L-Carnitine: benefits, dosage, contraindications
Other name(s)
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Amino acids
Indications
Rating methodology
EFSA approval.
Male fertility disorders ✪✪✪✪✪
Although some clinical research has produced conflicting results, most clinical studies show that daily intake of 2 to 3 grams of L-carnitine in divided doses for up to 24 weeks, with or without 1 gram of acetyl-L-carnitine per day, increases sperm count and motility in men with infertility of various etiologies.
Posologie
Oral route
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 ✪✪✪✪✪
Several small clinical trials conducted in patients with chronic stable angina or cardiac syndrome show that oral (or intravenous) intake of L-carnitine seems to improve exercise tolerance and delay the onset of angina compared to placebo. Oral doses of L-carnitine ranged from 900 mg to 2 g per day in single or divided doses for 2 weeks to 6 months.
Posologie
Oral route
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, administered orally at 750 mg to 3 g per day, seems to reduce total cholesterol levels, low-density lipoprotein (LDL) cholesterol, and triglycerides, while increasing high-density lipoprotein (HDL) cholesterol. 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 those undergoing 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 route
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 clomiphene-resistant PCOS shows that taking 3 g of L-carnitine per day, from day three of the menstrual cycle to the day of the pregnancy test, in combination with clomiphene, increases ovulation and pregnancy rates compared to placebo and clomiphene. The ovulation rate was 47% higher compared to placebo. Total cholesterol and low-density lipoprotein cholesterol levels also improved. Clinical research also shows that taking 3 g of L-carnitine per day orally, along with clomiphene, is as effective as taking 600 mg of N-acetylcysteine orally three times a day, along with clomiphene, to improve ovulation and pregnancy rates. Another clinical trial shows that adding 3 grams of L-carnitine per day for 3 months to the standard treatment of clomiphene plus metformin improves menstrual regularity by 20%, ovulation rate by 24%, and pregnancy rate by 21% compared to placebo.
Posologie
Oral route
3 g
Adding L-carnitine to clomiphene resistant PCOS women improves the quality of ovulation and the 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 seems to have significant utility in liver diseases where it reduces ammonia levels, symptoms of hepatic encephalopathy, and various markers of poor liver function: - In patients with cirrhosis. - In valproic acid-induced toxicities. - In patients with hepatitis.
Posologie
Oral route
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 hyperammonaemia
Efficacy and safety of entecavir plus carnitine complex (GODEX®) compared to entecavir monotherapy in patient 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 sports performance have reported mixed 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 untrained healthy 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 anaerobic threshold during exercise. However, other studies have not been able to confirm these results. These discrepancies may be related to the 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 among 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 to placebo. However, in weaker adults aged 75 and older, taking 2 to 4 g of L-carnitine per day for 1 to 6 months increases muscle mass by approximately 2 to 4 kg compared to 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 ✪✪✪✪✪
The results of most small clinical trials, considered alone or combined through meta-analysis, show that taking 1 to 3 grams of L-carnitine per day for about 3 weeks modestly reduces exercise-induced muscle pain, especially in the period of 24 to 48 hours 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 weight and body mass index (BMI) compared to a control group. However, subgroup analyses show that L-carnitine only reduces BMI and weight 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. Further subgroup analyses show that even in overweight or obese individuals, there was no effect on BMI. L-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 reduces body weight and BMI compared to orlistat or sibutramine alone in obese adults with type 2 diabetes.
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 effect
Carnitine concentrations are extremely high in the epididymis and sperm, suggesting a role for carnitine in male reproductive function. The epididymis derives most of its energy needs from lipids, as do sperm during transport through the epididymis. After ejaculation, spermatozoa depend on the glycolysis of glucose and fructose and the oxidation of lactate and pyruvate. Carnitine (as acetylcarnitine derived from pyruvate) serves as a readily available substrate. The motility of ejaculated sperm is positively correlated with acetylcarnitine content. In human semen, high concentrations of carnitine are essential for the energy metabolism of sperm. 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 sterile.
Usages associés
Cardiovascular
Normal heart function essentially depends on adequate concentrations of carnitine. Although the normal heart stores more carnitine than needed, if the heart does not have a good oxygen supply, carnitine levels decrease rapidly. This lack of oxygen leads to decreased energy production in the heart and an increased risk of angina and heart disease. Carnitine supplementation increases carnitine levels in the heart and prevents the production of toxic fatty acid metabolites, as well as increasing levels of antioxidant enzymes. In in vitro research, L-carnitine protects against cardiac remodeling induced by hypertension or proliferation and inflammation of cardiac fibroblasts.
Usages associés
Musculoskeletal effects
It has been demonstrated 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 increased time to exhaustion.
Usages associés
Anti-aging
Carnitine levels are thought to decrease with age and may contribute to age-associated frailty. Laboratory research suggests that the anti-aging benefits of L-carnitine may be associated with its benefits on oxidative damage. In animal aging models, carnitine has 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. It is structurally linked to acetylcholine, a major neurotransmitter responsible for memory and proper brain function. In Alzheimer's disease and in normal aging human brains, there is a defect in acetylcholine utilization. Researchers have shown that LAC mimics acetylcholine and is beneficial not only in early-stage Alzheimer's patients but also in elderly, depressed patients suffering from memory disorders. It has also been shown to act as a powerful antioxidant in brain cells by stabilizing cell membranes and enhancing energy production in brain cells.
Usages associés
Antioxidant
L-carnitine may possess antioxidant properties. L-carnitine has a metal chelation capacity, which interferes with the formation of reactive oxygen species and stabilizes 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 the activity of superoxide dismutase (an enzyme that scavenges 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 L-carnitine infusions may produce short-term improvements in insulin sensitivity in people with type 2 diabetes. Other preliminary clinical research suggests that L-carnitine may also improve glucose use, possibly by increasing the expression of glycolytic and gluconeogenic enzymes.
Hypolipidemic
While 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 fatty acid breakdown. It may also increase the transport of fatty acids into the mitochondria, leading to reduced availability of fatty acids for lipid synthesis.
Usages associés
Safety dosage
Adult from 18 years: 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. These forms of carnitine can act as competitive inhibitors of L-carnitine, causing symptoms of L-carnitine deficiency. While much higher concentrations have been tested without adverse effects and may be safe, the data for doses exceeding 2000 mg/day are insufficient to conclude with certainty on long-term safety.
Infant 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 and children up to 6 months at a dose of 50 to 100 mg/kg/day.
Breastfeeding woman:
L-carnitine is naturally secreted in breast milk. Supplemental oral doses of L-carnitine have been given to breast milk and formula milk without reported adverse effects. The effects of high doses used during breastfeeding are unknown.
Interactions
Médicaments
Cefditoren: moderate interaction
Cefditoren pivoxil is a prodrug converted into cefditoren and pivalate in the body. Pivalate, when combined with L-carnitine, would be excreted in the urine, increasing L-carnitine loss from the body. Therefore, short courses of cefditoren might lower blood concentrations of L-carnitine, but tissue levels are unlikely to be affected. A treatment lasting one to two months may lead to decreased muscular L-carnitine, and treatment of six months or more can lead to deficiency symptoms. Systematic L-carnitine supplementation is thus not necessary unless the treatment is prolonged or if the patient has other factors contributing to weak L-carnitine reserves.
Pivampicillin: moderate interaction
Pivampicillin are prodrugs that release the active antibiotic and pivalate in the body. Pivalate combines with carnitine and is excreted in the urine, increasing L-carnitine loss from the body. In short-term treatments, carnitine blood levels decrease, but tissue levels are not affected. A treatment of 1-2 months results in reduced muscular carnitine, and a treatment of 6 months or more may cause carnitine deficiency symptoms. Systematic carnitine supplementation is not needed unless the treatment is prolonged or if the patient has other factors contributing to weak L-carnitine reserves.
Valproic acid: moderate interaction
Valproic acid can reduce carnitine levels in the blood and tissues. It interferes with L-carnitine biosynthesis in the liver and forms a valproylcarnitine ester that is excreted in the urine, thus reducing tubular reabsorption of free carnitine. As a result, reduced L-carnitine levels are not clinically significant for most people taking valproic acid. However, some patients may be at increased risk of deficiency, contributing to drug-associated hyperammonemia and hepatotoxicity. Significant L-carnitine deficiency can lead to severe neurological problems such as mental retardation in children. Some experts recommend L-carnitine supplements for those with risk factors who must take valproic acid. Nonetheless, L-carnitine supplementation is not necessary for most individuals taking valproic acid who are otherwise healthy and follow a balanced diet.
Besifovir: strong interaction
Clinical studies have shown that taking 90 to 150 mg of besifovir daily decreases free and total serum L-carnitine concentrations below normal values in about 94% of patients.
Acenocoumarol: moderate interaction
Taking 1 g per day of L-carnitine seems to significantly enhance the anticoagulant effects of acenocoumarol.
Hormones: moderate interaction
L-carnitine seems to act as a peripheral antagonist of thyroid hormones by inhibiting their entry into the cell nucleus. It also appears to attenuate some symptoms of hyperthyroidism. Theoretically, taking L-carnitine could diminish 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
Pregnant woman: avoid
L-carnitine should be avoided in pregnant women due to 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 nucleus of cells. Theoretically, taking L-carnitine could worsen hypothyroidism symptoms.
Epilepsy: avoid
An increase in the frequency or severity of seizures has been reported in individuals with a history of seizures taking L-carnitine orally or intravenously.
