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Carnitine (L-carnitine)

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L-carnitine is a derivative of the amino acid, lysine. Its name is derived from the fact that it was first isolated from meat (carnus) in 1905. Only the L-isomer of carnitine (Figure 1) is biologically active. Carnitine is a substance that helps the body turn fat into energy. Your body makes it and stores it in the skeletal muscles, heart, brain, and sperm.
Usually, your body can make all the carnitine it needs. Some people, however, may not have enough carnitine because their bodies cannot make enough or can’t transport it into tissues so it can be used.
Some of the conditions carnitine may help treat are:
1- Heart Conditions
• Angina -- Some good evidence shows that carnitine can be used along with conventional treatment for stable angina. Several clinical trials show that L-carnitine can help reduce symptoms of angina and improve the ability of people with angina to exercise without chest pain. Do not self-treat chest pain with carnitine, however. See your health care provider for diagnosis and conventional treatment, and take carnitine only under your health care provider's supervision.
• Heart attack -- A few studies have found that carnitine may help when used with conventional medicines after a heart attack, but not all studies agree. Some small studies suggest that people who take L-carnitine supplements soon after a heart attack may be less likely to have another heart attack, die of heart disease, have 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 health care provider supervision.
• Heart failure -- A few small studies have suggested that 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 know for sure.
2- Peripheral Vascular Disease
Decreased blood flow to the legs (called Peripheral Vascular Disease or PVD) from atherosclerosis or hardening of the arteries -- where plaque builds up in the arteries -- often causes an aching or cramping pain in the legs while walking or exercising (called intermittent claudication). Several studies show that carnitine can help reduce symptoms and increase the distance that people with intermittent claudication can walk.
3- Diabetic Neuropathy
Diabetic neuropathy happens when high blood sugar levels damage nerves in the body, especially the arms, legs, and feet, causing pain and numbness. Some small preliminary studies suggest acetyl-L-carnitine may help reduce pain and increase feeling in affected nerves. It is also possible that carnitine can help nerves regenerate. More research is needed.
4- Exercise Performance
Although carnitine is often taken to boost exercise performance, more research is needed
5- Weight Loss
Some studies do show that oral carnitine reduces fat mass, increases muscle mass, and reduces fatigue, which may contribute to weight loss in some people.
6- Alzheimer's Disease and Memory Impairment
Several early studies showed that acetyl-L-carnitine, might help slow down the progression of Alzheimer's disease, relieve depression related to senility and other forms of dementia, and improve memory in the elderly. People should take carnitine for Alzheimer's and other forms of dementia only under the supervision of their health care provider.
7- Kidney Disease and Dialysis
Because the kidneys make carnitine, kidney disease could lead to low levels of carnitine in the body. If you have kidney disease, your health care provider may prescribe carnitine -- but you shouldn’t take it without medical supervision.
8- Male Infertility
Low sperm counts have been linked to low carnitine levels in men. Several studies suggest that L-carnitine supplements may increase sperm count and mobility.
9- Erectile Dysfunction
Preliminary studies suggest propionyl-L-carnitine may help improve male sexual function. One study found that carnitine improved the effectiveness of sidenafil (Viagra) in men with diabetes who had not previously responded to Viagra. In another study, a combination of propionyl-L-carnitine and acetyl-L-carnitine improved the effectiveness of Viagra in men who had erectile dysfunction after prostate surgery. More studies are needed.
10- Hyperthyroidism
Some research suggests that L-carnitine may help prevent or reduce symptoms of an overactive thyroid, such as insomnia, nervousness, heart palpitations, and tremors. A larger, better-designed clinical trial is needed.
Dietary Sources
Red meat (particularly lamb) and dairy products are the main food sources of carnitine. It can also be found in fish, poultry, wheat, asparagus, avocados, and peanut butter.
Available Forms
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 unwanted side effects.
How to Take It
Pediatric
Don’t give carnitine supplements to a child without your child's health care provider's supervision.
Adult
Recommended doses of L-carnitine vary depending on the health condition being treated. The usual dose is between 1 - 3 g per day.
Precautions
You should take L - carnitine 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.
Possible Interactions
Zidovudine -- In a laboratory study, L-carnitine supplements protected muscle tissue against toxic side effects from Zidovudine, a medication used to treat HIV and AIDS. More studies are needed to know whether L-carnitine would have the same 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 making the medication any less effective. Always talk to your oncologist before using any complementary or alternative therapy with chemotherapy.
Isotretinoin (Accutane) -- Accutane, a strong medication used for severe acne, can cause liver problems, as well as high cholesterol and muscle pain and weakness. These symptoms are like those seen with carnitine deficiency. Researchers in Greece showed that a large group of people who had side effects from Accutane got better when taking L-carnitine compared to those who took a placebo.
Thyroid hormone -- Carnitine may stop thyroid hormone from getting into cells, and theoretically may make thyroid hormone replacement less effective. If you take thyroid replacement hormone, talk to your health care provider before taking carnitine.
Valproic acid (Depakote) -- The anti-seizure medication valproic acid may lower blood levels of carnitine. Taking L-carnitine supplements may reduce the side effects of valproic acid. However, taking carnitine may increase the risk of seizures in people with a history of seizures.
Supporting Research
Benvenga S, Ruggieri RM, Russo A, Lapa D, Campenni A, Trimarchi F. Usefulness of L-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: a randomized, double-blind placebo-controlled clinical trial. J Clin Endocrinol Metab. 2001;86(8):3579-3594.
Berni A, Meschini R, Filippi S, Palitti F, De Amicis A, Chessa L. L-carnitine enhances resistance to oxidative stress by reducing DNA damage in Ataxia telangiectasia cells. Mutat Res. 2008;650(2):165-74.
Biagiotti G, Cavallini G. Acetyl-L-carnitine vs tamoxifen in the oral therapy of Peyronie's disease: a preliminary report. BJU Int. 2001;88(1):63-67.
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Cavallini G, Modenini F, Vitali G, et al. Acetyl-L-carnitine plus propionyl-L-carnitine improve efficacy of sildenafil in treatment of erectile dysfunction after bilateral nerve-sparing radical retropubic prostatectomy. Urology. 2005;66:1080-1085.
Cruciani RA, Dvorkin E, Homel P, Malamud S, Culliney B, Lapin J, Portenoy RK, Esteban-Cruciani N. Safety, tolerability and symptom outcomes associated with L-carnitine supplementation in patients with cancer, fatigue, and carnitine deficiency: a phase I/II study. J Pain Symptom Manage. 2006 Dec;32(6):551-9.
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Lynch KE, Feldman HI, Berlin JA, Flory J, Rowan CG, Brunelli SM. Effects of L-carnitine on dialysis-related hypotension and muscle cramps: a meta-analysis. Am J Kidney Dis. 2008;52(5):962-71.
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Rathod R, Baig MS, Khandelwal PN, Kulkarni SG, Gade PR, Siddiqui S. Results of a single blind, randomized, placebo-controlled clinical trial to study the effect of intravenous L-carnitine supplementation on health-related quality of life in Indian patients on maintenance hemodialysis. Indian J Med Sci. 2006 Apr;60(4):143-53.
Sinclair S. Male infertility: nutritional and environmental considerations. Alt Med Rev. 2000;5(1):28-38.
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Xue YZ, Wang LX, Liu HZ, Qi XW, Wang XH, Ren HZ. L-carnitine as an adjunct therapy to percutaneous coronary intervention for non-ST elevation myocardial infarction. Cardiovasc Drugs Ther. 2007;21(6):445-8.