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Unless you suffer from certain medical problems, your kidneys and liver make enough carnitine from the amino acids methionine and lysine to meet your body's needs. Thus, there isn't a recommended dietary allowance for carnitine, and it isn't considered an essential nutrient 1. Check with your doctor before taking supplements containing L-carnitine or other forms of carnitine to make sure it's safe for you -- and to figure out a correct dosage 1.
If you are experiencing serious medical symptoms, seek emergency treatment immediately.
According to a review article published in Mayo Clinic Proceedings in June 2013, L-carnitine may help prevent heart disease 5.
Where It's Found
L-carnitine is the least expensive and most commonly available carnitine supplement, but acetyl-L-carnitine is the form often used in studies on brain disorders and aging, and propionyl-L-carnitine is used in heart disease studies. Avoid D-carnitine supplements, as they may interfere with L-carnitine absorption 1.
A study published in Nature Medicine in 2013 found that the metabolism of L-carnitine may increase the risk for heart disease by promoting atherosclerosis, or clogging of the arteries, in some people 4. This effect appears to be more common in meat-eaters than in vegetarians, but further research is necessary to clarify the effects of L-carnitine on heart disease risk.
Side Effects and Contraindications
High doses of L-carnitine may cause:
- stomach cramps
- body odor
- an increased appetite
L-carnitine may interact with certain medications, including thyroid hormones, making them potentially less effective. L-carnitine supplements may increase the frequency of seizures in those with seizure disorders 1.
L-carnitine may interact with certain medications, including thyroid hormones, making them potentially less effective. This effect appears to be more common in meat-eaters than in vegetarians, but further research is necessary to clarify the effects of L-carnitine on heart disease risk. Avoid D-carnitine supplements, as they may interfere with L-carnitine absorption.
- Office of Dietary Supplements: Carnitine
- Linus Pauling Institute: L-Carnitine
- University of Maryland Medical Center: Carnitine (L-Carnitine)
- Nature Medicine: Intestinal Microbiota Metabolism of L-Carnitine, a Nutrient in Red Meat, Promotes Atherosclerosis
- Mayo Clinic Proceedings: L-Carnitine in the Secondary Prevention of Cardiovascular Disease: Systematic Review and Meta-Analysis
- Eising/Photodisc/Getty Images