Carnitine is a substance found in the cells of your body, mostly in the skeletal muscles and heart muscles. It's necessary for energy production because it transports long-chain fatty acids into the mitochondria (powerhouses of the cells) to be burned for energy, then it helps remove toxic wastes, so they don't build up in the mitochondria.
Carnitine is found in some of the foods you eat. Animal foods contain the most carnitine, especially beef and lamb. Milk, fish, and chicken are all good sources, as well. Plant sources include wheat, asparagus, tempeh (a soy product), avocados, and peanut butter. A typical diet provides 60 to 180 milligrams of carnitine each day, although vegans get about 10 to 12 milligrams. Your body can conserve carnitine if you need it, but usually excess carnitine is removed by the kidneys.
You don't need to worry about getting carnitine from your diet, even if you rarely eat meat, because your body normally makes carnitine in your liver and kidneys. Deficiency can occur, either from a genetic disorder that reduces the body's ability to make or transport carnitine, as a side effect of certain medication, or as the result of certain heart conditions.
Carnitine is commercially available as a dietary supplement. Common forms include L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine. Don't use any D- forms because they can interact with your natural carnitine stores.
Because it's important for energy production, carnitine supplements are often taken by athletes to boost physical performance or used as a weight loss aid. They're also touted as anti-aging supplements and as a way to improve memory. However, scientific evidence doesn't indicate any benefit of carnitine supplementation in these situations. Carnitine supplements are best suited to treat carnitine deficiency.
Research does support the potential for carnitine as treatment for claudication, which is a condition where the leg muscles don't get enough oxygen due to lack of blood flow. It may also help reduce the risk of heart failure in people who've already had heart attacks. Supplementation may increase sperm count in men who have low carnitine levels, and might also reduce some of the symptoms of hyperthyroid (overactive thyroid) disease.
Small studies also suggest carnitine may be beneficial for certain nerve problems, including diabetic neuropathy. More research is needed in these areas and using carnitine supplements for these situations requires medical supervision, so speak to your health care provider before taking them.
Carnitine supplements can have unwanted side effects. They can cause nausea, increased appetite, a fish-like body odor, and rashes when taken in large doses (more than five grams per day). They can also interact with certain medications.
National Institutes of Health, Office of Dietary Supplements. "Dietary Supplement Fact Sheet: Carnitine." Accessed May 12, 2012. http://ods.od.nih.gov/factsheets/Carnitine-HealthProfessional/.
Natural Standard Research Collaboration. "L-Carnitine, Natural Standard Professional Monograph." http://naturalstandard.com.
University of Maryland Medical Center. "Carnitine (L-Carnitine)." Accessed May 12, 2012. http://www.umm.edu/altmed/articles/carnitine-l-000291.htm.