the lungs and other muscles.^95,96,97

Alzheimer's Disease

Numerous double- or single-blind studies involving a total of more than 1,400 people have evaluated the potential benefits of acetyl-L-carnitine in the treatment of Alzheimer's disease and other forms of dementia.^98-109 Early studies found some evidence of benefit, although it was generally quite modest. However, the two most recent and best-designed studies found no benefit.

A double-blind placebo-controlled trial that enrolled 431 participants for 1 year found no significant improvement at all in the group treated with acetyl-L-carnitine.¹¹⁰ A close look at the results appeared to suggest some benefit in individuals who developed Alzheimer's disease at a particularly young age. However, when this possibility was tested in a 1-year double-blind placebo-controlled trial of 229 patients with early-onset Alzheimer's, no benefits were seen.¹¹¹

Mild Depression

A double-blind study of 60 seniors with mild depression found that treatment with 3 g of carnitine daily over a 2-month period significantly improved symptoms as compared to placebo.¹¹² Positive results were seen in another study as well.¹¹³

Hyperthyroidism

Enlargement of the thyroid (goiter) can be due to many causes, including cancer and iodine deficiency. In some cases, thyroid enlargement occurs without any known cause, so-called benign goiter.

Treatment of benign goiter generally consists of taking thyroid hormone pills. This causes the thyroid gland to become less active, and the goiter shrinks. However, there may be undesirable effects as well. Symptoms of hyperthyroidism (too much thyroid hormone) can develop, including heart palpitations, nervousness, weight loss, and bone breakdown.

A double-blind, placebo-controlled trial found evidence that use of L-carnitine could alleviate many of these symptoms. This 6-month study evaluated the effects of L-carnitine in 50 women who were taking thyroid hormone for benign goiter.¹¹⁴ The results showed that a dose of 2 or 4 g of carnitine daily protected participants' bones and reduced other symptoms of hyperthyroidism.

Carnitine is thought to affect thyroid hormone by blocking its action in cells.¹¹⁵ This suggests a potential concern: Carnitine might be harmful for people who have low or borderline thyroid levels to begin with. This possibility has not been well explored as yet.

Peyronie's Disease

Peyronie's disease is an inflammatory condition of the penis that develops in stages. In the first stage, penile pain occurs with erection; next, the penis becomes curved; finally, erectile dysfunction may occur. Many medications have been tried for Peyronie's disease, with some success. One such drug is tamoxifen (better known as a treatment to prevent breast cancer recurrence.) A 3- month, double-blind study compared the effectiveness of acetyl-L-carnitine (1 gram twice daily) against tamoxifen; the study enrolled 15 men in the first stage of Peyronie's disease and 33 men in the second stage.¹¹⁸ The result indicated that acetyl-L-carnitine reduced penile curvature while tamoxifen did not; the supplement also reduced pain and slowed disease progression to a greater extent than the drug. Furthermore, while the drug caused various side effectsa and the supplement caused none.