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What is carnitine?

L-carnitine is an amino acid derivative, a conditionally essential nutrient produced in your body from the amino acids lysine and methionine, but in certain conditions you may need to get additional amounts from foods in order to be healthy [2]. Healthy people, including strict vegetarians (vegans) do not need carnitine from foods or supplements [1,2].

Name origin: from the Latin carnus = flesh, since carnitine was first isolated from meat [1].

Two structural forms (L- and D-) exist, but only L-carnitine is biologically active.

Carnitine Functions in the Human Body

L-carnitine helps the heart and skeletal muscles to efficiently use fats (especially long-chain fatty acids) and glucose as a fuel [2].

Foods Rich in Carnitine

  • ANIMAL FOODS: meat, fish and dairy products [2]
  • PLANT FOODS: avocado, asparagus
  • Human breast milk also contains carnitine.
  • Non-milk baby formulas are fortified with carnitine.

Carnitine Deficiency: Causes, Symptoms

Causes [2]:

  • Chronic kidney failure
  • Vitamin C deficiency
  • Medications: anticonvulsants (valproic acid), drugs used in AIDS (zidovudine [AZT)] didanosine [ddI], zalcitabine [ddC] and stavudine [d4T]), antibiotics (pivampicillin, pivmecillinam, pivcephalexin,) chemotherapeutics (ifosfamide, cisplatin)
  • Rare, genetic forms of L-carnitine deficiency:
    • In primary systemic L-carnitine deficiency there is decreased absorption and increased excretion of L-carnitine. Disease presents in early childhood with a progressive heart disorder (cardiomyopathy) and skeletal muscles weakness and pain (myopathy), low blood levels of L-carnitine, glucose (hypoglycemia) and ammonia (hypoammonemia). Treatment is by L-carnitine.
    • Myopathic carnitine deficiency is less severe form in which the main symptoms are muscle pain and weakness beginning in childhood or adolescence. Blood L-carnitine levels are normal.

L-carnitine deficiency due to a low dietary carnitine intake in healthy people is not known, not even in strict vegetarians or preterm newborns [2].

L-Carnitine Supplements

  • Nonprescription (over-the-counter) oral carnitine supplements:
    • L-carnitine and N-acetyl-L-carnitine (the only forms available in the U.S.)
    • Andpropyonil-L-carnitine (available in Europe)
    • L-carnitine tartrate
    • L-carnitine fumarate
  • By prescription
    • Oral L-carnitine
    • L-carnitine as an intravenous injection

Carnitine Health Benefits

Carnitine supplements are EFFECTIVE in the

  • Treatment of carnitine deficiency [2].

Carnitine supplements are POSSIBLY EFFECTIVE in [1,2]:

  • Improving symptoms of a kidney failure requiring hemodialysis (by using intravenous L-carnitine) [8]
  • Increasing walking distance in patients with severe atherosclerosis of leg arteries with leg pain during walking (intermittent claudication) [6,10]
  • Reducing nerve pain (by using oral acetyl-L-carnitine ) [7]

L-carnitine is LIKELY INEFFECTIVE in increasing exercise performance [4].

There is INSUFFICIENT EVIDENCE [2,4] about the effectiveness of carnitine supplements in the prevention or treatment of Alzheimer disease, anorexia, attention deficit-hyperactivity disorder (ADHD), autism, beta-thalassemia, cachexia (weigh loss in cancer), chest pain in a heart disease (angina pectoris), chronic fatigue syndrome, chronic obstructive pulmonary disease (COPD), clogged arteries, coronary artery disease, diabetes mellitus type 2 [5], eating disorders, glutaric aciduria type 1 [11], hair loss, heart attack [9], heart failure, high cholesterol or triglycerides, hyperthyroidism, HIV/AIDS, infertility in males, irregular heart beat (arrhythmia), leg ulcers, Lyme disease, migraine, myocarditis (inflammation of the heart muscle) or nonalcoholic liver disease, or in improving memory, promoting weight loss, slowing down aging or as an antidote in valproic acid overdose.

NOTE: Healthy people, including strict vegetarians (vegans), have no firmly confirmed benefits from taking L-carnitine supplements.

L-Carnitine Safety: Side Effects, Toxicity

L-carnitine supplements taken by mouth or as injections in recommended doses are LIKELY SAFE for most people. Toxicity from L-carnitine overdose has not been reported, so far.

Side effects of L-carnitine in doses 3 g/day or more may include nausea, stomach upset, heartburn, vomiting, diarrhea, muscle weakness (in hemodialysis patients) and increased frequency of seizures (in patients with epilepsy) and fishy odor of the breath, sweat and urine [2,4].

Pregnancy and breastfeeding. Not enough studies about the safety of L-carnitine supplements during pregnancy and breastfeeding have been done so far, so women in these periods should avoid them.

L-Carnitine-Drug Interactions

  • L-carnitine might increase the effectiveness of acenocoumarol and warrfarin (drugs to prevent blood clotting) and might thus increase the risk of bleeding [4]
  • L-carnitine may decrease the effectiveness of thyroid hormones [4]

  1. Carnitine: the science behind a conditionally essential nutrient  National Institutes of Health, Office of Dietary Supplements
  2. L-carnitine  Linus Pauling Institute
  3. L-carnitine  PubChem
  4. L-carnitine  WebMD
  5. Vidal Casariego A et al, 2013, Metabolic effects of L-carnitine on type 2 diabetes mellitus: systematic review and meta-analysis  PubMed
  6. Delaney CL et al, 2013, A systematic review to evaluate the effectiveness of carnitine supplementation in improving walking performance among individuals with intermittent claudication  PubMed
  7. Li S et al, 2015, Acetyl-L-carnitine in the treatment of peripheral neuropathic pain: a systematic review and meta-analysis of randomized controlled trials  PubMed
  8. Hurot JM et al, 2002, Effects of L-carnitine supplementation in maintenance hemodialysis patients: a systematic review  PubMed
  9. DiNicolantonio JJ et al, 2013, L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis  PubMed
  10. Brass EP et al, 2013, A systematic review and meta-analysis of propionyl-L-carnitine effects on exercise performance in patients with claudication  PubMed Health
  11. van Vliet D et al, 2014, Single amino acid supplementation in aminoacidopathies: a systematic review  PubMed Central

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