Carnitine is a nutrient that helps the body turn fat into energy. It is produced by the body in the liver and kidneys and stored in the skeletal muscles, heart, brain, and sperm.

Usually, the body can make all the carnitine it needs. Some people, however, may be deficient in carnitine because their bodies cannot make enough carnitine or transport it into tissues so it can be used. Some other conditions, such as angina or intermittent claudication, can also cause insufficient carnitine in the body, as can some medications.

Carnitine has been proposed as a treatment for many conditions because it helps reduce oxidative stress. Some of the conditions carnitine may help treat are serious, and in those cases, you should take the supplement under the supervision of your doctor, as an adjunct therapy to conventional medicine. For other conditions, such as fatigue or improving exercise performance, carnitine appears safe but seems to have little effect.

Heart Conditions

• Angina -- The best evidence for carnitine's use for heart disease is as an addition to conventional treatment for stable angina. Several clinical trials indicate that L-carnitine and propionyl-L-carnitine can help reduce symptoms of angina and improve the ability of those with angina to exercise without chest pain. You should not self-treat chest pain with carnitine, however. See your doctor for diagnosis and conventional treatment, and take carnitine only under your doctor's supervision.
• Heart attack -- There is little evidence for using carnitine after a heart attack due to a lack of well-designed studies. Some small studies suggest that people who take L-carnitine supplements soon after 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 heart failure. However, other studies have shown no benefit. Treatment with oral carnitine may also improve muscle weakness. Carnitine should be used along with conventional medication under your doctor's supervision.
• Heart Failure -- A few small studies have suggested that carnitine (usually propionyl-L-carnitine) can help reduce symptoms of heart failure and improve exercise capacity in people with heart failure. However, more and larger studies are needed to confirm any benefit.

Peripheral Vascular Disease

Decreased blood flow to the legs from atherosclerosis (plaque build up) often causes an aching or cramping pain in the legs while walking or exercising. This pain is called intermittent claudication, and the diminished blood flow to the legs is called peripheral vascular disease (PVD). A number of studies show that carnitine can help reduce symptoms and increase the distance that people with intermittent claudication can walk. Most studies have used propionyl-L-carnitine. Scientists don't know whether L-carnitine would have the same effect.

Diabetic Neuropathy

When high blood sugar levels damage nerves in the body, especially the arms, legs, and feet, the condition is called diabetic neuropathy. Some small preliminary studies suggest acetyl-L-carnitine may help reduce pain and increase normal feeling in affected nerves. It is also possible that carnitine can help nerves regenerate. More research is needed.

Exercise Performance

Although carnitine is often taken to improve exercise performance, there is no evidence it works.

Weight Loss

Although L-carnitine has been marketed as a weight loss supplement, there is no scientific evidence to show that it improves weight loss, however some studies show that oral carnitine reduces fat mass, increases muscle mass, and reduces fatigue. All of these effects may contribute to weight loss.

Alzheimer's Disease and Memory Impairment

The evidence is mixed as to whether carnitine is useful in treating Alzheimer's disease. Several early studies showed that acetyl-L- carnitine, might help delay the progression of Alzheimer's disease, relieve depression related to senility and other forms of dementia, and improve memory in the elderly. Unfortunately, larger and better-designed studies found no benefit. You should take carnitine for Alzheimer's and other forms of dementia only under the supervision of your doctor.

Kidney Disease and Dialysis

Because the kidneys produce carnitine, kidney disease could lead to a deficiency of carnitine in the body. If you have kidney disease, your doctor may prescribe carnitine; however, do not take it without medical supervision.

Male Infertility

Low sperm counts have been linked to low carnitine levels in men. Several studies suggest that L-carnitine supplementation may increase sperm count and mobility.

Erectile Dysfunction

Preliminary studies suggest propionyl-L-carnitine may help improve male sexual function. One study found that carnitine significantly improved the effectiveness of sidenafil (Viagra) in men with diabetes who had not previously responded to Viagra. More studies are needed.

Chronic Fatigue Syndrome (CFS)

Some researchers speculate that CFS may be caused by deficiencies in a variety of nutrients, including carnitine. L-carnitine has been compared to a medication for fatigue in a study of 30 people with CFS. Those who took L-carnitine did much better than those who took the medication, particularly after receiving the supplement for 4 - 8 weeks. However, the study was not well-designed, and many of those who took the prescription medication dropped out of the study. More research is needed to determine whether carnitine has any true benefit for CFS.

Peyronie's Disease

Peyronie's disease is characterized by a curvature of the penis that leads to pain during an erection because of blocked blood flow. One promising study compared acetyl-L-carnitine to tamoxifen in 48 men with this condition. Acetyl-L-carnitine worked better than the medication at reducing pain during intercourse and minimizing the curve of the penis. Acetyl-L-carnitine also had fewer side effects than tamoxifen. Although the study results are encouraging, more research is needed.

Hyperthyroidism

Some research suggests that L-carnitine may prove useful for preventing or reducing symptoms of an overactive thyroid, such as insomnia, nervousness, elevated heart rate, and tremors. In fact, in one study, a small group of people with hyperthyroidism had improvement in these symptoms, as well as normalization of their body temperature, when taking carnitine. But a larger, well-designed clinical trial is needed before carnitine can be recommended for hyperthyroidism.

Red meat (particularly lamb) and dairy products are the primary sources of carnitine. It can also be found in fish, poultry, tempeh, wheat, asparagus, avocados, and peanut butter.

Carnitine is available as a supplement in a variety of forms.

• L-carnitine: the most widely available and least expensive
• Acetyl-L-carnitine: Often used in studies for Alzheimer's disease and other brain disorders
• Propionyl-L-carnitine: Often used in studies for heart disease and peripheral vascular disease

Avoid D-carnitine supplements. They interfere with the natural form of L-carnitine and may produce undesirable side effects.

In some cases, L-carnitine may be taken by prescription or given intravenously by a doctor.

Pediatric

Carnitine supplements should only be given to children under a doctor's supervision, after determining that a carnitine deficiency exists.

Adult

Recommended doses of L-carnitine vary depending on the health condition being treated. The usual dose is between 1 - 3 g per day:

• Angina and heart failure: 1.5 - 2 g per day
• Heart disease: 600 - 1,200 mg 3 times daily, or 750 mg 2 times daily
• Peripheral vascular disease: 2 - 4 g per day
• Diabetic neuropathy: 3 g per day
• Male infertility: 300 - 1,000 mg 3 times daily
• Chronic fatigue syndrome: 500 - 1,000 mg 3 - 4 times per day
• Overactive thyroid: 2 - 4 g per day in 2 - 4 divided doses

Because supplements may have side effects or interact with medications, you should take them only under the supervision of a knowledgeable health care provider.

Side effects are generally mild. High doses (5 or more grams per day) may cause diarrhea. Other rare side effects include increased appetite, body odor, and rash.

People with the following conditions should talk to their doctor before taking carnitine:

• Peripheral vascular disease
• Hypertension (high blood pressure)
• Alcohol-induced liver disease (cirrhosis)
• Diabetes
• Kidney disease

If you are currently being treated with any of the following medications, you should not use carnitine without first talking to your health care provider.

AZT -- In a laboratory study, L-carnitine supplements protected muscle tissue against toxic side effects from AZT, a medication used to treat HIV and AIDS. More studies are needed to confirm whether L-carnitine would also have this effect in people.

Doxorubicin -- Treatment with L-carnitine may protect heart cells against the toxic side effects of doxorubicin, a chemotherapy medication used to treat cancer, without reducing the effectiveness of medication. Always talk to your oncologist before combining any complementary or alternative therapy with chemotherapy.

Isotretinoin -- Isotretinoin (Accutane), a strong medication used for severe acne, can cause abnormalities in liver function, measured by a blood test, as well as high cholesterol and muscle pain and weakness. These symptoms are similar to those seen with carnitine deficiency. Researchers in Greece showed that a large group of people who had side effects from isotretinoin got better when taking L-carnitine compared to those who took a placebo.

Valproic acid -- The anticonvulsant medication valproic acid may lower blood levels of carnitine and can cause carnitine deficiency. Taking L-carnitine supplements may prevent any deficiency and may also reduce the side effects of valproic acid.

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