L-Carnitine: benefits, dosage, contraindications
Family or group:
Amino acids
Indications
Scoring methodology
EFSA approval.
Male fertility disorders ✪✪✪✪✪
Although some clinical research has produced conflicting results, most clinical studies show that daily intake of L-carnitine at 2 to 3 grams in divided doses for up to 24 weeks, with or without acetyl-L-carnitine at 1 gram per day, increases sperm count and motility in men with infertility of various etiologies. nn
Posologie
Oral
2 - 3 g
6 - months
Men, Seniors
Synergies
A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and l-acetyl-carnitine treatment in men with asthenozoospermia.
Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial
[Clinical efficacy of combined L-carnitine and acetyl-L-carnitine on idiopathic asthenospermia].
Cinnoxicam and L-carnitine/acetyl-L-carnitine treatment for idiopathic and varicocele-associated oligoasthenospermia.
[Short-term medication of L-carnitine before intracytoplasmic sperm injection for infertile men with oligoasthenozoospermia]
L-carnitine in idiopathic asthenozoospermia: a multicenter study. Italian Study Group on Carnitine and Male Infertility
[Treatment with carnitine, acetyl carnitine, L-arginine and ginseng improves sperm motility and sexual health in men with asthenopermia]
The efficacy of combined l-carnitine and l-acetyl carnitine in men with idiopathic oligoasthenoteratozoospermia: A systematic review and meta-analysis
Does L-carnitine therapy add any extra benefit to standard inguinal varicocelectomy in terms of deoxyribonucleic acid damage or sperm quality factor indices: a randomized study
Effect of L-carnitine and/or L-acetyl-carnitine in nutrition treatment for male infertility: a systematic review
Angina pectoris ✪✪✪✪✪
Several small clinical trials conducted in patients with chronic stable angina or cardiac syndrome show that oral (or intravenous) L-carnitine appears to improve exercise tolerance and the time to onset of angina pectoris compared with placebo. Oral doses of L-carnitine have ranged from 900 mg to 2 g per day, given as single or divided doses for 2 weeks to 6 months.
Posologie
Orally
900 - 2000 mg
The therapeutic effect of L-carnitine in patients with exercise-induced stable angina: a controlled study
L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis
Effects of L-carnitine on exercise tolerance in patients with stable angina pectoris
Propionyl-L-carnitine: a new compound in the metabolic approach to the treatment of effort angina
L-carnitine moderately improves the exercise tolerance in chronic stable angina
Dyslipidemia ✪✪✪✪✪
Meta-analyses of clinical research show that L-carnitine, taken orally at 750 mg to 3 g per day, appears to reduce total cholesterol, low-density lipoprotein cholesterol (LDL), and triglycerides, while increasing high-density lipoprotein cholesterol (HDL). However, these effects are modest. Some research has also evaluated the benefits of L-carnitine in people with hyperlipidemia and elevated lipoprotein(a) levels or in those on hemodialysis. Preliminary clinical research and a meta-analysis of clinical research in these populations show that taking L-carnitine at 1 to 2 g per day for 8 to 24 weeks reduces lipoprotein(a) levels. It is not known whether L-carnitine reduces the risk of cardiovascular events in patients with hyperlipidemia.
Posologie
Oral
750 - 3000 mg
Efficacy of L-carnitine supplementation for management of blood lipids: A systematic review and dose-response meta-analysis of randomized controlled trials
Impact of L-carnitine on plasma lipoprotein(a) concentrations: A systematic review and meta-analysis of randomized controlled trials
Polycystic ovary syndrome ✪✪✪✪✪
Some clinical research conducted in adults with PCOS who are clomiphene-resistant shows that taking 3 g of L-carnitine per day, from the third day of the menstrual cycle until the day of the pregnancy test, in combination with clomiphene, increases ovulation and pregnancy rates compared with placebo and clomiphene. The ovulation rate was 47% higher compared with placebo. Total cholesterol and low-density lipoprotein cholesterol levels were also improved. Clinical research also shows that taking 3 g of L-carnitine per day orally, in addition to clomiphene, is as effective as taking 600 mg of N-acetylcysteine orally three times a day, in addition to clomiphene, for improving ovulation and pregnancy rates. Another clinical trial shows that adding 3 grams of L-carnitine per day for 3 months to standard treatment with clomiphene plus metformin improves menstrual regularity by 20%, ovulation rate by 24%, and pregnancy rate by 21% compared with placebo.
Posologie
Oral
3 g
Adding L-carnitine in clomiphene-resistant PCOS women improves ovulation quality and pregnancy rate. A randomized clinical trial
L-carnitine plus metformin in clomiphene-resistant obese PCOS women, reproductive and metabolic effects: a randomized clinical trial
Liver disorders ✪✪✪✪✪
L-carnitine appears to be highly useful in liver diseases where it reduces ammonia levels, the symptoms of hepatic encephalopathy, and various markers of poor liver function:nn- In patients with cirrhosis.nn- In valproic acid-induced toxicities.nn- In patients with hepatitis.nnnnnn
Posologie
Orally
2 g
L-carnitine supplementation improves hematological pattern in patients affected by HCV treated with Peg interferon-α 2b plus ribavirin
L-carnitine treatment reduces steatosis in patients with chronic hepatitis C treated with alpha-interferon and ribavirin
The effect of carnitine supplementation in valproate-induced hyperammonemia
Efficacy and safety of entecavir plus carnitine complex (GODEX®) compared to entecavir monotherapy in patients with ALT-elevated chronic hepatitis B: randomized, multicenter open-label trials. The GOAL study
Effect of L-carnitine on health-related quality of life in patients with liver cirrhosis
Effect of L-carnitine supplementation on acute valproate intoxication
Sudden valproate-induced hyperammonemia managed with L-carnitine in a medically healthy bipolar patient: Essential review of the literature and case report
The role of carnitine supplementation during valproic acid therapy
Can L-carnitine supplementation and exercise improve muscle complications in patients with liver cirrhosis who receive branched-chain amino acid supplementation?
Effects of L-carnitine in patients with hepatic encephalopathy
Sports performance ✪✪✪✪✪
Maximal exercise in trained athletes has been associated with a decrease in plasma L-carnitine levels. Theoretically, restoring these levels through L-carnitine supplementation could have beneficial effects. However, clinical studies examining the use of L-carnitine for athletic performance have reported conflicting results. Some clinical studies show that taking 2 g of L-carnitine daily for up to 6 weeks improves athletic performance and endurance and reduces post-exercise muscle soreness in male athletes and healthy untrained men. Some studies show that taking 4 g per day for 2 weeks can decrease lactate accumulation and increase oxygen uptake, power output, and time to the anabolic threshold during exercise. However, other studies have been unable to confirm these results. These discrepancies may be related to small study sizes, short treatment durations, and variable dosing regimens.
Posologie
Oral route
2 - 4 g
The effect of oral supplementation with L-carnitine on maximum and submaximum exercise capacity
Carnitine in muscle, serum, and urine of nonprofessional athletes: effects of physical exercise, training, and L-carnitine administration
The effects of acute L-carnitine administration on ventilatory breakpoint and exercise performanceduring incremental exercise
Effects of Citric Acid and l-Carnitine on Physical Fatigue
Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double-blind crossover field study
THE EFFECT OF L-CARNITINE SUPPLEMENTATION ON 1500 m RUNNING PERFORMANCE
The effects of L-carnitine supplementation on performance during interval swimming
Muscular dystrophy ✪✪✪✪✪
A small clinical trial conducted in women aged 65 to 70, active and in good health, shows that daily intake of L-carnitine, in the form of L-carnitine-L-tartrate 1500 mg, for 24 weeks does not improve muscle strength or mass compared with placebo. However, in frailer adults aged 75 and over, taking 2 to 4 g of L-carnitine per day for 1 to 6 months increases muscle mass by about 2 to 4 kg compared with placebo.
Posologie
Orally
1.5 g
Levocarnitine administration in elderly subjects with rapid muscle fatigue: effect on body composition, lipid profile and fatigue
l-Carnitine Supplementation in Older Women. A Pilot Study on Aging Skeletal Muscle Mass and Function
Muscle pain ✪✪✪✪✪
Results from most small clinical trials, considered alone or combined via a meta-analysis, show that taking 1 to 3 grams of L-carnitine per day for about 3 weeks modestly reduces exercise-induced muscle pain, particularly in the 24 to 48-hour period after exercise. The benefits can last up to 96 hours after exercise. Levels of creatine kinase, lactate dehydrogenase, and myoglobin also appear to improve with L-carnitine supplementation, reflecting a reduction in muscle damage.
Posologie
Orally
1 g
L-carnitine L-tartrate supplementation favorably affects biochemical markers of recovery from physical exertion in middle-aged men and women
Effects of prolonged L-carnitine administration on delayed muscle pain and CK release after eccentric effort
Responses of criterion variables to different supplemental doses of L-carnitine L-tartrate
Obesity ✪✪✪✪✪
Meta-analyses of clinical trials show that daily intake of 250 mg to 4 g of L-carnitine slightly reduces body weight and body mass index (BMI) compared with a control group. nnHowever, subgroup analyses show that L-carnitine reduces BMI and weight only in overweight or obese patients. The intake of L-carnitine had no effect on weight or BMI in patients with a BMI less than or equal to 25 kg/m2. nnOther subgroup analyses show that even among overweight or obese individuals, there was no effect on BMI.nnL-carnitine has also been evaluated in combination with weight-loss medications. Clinical research shows that taking 2 g of L-carnitine per day in combination with orlistat 360 mg per day or sibutramine 10 mg per day for 1 year reduced body weight and BMI compared with orlistat or sibutramine alone in obese adults with type 2 diabetes.nn
Posologie
Orally
2 g
Effects of combination of sibutramine and L-carnitine compared with sibutramine monotherapy on inflammatory parameters in diabetic patients
Orlistat and L-carnitine compared to orlistat alone on insulin resistance in obese diabetic patients
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
The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials
Beneficial effects of l-carnitine supplementation for weight management in overweight and obese adults: An updated systematic review and dose-response meta-analysis of randomized controlled trials
Comparison between orlistat plus l-carnitine and orlistat alone on inflammation parameters in obese diabetic patients
Properties
Fertility effects
Carnitine concentrations are extremely high in the epididymis and in spermatozoa, suggesting a role for carnitine in male reproductive function. The epididymis derives the majority of its energy needs from lipids, as do spermatozoa during transport through the epididymis. After ejaculation, spermatozoa depend on glycolysis of glucose and fructose and on oxidation of lactate and pyruvate. Carnitine (in the form of acetylcarnitine, derived from pyruvate) serves as an easily available substrate. The motility of ejaculated spermatozoa is positively correlated with acetylcarnitine content. In human semen, high concentrations of carnitine are essential for the energetic metabolism of spermatozoa. Several studies have shown that the level of free carnitine in seminal fluid is strongly correlated with sperm count and motility. The lower the carnitine content, the more likely a man is to be infertile.
Usages associés
Cardiovascular
Normal cardiac function depends largely on adequate concentrations of carnitine. Although the normal heart stores more carnitine than it needs, if the heart does not receive sufficient oxygen, carnitine levels decrease rapidly. This lack of oxygen leads to decreased energy production in the heart and an increased risk of angina pectoris and heart disease. Carnitine supplementation increases carnitine levels in the heart and prevents the production of toxic fatty acid metabolites, and it also increases levels of antioxidant enzymes. In in vitro research, L-carnitine protects against hypertension-induced cardiac remodeling and against proliferation and inflammation of cardiac fibroblasts.
Usages associés
Musculoskeletal effects
It has been shown in vitro that L-carnitine increases the oxidative capacity of the liver and muscles during exercise and promotes the recovery of muscle fiber thickness. The benefits of L-carnitine also include intermittent oxidative stress, possibly related to antioxidant effects, resulting in delayed muscle fatigue and an increased time to exhaustion.
Usages associés
Anti-aging
It is thought that carnitine levels decline with age and may contribute to age-associated frailty. Laboratory research suggests that the anti-aging benefits of L-carnitine may be related to its effects on oxidative damage. In animal models of aging, carnitine prevented the age-related decline in mitochondrial activity. Acetyl-L-carnitine (LAC), a molecule composed of acetic acid and L-carnitine, is significantly more active than other forms of carnitine in the brain. Indeed, it is structurally related to acetylcholine, a major neurotransmitter responsible for memory and healthy brain function. In Alzheimer's disease, and in the normally aging human brain, there is a defect in the use of acetylcholine. Researchers have shown that LAC mimics acetylcholine and is beneficial not only in patients with early-stage Alzheimer's disease but also in depressed elderly patients or those suffering from memory disorders. It has also been shown to act as a powerful antioxidant within brain cells by stabilizing cell membranes and improving energy production in brain cells.
Usages associés
Antioxidant
L-carnitine may have antioxidant properties. L-carnitine has a metal-chelating capacity, which interferes with the formation of reactive oxygen species and stabilizes the free radicals that form. In human research, L-carnitine has been shown to increase glutathione levels, decrease malondialdehyde levels (a marker of lipid peroxidation), and increase superoxide dismutase activity (an enzyme that traps free radicals).
Hypoglycemic
Diabetic patients generally have a deficient carnitine status. Studies have revealed a relationship between low carnitine status and increased plasma fatty acids, which negatively affect insulin action. Preliminary studies suggest that intravenous infusions of L-carnitine may produce a short-term improvement in insulin sensitivity in people with type 2 diabetes. Other preliminary clinical research suggests that L-carnitine may also improve glucose utilization, possibly by increasing the expression of glycolytic and gluconeogenic enzymes.
Hypolipidemic
Although preliminary clinical research suggests that L-carnitine does not reduce triglyceride levels in people with hypertriglyceridemia, some evidence suggests beneficial effects on lipoprotein(a) levels. Indeed, L-carnitine may decrease the production of lipoprotein(a) in the liver by increasing the breakdown of fatty acids. This could also increase the transport of fatty acids into the mitochondria, which may result in decreased availability of fatty acids for lipid synthesis.
Usages associés
Safe dosage
Adults aged 18 years and older: 2 g
When used orally and appropriately, L-carnitine has been used safely in clinical trials lasting up to 12 months. Avoid using D-carnitine and DL-carnitine at the same time as L-carnitine. Indeed, these forms of carnitine can act as competitive inhibitors of L-carnitine, thus causing symptoms of L-carnitine deficiency. Although much higher concentrations have been tested without adverse effects and may be safe, data for doses above 2000 mg/day are insufficient to conclude with certainty about long-term safety.
Infants up to 6 months: 50 mg/kg - 100 mg/kg
When used orally or intravenously and appropriately, L-carnitine has been used safely in preterm infants and children up to 6 months at a dose of 50 to 100 mg/kg/day.
Breastfeeding woman:
La L-carnitine is naturally secreted into breast milk. Additional oral doses of L-carnitine have been given to breastfeeding mothers and to infants fed with formula without reported adverse effects. The effects of high doses used during breastfeeding are unknown.
Interactions
Médicaments
Cefditoren: moderate interaction
Cefditoren pivoxil is a prodrug that is converted to cefditoren and pivalate in the body. The latter, when combined with L-carnitine, would be excreted in the urine, which increases the loss of L-carnitine from the body. Thus, short courses of cefditoren can decrease blood concentrations of L-carnitine, but tissue levels are unlikely to be affected. Treatment lasting one to two months may lead to a decrease of L-carnitine in the muscles, and treatment lasting six months or more may lead to deficiency symptoms. Systematic supplementation with L-carnitine is therefore not necessary unless the treatment is prolonged or the patient has other factors contributing to low L-carnitine reserves.
Pivampicillin: moderate interaction
Pivampicillin is a prodrug that releases the active antibiotic and pivalate into the body. Pivalate binds to carnitine and is excreted in the urine, which increases the body's losses of L-carnitine. With short-term treatment, blood carnitine decreases, but tissue levels do not appear to be affected. Treatment for 1 to 2 months leads to a decrease in muscle carnitine, and treatment for 6 months or longer may cause symptoms of carnitine deficiency. Routine carnitine supplementation is not necessary unless treatment is prolonged or the patient has other factors contributing to depleted L-carnitine stores.
Valproic acid: moderate interaction
Valproic acid can reduce carnitine levels in the blood and tissues. Indeed, it interferes with the biosynthesis of L-carnitine in the liver and the formation of a valproylcarnitine ester that is excreted in the urine, thereby reducing the tubular reabsorption of free carnitine. Thus, reduced levels of L-carnitine are not clinically significant in most people taking valproic acid. However, some patients may be at increased risk of deficiency with such an association, which can contribute to the development of hyperammonemia and drug-associated hepatotoxicity. A significant deficiency in L-carnitine can result in serious neurological problems such as intellectual disability in children. Some experts recommend L-carnitine supplements for people with risk factors who are required to take valproic acid. However, L-carnitine supplementation is not necessary for most people taking valproic acid who are otherwise healthy and follow a balanced diet.
Besifovir: strong interaction
Clinical studies have shown that daily intake of 90 to 150 mg of besifovir reduced serum concentrations of free and total L-carnitine below normal values in about 94% of patients.
Acenocoumarol: moderate interaction
Taking L-carnitine at a dose of 1 g per day appears to significantly increase the anticoagulant effects of acenocoumarol.
Hormones: moderate interaction
L-carnitine appears to act as a peripheral antagonist of thyroid hormones by inhibiting their entry into the cell nucleus. It also appears to lessen some symptoms of hyperthyroidism. Theoretically, taking L-carnitine could reduce the effectiveness of thyroid hormone replacement.
Plantes ou autres actifs
L-Carnitine: moderate interaction
D-carnitine could compete with L-carnitine in active transport systems. Taking D-carnitine could cause symptoms of L-carnitine deficiency.
Precautions
Pregnancy: avoid
L-carnitine should be avoided during pregnancy due to a lack of reliable and sufficient information.
Hypothyroidism: avoid
L-carnitine appears to act as a peripheral antagonist of thyroid hormones by inhibiting their entry into the cell nucleus. Theoretically, taking L-carnitine could worsen the symptoms of hypothyroidism.
Epilepsy: avoid
An increase in the frequency or severity of seizures has been reported in people with a prior history of seizures who have used L-carnitine orally or intravenously.
