As a nutrition support pharmacist, you will see L-carnitine, an amino acid, listed as an ingredient in some supplements and energy drinks. The debate's heating up on the safety and benefits of L-carnitine...
The body can make L-carnitine (It is synthesized by the liver and kidneys from lysine and methionine. In fact, the body can synthesize all the L-carnitine it needs, so it's not considered an essential nutrient), OR get it from foods, especially red meat and dairy products. There's no need for most people to take supplements of this amino acid compound. L-carnitine plays a role in the use of dietary fuel. It helps facilitate the entry of long chain fatty acids into cellular mitochondria for oxidation and energy production. All of the tissues in the body use fatty acids for energy except for the brain. But L-carnitine is showing up in more supplements and energy drinks and is marketed for weight loss, fatigue, muscle growth, etc.
L-carnitine is available as a prescription product, Carnitol, in oral and IV formulations (see Table 1). L-carnitine is most commonly used at a dose of 2 grams daily. Doses ranging from 1-4 grams daily, most often taken in divided doses, have been used for up to 1 year. Doses of 6 grams or 50-100 mg/kg daily have been used for up to 6 months. For weight loss, ingestion of 2000 mg l-carnitine per day provides a modest reducing effect on body weight, BMI and fat mass, especially among adults with overweight/obesity.
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Don't let patients get caught up in the hype. Tell patients NOT to rely on L-carnitine supplements to increase endurance and athletic performance. A rare exception is patients with L-carnitine deficiency. In these very few cases, use the Rx version of L-carnitine (Carnitol, etc).
You will also hear concerns that gut flora can metabolize L-carnitine into atherogenic particles. When L-carnitine is administered orally, gut flora can metabolize it to a substance called TMAO (trimethylamine-N-oxide). TMAO plays a role in atherosclerosis and atherothrombogenesis. But explain that so far, there's not enough reliable evidence that L-carnitine increases cardiovascular risk.
| Table (1). L-Carnitine Dosage | |
|---|---|
| Indication | Dosage |
| Athletic performance | 3 or 4 g in prolonged time to exhaustion |
| Cardiovascular disease, secondary prevention | Oral maintenance doses of L-carnitine 2 to 6 g/day for up to 12 months have been used in clinical studies; some trials used oral or IV loading doses of 6 or 9 g/day for 5 to 7 days |
| Diabetes mellitus, type 2 | L-carnitine 2 g once daily for 1 year as a combination therapy with either orlistat or sibutramine. Other treatment options include an IV dose of acetyl-L-carnitine 5 mg/kg bolus loading dose followed by 0.025, 0.1, or 1 mg/kg constant infusion |
| Dyslipidemia | Combination therapy of L-carnitine 2 g once daily with orlistat in adults with type 2 diabetes. A regimen of 500 mg twice daily was given for 12 weeks for dyslipidemia in patients with coronary artery disease without comorbid diabetes, liver disease, or renal disease |
| Migraine prophylaxis | L-carnitine 500 mg/day administered orally for 12 weeks |
| Carnitine deficiency, Primary | tablet, 990 mg ORALLY 2 to 3 times daily 3 oral solution, initial, 1 gram ORALLY daily, titrate slowly to therapeutic response; average dose 1 to 3 g ORALLY daily for 50 kg adult |
| Carnitine deficiency, Secondary - Inborn error of metabolism |
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| Carnitine deficiency; Treatment and Prophylaxis - End-stage renal disease - Hemodialysis | Initial, 10 to 20 mg/kg (dry weight) over 2 to 3 min bolus injection after dialysis; subsequent dose titration determined by trough (predialysis) levocarnitine concentrations |
| This information from, https://www.dynamed.com/drug-monograph/levocarnitine | |
REFERENCES
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DiNicolantonio JJ, Lavie CJ, Fares H, Menezes AR, O'Keefe JH. L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis. Mayo Clin Proc. 2013 Jun;88(6):544-51. Available at: https://www.mayoclinicproceedings.org/article/S0025-6196(13)00127-4/fulltext
Office of Dietary Supplements. Dietary supplement fact sheet: Carnitine. June 15, 2006. Available at: http://ods.od.nih.gov/factsheets/Carnitine-HealthProfessional
Koeth RA, Wang Z, Levison BS, Buffa JA, Org E, Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, DiDonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, Hazen SL. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013 May;19(5):576-85. Available at: https://pubmed.ncbi.nlm.nih.gov/23563705
Talenezhad N, Mohammadi M, Ramezani-Jolfaie N, Mozaffari-Khosravi H, Salehi-Abargouei A. Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis. Clin Nutr ESPEN. 2020 Jun;37:9-23. Available at: https://pubmed.ncbi.nlm.nih.gov/32359762