L-Carnitine

What is L-carnitine and what does it do in the body?

According to NIH ODS, carnitine is a general term for several compounds derived from an amino acid, such as L-carnitine, acetyl-L-carnitine, and propionyl-L-carnitine. It is abundant in animal foods, is sold as a supplement, and is also synthesized from lysine and methionine in the liver, kidney, and brain. Carnitine is a “conditionally essential” nutrient only because, under certain conditions such as prematurity or kidney dysfunction, the requirement exceeds synthesis capacity. It plays a key role in energy production: it is an essential cofactor that helps transport long-chain fatty acids into mitochondria, and it also helps carry some toxic compounds out of mitochondria. ^[1]

About 95% of the body’s carnitine is stored in heart and skeletal muscle, most of the rest is found in the liver and kidney, and only about 0.5% is in circulating plasma; excess plasma carnitine is excreted in urine. The body is stated to need about 15 mg of carnitine per day from food and synthesis. Endogenous synthesis is not affected by the amount of carnitine in the diet and is enough to meet the needs of healthy people; a strict vegetarian weighing 165 lb (≈75 kg) synthesizes about 14.4 mg per day. ^[1] ODS therefore states that healthy children and adults do not need to obtain carnitine from food or supplements; the FNB concluded in 1989 that carnitine is not an essential nutrient and did not set a DRI. ^[1]

Which foods contain carnitine?

Carnitine is found in animal products, especially red meat; poultry, fish, and dairy products also provide some, while vegetables, fruits, and grains contain negligible amounts. The bioavailability of dietary carnitine is about 63–75%. A typical omnivorous diet provides about 24–145 mg of carnitine per day to a person weighing 165 lb, and a vegan diet about 1.2 mg. Data on carnitine in foods are limited; USDA FoodData Central does not list carnitine content. ^[1]

Supplements are sold as carnitine alone or together with other ingredients; the two main forms are L-carnitine and acetyl-L-carnitine, and the amount in products varies from about 3 mg to 5,000 mg. Absorption of supplemental L-carnitine is about 14–18%; this is much lower than that of L-carnitine from food. The bioavailability of acetyl-L-carnitine has not been well studied. ^[1]

Who gets carnitine deficiency?

According to ODS, there are two types of deficiency. Primary carnitine deficiency is a genetic disorder affecting the cells’ carnitine transporter system and mostly appears in infancy or early childhood; epilepsy and encephalopathy can be seen in infants, seizures, irregular heartbeat, and breathing problems in adolescents and young adults, and myopathy, rhabdomyolysis, cardiomyopathy, or sudden death in older people; some individuals have no symptoms, but all are at increased risk of heart failure, liver disease, and coma. The review published in Orphanet reports that this disease is caused by recessive mutations in the SLC22A5 gene (OCTN2 transporter), that its frequency in the U.S., based on newborn screening, is about 1 in 50,000, and that diagnosis is made by low plasma free carnitine concentration (below 5 µM; normal 25–50 µM), reduced fibroblast carnitine transport, and genetic testing; the primary treatment is oral levocarnitine replacement, and the long-term prognosis is favorable as long as replacement is continued. ^{[1] [8]}

Secondary deficiency results from diseases that reduce carnitine synthesis or increase its excretion, such as chronic kidney failure, or from chronic use of pivalate-containing drugs. As a general threshold, ODS considers a plasma free carnitine concentration of 20 µmol/L or below and a total carnitine of 30 µmol/L or below to be abnormally low; these thresholds and the diagnostic value for primary deficiency in the Orphanet review belong to different contexts. ^[1] Premature infants are also a risk group; ODS reports that a Cochrane review of 6 randomized studies on parenteral nutrition in newborns did not support the use of parenteral carnitine to improve lipid utilization or weight gain. It is stated that in patients with kidney disease and on hemodialysis, high-dose (mostly injected) carnitine may correct some symptoms, but most studies were small and not double-blind. ^[1] These treatments require specialist follow-up, and supplements marketed as sports or weight-loss products should not be confused with them.

Does L-carnitine help weight loss?

The 2016 meta-analysis by Pooyandjoo and colleagues combined 9 studies of sufficient methodological quality (911 people in total) examining the effect of carnitine on weight loss in adults. People taking carnitine lost significantly more weight than the control group (mean difference −1.33 kg; 95% CI −2.09 to −0.57), and body mass index decreased (−0.47 kg/m²; 95% CI −0.88 to −0.05). Meta-regression showed that the magnitude of weight loss with carnitine decreased significantly as duration of consumption increased (P=0.002). ^[2] As ODS notes, weight is a secondary outcome in most studies and results are uncertain: in 258 adults with type 2 diabetes, when 2 g/day of carnitine was used together with orlistat for one year, more weight was lost than with orlistat alone (11.3 kg vs. 9.5 kg), and in 94 people with newly diagnosed type 2 diabetes, carnitine alone did not affect weight over 6 months. ^[1]

This row is therefore at level C: the effect is statistically significant but small and diminishes over time.

Does L-carnitine improve athletic performance?

ODS states that carnitine helps preserve muscle glycogen, supports fat oxidation, and reduces lactate accumulation, whereas findings on the effect of supplementation on athletic performance are mixed. The examples it reports show this picture: in 14 recreational athletes, carnitine tartrate added to a carbohydrate solution for 24 weeks gave lower perceived exertion (Borg scale 14.0 vs. 16.2) at workloads of 50% and 80% of VO2max; in 8 omnivorous and 16 vegetarian men, 12 weeks of carnitine did not affect VO2max, blood lactate, muscle energy metabolism, or physical performance, and increased muscle carnitine stores by about 13% only in vegetarians (not in omnivores). ^[1]

ODS also reports a 2018 review: in 11 studies covering 251 well-trained athletes, lactate and heart rate decreased and VO2max and recovery improved in some studies, whereas performance did not change in others; in recreationally active adults, results are similarly mixed in 17 studies (237 people). In a systematic review of 11 RCTs covering 203 physically active, untrained adults, results are also mixed, and no study found improvement in moderate-intensity exercise performance. As an overall result, ODS rates the evidence for performance enhancement as mixed and requiring further research. ^[1] This row is given as D.

Does L-carnitine affect blood sugar?

The meta-analysis by Zamani and colleagues combined 41 RCTs (2,900 people) in adults taking oral L-carnitine for at least seven days. Fasting blood sugar decreased by −3.22 mg/dL (95% CI −5.21 to −1.23), HbA1c by −0.27% (−0.47 to −0.07), and HOMA-IR by −0.73 (−1.21 to −0.25); heterogeneity is very high (I² 88.6%, 90.1%, and 98.2%, respectively). The effect is marked in studies with baseline fasting glucose of 100 mg/dL and above, duration of 12 weeks and above, and daily dose of 2 g and above, and in overweight/obese participants and people with diabetes. ^[3] ODS states that most studies in the same area were conducted in people with disease, such as type 2 diabetes, obesity, polycystic ovary syndrome, or fatty liver. ^[1] Because the results are inconsistent and based on populations with disease, the row is at level C.

Is there evidence for L-carnitine in the heart and dementia?

Acute myocardial infarction. The 2013 meta-analysis by DiNicolantonio and colleagues combined 13 controlled studies (3,629 people) comparing L-carnitine with placebo or control in patients with acute myocardial infarction. With carnitine, a reduction in all-cause mortality (OR 0.73; 95% CI 0.54–0.99; RR 0.78; 95% CI 0.60–1.00; P=0.05), a reduction in ventricular arrhythmia (RR 0.35; 0.21–0.58), and a reduction in the development of angina (RR 0.60; 0.50–0.72) were reported; no reduction was seen in heart failure (RR 0.85; 0.67–1.09) or reinfarction (RR 0.78; 0.41–1.48). ^[4] These findings belong to a clinical context under physician supervision and are not evidence of heart protection for healthy people.

Acetyl-L-carnitine and dementia. The Cochrane review by Hudson and Tabet evaluated 11 double-blind studies comparing acetyl-L-carnitine with placebo in people with Alzheimer’s disease. A significant difference in favor of acetyl-L-carnitine in clinical global impression was found at weeks 12 and 24 (OR 2.33; 95% CI 1.25–4.35 and OR 3.91; 95% CI 1.32–11.54), and not at week 52; no objective benefit was seen in cognition, dementia severity, and functional ability. The authors state that the significant result may be due to chance given the many comparisons and that there is no evidence to recommend routine use. ^[5]

Why are TMAO and cardiovascular safety debated?

The 2013 study by Koeth and colleagues showed that omnivorous humans produce more TMAO than vegans and vegetarians after ingesting L-carnitine, and that this production depends on the gut microbiota. In 2,595 people undergoing cardiac evaluation, plasma L-carnitine level predicted prevalent cardiovascular disease and risk of major adverse cardiac events (myocardial infarction, stroke, or death) only in those with concurrently high TMAO levels. In mice, chronic carnitine supplementation increased TMAO production and the development of atherosclerosis; this mouse finding is not a human result. ^[6]

The 2022 RCT by Johri and colleagues compared 2 g/day of L-carnitine with placebo for 6 months in 157 participants (76 carnitine, 81 placebo) with metabolic syndrome and carotid plaque volume of 50 mm³ and above. The change in total plaque volume did not differ between groups; among exploratory measures, carotid atherosclerotic stenosis increased 9.3% more in the carnitine group than in the placebo group (95% CI 1.6–17.6; p=0.02), and total cholesterol and LDL cholesterol rose more in the carnitine group. The authors interpreted this as a concerning progression in carotid plaque stenosis. The study is two-center, and the authors reported no conflict of interest. ^[7] In reporting the same study, ODS links the 9.3% stenosis difference to men who ate less red meat and had lower baseline stenosis and plaque volume; the article’s abstract, by contrast, reports this difference across all arms. ^[1] This row is rated E: no benefit was shown, and the safety question remains open.

Is carnitine supplementation safe, and with which drugs does it interact?

ODS reports that no upper limit (UL) has been set for carnitine; that carnitine supplementation of about 3 g per day can cause nausea, vomiting, abdominal cramps, diarrhea, and a fishy body odor; that muscle weakness has been reported in people with uremia and seizures in people with seizure disorders. It is stated that gut bacteria convert unabsorbed carnitine to TMAO and gamma-butyrobetaine, that this may increase cardiovascular risk, that the effect is more marked in meat eaters, and that the results are not fully understood. ^[1]

Pivalate-conjugated antibiotics (e.g., pivampicillin) can lead to carnitine depletion with chronic use; however, no disease due to carnitine deficiency has been reported in this population. Treatment with valproic acid, phenobarbital, phenytoin, and carbamazepine lowers blood carnitine levels; valproic acid can also cause hepatotoxicity and an increase in plasma ammonia. ODS states that intravenous L-carnitine may help in treating valproic acid toxicity and that the optimal regimen has not been determined. ^[1]

How is L-carnitine regulated in Türkiye?

Ministry of Agriculture and Forestry approval is mandatory for every dietary supplement to be marketed in Türkiye; approval applications for imported products can be made only to the Istanbul and Ankara Provincial Directorates. ^[10]

In the latest update of the Ministry’s Restricted Substances List for Dietary Supplements (September 21, 2026), the source in the “L-Carnitine” row is “chemical synthesis”; at most 1 g/day is written in the ages 4–10 daily intake column and at most 2 g/day in the age 11 and over column; the publication dates are January 22, 2016 for ages 11 and over and May 2, 2016 for ages 4–10. The list also has a separate “N-Acetyl Carnitine” row: source chemical synthesis, 2 g/day in the age 11 and over column, publication date May 2, 2016. ^[9] These limits are daily intake columns; they are not a value of the same kind as ODS’s “no UL” statement.

Evidence table: claim, population, and limits

This guide does not recommend personal doses. In kidney disease, a history of seizures, and regular medication use, the decision depends on individual assessment.