It is used for weight loss and may have an impact on brain function. This article examines the potential risks and benefits of L-carnitine supplements and explains how this nutrient functions in your body.

L-carnitine is a nutrient and dietary supplement. The mitochondria act as engines within your cells, burning these fats to create usable energy. Your body can produce L-carnitine out of the amino acids lysine and methionine 2. For your body to produce it in sufficient amounts, you also need plenty of vitamin C 3.

In addition to the L-carnitine produced in your body, you can also obtain small amounts by eating animal products like meat or dairy products 2. Vegans or people with certain genetic issues may be unable to produce or obtain enough. This makes L-carnitine a conditionally essential nutrient 2.

L-carnitine is the standard biologically active form of carnitine, which is found in your body, foods, and most supplements.

For most people, acetyl-L-carnitine and L-carnitine seem to be the most effective for general use. In cells, it helps transport fatty acids into the mitochondria, where they can be burned for energy. L-carnitine may help increase mitochondrial function, which plays a key role in disease and healthy aging 1 , 10 , L-carnitine is an amino acid derivative that transports fatty acids into your cells to be processed for energy.

It is made by your body and also available as a supplement. One review of 37 studies found that L-carnitine supplementation significantly reduced body weight, body mass index BMI , and fat mass.

However, it had no effect on belly fat or body fat percentage Another analysis of nine studies — mostly in individuals with obesity or older adults — found that people lost an average of 2.

Furthermore, while it may aid in weight loss for some people, you may wish to consult with a dietician to develop a thorough diet and exercise regimen first. Some studies suggest that L-carnitine could help promote weight loss and fat loss.

However, more studies are needed. Some research suggests that the acetyl form, acetyl-L-carnitine ALCAR , may help prevent age-related mental decline and improve markers of learning In fact, according to one study, taking 1, milligrams mg of ALCAR daily for 28 weeks significantly improved brain function in people with dementia For instance, a review of two studies showed that taking L-carnitine for 3 days had no effect on markers of brain function — including reaction time, vigilance, immediate memory, and delayed recall — in young adults without cognitive impairment L-carnitine — specifically acetyl-L-carnitine — may have beneficial effects on brain function.

Still, more research is needed. For example, one review of 10 studies found that L-carnitine significantly reduced diastolic blood pressure, especially in people with overweight and obesity Another analysis of 17 studies showed that L-carnitine could improve heart function and decrease symptoms in people with congestive heart failure Additionally, a review showed that L-carnitine could reduce total and LDL bad cholesterol while increasing HDL good cholesterol in people at risk for heart disease The evidence is mixed when it comes to the effects of L-carnitine on sports performance, but it may offer some benefits.

This differs from supplements like caffeine or creatine , which can directly enhance sports performance 22 , A recent review of 41 studies concluded that L-carnitine supplementation could reduce fasting blood sugar and hemoglobin A1c a marker of long-term blood sugar levels while also improving insulin sensitivity in people with diabetes, overweight, or obesity According to the authors of the review, L-carnitine is believed to work by altering insulin receptors and changing the expression of specific genes that regulate sugar metabolism It may also help improve the function of beta cells, which are cells in the pancreas that are responsible for producing insulin In one review of 12 studies, acetyl-L-carnitine significantly reduced symptoms of depression compared with placebo Interestingly, several of the studies included in this review also found that acetyl-L-carnitine was as effective as antidepressant medications but caused fewer adverse effects Research suggests that L-carnitine may aid exercise performance and treat health conditions like heart disease, depression, and type 2 diabetes.

For most people, taking 2 grams g or less per day is relatively safe and free from any serious side effects Some research has also used doses of up to 4, mg per day However, there were some mild side effects, including heartburn and indigestion However, L-carnitine supplements may raise your blood levels of trimethylamine-N-oxide TMAO over time.

High levels of TMAO are linked to an increased risk of atherosclerosis — a disease that clogs your arteries Doses of 2 g or less per day seem to be well tolerated and safe for most people. However, L-carnitine may increase levels of TMAO, which could be linked to an increased risk of plaque build-up.

You can get small amounts of L-carnitine from your diet by eating meat and dairy products The best sources of L-carnitine are 35 :. As noted before, your body can also produce this substance naturally from the amino acids methionine and lysine if your stores are low. For these reasons, L-carnitine supplements are only necessary in special cases, such as disease treatment.

The main dietary sources of L-carnitine are meat and some other animal products, such as milk. A healthy individual can also produce sufficient amounts within the body.

For this reason, L-carnitine levels are often lower in vegetarians and vegans since they restrict or avoid animal products Therefore, vegetarians and vegans may want to consider L-carnitine supplements, which can help normalize carnitine levels in the blood and muscles In fact, one study found that taking 1.

On the other hand, another study showed that L-carnitine supplementation had no effect on muscle strength or markers of inflammation in older women The risk of deficiency is also higher for those with diseases like cirrhosis and kidney disease.

If you have one of these conditions, a supplement may be beneficial 40 , Specific populations may benefit from L-carnitine supplements. Notably, L-carnitine tartrate prevented the systemic rise in serum ACE2 without affecting ACE1. Previous research has suggested that an imbalance in the action of ACE1 and ACE2 is a primary driver of COVID pathophysiology.

The ability of L-carnitine tartrate to reduce ACE2 is complex; however, our data suggest that it is related, at least in part, to its antioxidant and anti-inflammatory properties. In the rodent study, L-carnitine tartrate supplementation led to a significant increase in the antioxidant capacity, as demonstrated by an increase in superoxide dismutase SOD along with a decrease in inflammation Oxidative stress is defined as an imbalance between the production of reactive oxygen species ROS and levels of antioxidants such as SOD Figure 3.

Infection by SARS-CoV-2 or other viruses has been shown to substantially increase production of free radicals by the immune cells leading to oxidative stress. Similarly, exercise elevates metabolism, causing an increase in the use of oxygen and eventually resulting in oxidative stress 16 , Exercise-induced oxidative stress is known to alter cell structure and function, thereby contributing to inflammation and muscle damage Our rodent trial found that L-carnitine tartrate supplementation lowered oxidative stress, as indicated by a dose-dependent decrease in serum malondialdehyde 15 and, consequently, inflammation.

These changes were paralleled by elevated antioxidant capacity, as shown by increases in several antioxidant enzymes including SOD, catalase and glutathione peroxidase. Collectively, these findings point to a correlation between the effects of L-carnitine on mitigating oxidative stress and inflammation and its effects on lowering ACE2, TMPRSS2 and furin; this suggests a mechanism for the observed effects of L-carnitine on inhibiting the infection of Calu-3 human lung epithelial cells 5.

Moreover, the fact that L-carnitine tartrate led to a decrease in the mRNA levels of ACE2 suggested that it may play a modulatory role through gene-level effects.

This is notable given a recent report that L-carnitine can bind some of the transcription factors, leading to the modulation of their downstream genes such as ACE2 ref.

Figure 3. L-carnitine and oxidative and inflammatory status. L-carnitine helps regulate the balance between oxidative stress and antioxidant capacity in healthy cells. Lower L-carnitine levels may disrupt the balance and increase susceptibility to infections by viruses such as SARS-CoV-2 in inflamed cells.

Immune responses, clinical presentations and severity of outcomes vary notably among patients infected by COVID, and include muscle weakness, fever and respiratory complications. Under extreme scenarios, patients experience a cytokine storm that targets the lungs 3.

Extensive lung transcriptome analysis established that individuals with high risk factors for severe disease outcomes expressed ACE2 at much greater levels than control subjects These findings led Lonza to explore whether L-carnitine tartrate could modulate the expression levels of ACE2 in cultured Calu-3 cells, thereby moderating SARS-CoV-2 infectivity 5.

The results indicated that L-carnitine tartrate reduced ACE2 mRNA levels and dose-dependently decreased SARS-CoV-2 infection in Calu-3 cells 5. Taken together, these findings demonstrate that L-carnitine tartrate treatment significantly decreases the susceptibility of Calu-3 cells to SARS-CoV-2 infection.

These effects are probably mediated through a decrease in the expression of the host factors required by the virus to attach to and enter the cell Figure 4.

Figure 4. L-carnitine and lung-cell infection. L-carnitine reduces levels of ACE2, TMPRSS2 and furin in exercise-induced inflammation models in rats and humans, thereby decreasing susceptibility to SARS-CoV-2 infection.

Oxidative stress induced by acute viral infection helps to stimulate an increased inflammatory response. With the current pandemic, COVID is a primary research target, and scientists and physicians are investigating a wide array of intervention strategies including the use of methods for blunting the inflammatory states that are characteristic of the virus.

Medical presentations of COVID include fever, dry cough and respiratory complications. These symptoms can escalate to life-threatening difficulties for individuals with comorbidities such as type II diabetes, frailty, heart disease and general aging.

A unifying theme connecting these comorbidities is chronic inflammation and low endogenous L-carnitine levels.

Lonza has shown that this nutritional ingredient can blunt systemic exercise-induced inflammation and oxidative stress in both humans and rodents.

Supplementation reduced serum and tissue levels of ACE2, furin and TMPRSS2, which are considered host factors for SARS-CoV-2 entry into human cells. Reduction in expression levels of host factors was correlated with reduced virus infectivity of human epithelial lung cells in a cell-culture model.

Lonza has established the safety and tolerability profile of L-carnitine tartrate in humans at a daily dose of up to 3 g equivalent to 2 g elemental L-carnitine. Future investigations of the effects of L-carnitine tartrate in preventing SARS-CoV-2 infection and complications in human clinical trials are now warranted.

Shane E. Durkee 1 , Zainulabedin M. Saiyed 2 and Aouatef Bellamine 3. Thangasamy, T. et al. Biogerontology 10 , — Article PubMed Google Scholar. Acta , 19—24 World Health Organization. Bruls, Y. EBioMedicine 49 , — Bellamine, A. Nutrients 13 , Abd-Allah, A. Mast, J.

Adeva-Andany, M. IUBMB Life 69 , — Flanagan, J. Article Google Scholar. Bestle, D. Life Sci. Alliance 3 , 1—14 Sriram, K. Phillips, T. Sports Exerc.

Gomes-Santos, I. PLoS One 9, e Emilsson, V. Sahin, K. Nutrients 12 , Fathizadeh, H. Diabetes Metab. Suzuki, K. Antioxidants Basel 9 , Förster, L. Pinto, B. Download references. Skip to main content Thank you for visiting nature. L-carnitine tartrate supplementation in the fight against infectious disease.

Download PDF. Produced by. L-carnitine in immune function Inflammation is an essential part of the immune response to injury and infection 1 , 2. Inflammation-centric COVID COVID is caused by the severe acute respiratory syndrome coronavirus 2 SARS-CoV L-carnitine as an immunomodulator through anti-inflammatory effects Lonza hypothesized that L-carnitine tartrate supplementation may impact ACE2 expression and, consequently, its attachment to the SARS-CoV-2 spike protein through lowering inflammation.

Effects of L-carnitine on host-dependency factors and inflammatory markers during exercise-induced inflammation Our initial study explored the dose-dependent response of L-carnitine tartrate at the tissue level, to determine whether it altered protein and mRNA levels of the host-dependency factors of SARS-CoV-2 infection, ACE1, ACE2, TMPRSS2 and furin, and the inflammatory markers serum CRP and interleukin-6 IL L-carnitine tartrate decreases SARS-CoV-2 infection of Calu-3 cells by downregulating ACE2 receptor expression Immune responses, clinical presentations and severity of outcomes vary notably among patients infected by COVID, and include muscle weakness, fever and respiratory complications.

Conclusions Oxidative stress induced by acute viral infection helps to stimulate an increased inflammatory response.

Doses of 2 g or less per day seem to be well tolerated and safe for most people. However, L-carnitine may increase levels of TMAO, which could be linked to an increased risk of plaque build-up. You can get small amounts of L-carnitine from your diet by eating meat and dairy products The best sources of L-carnitine are 35 :.

As noted before, your body can also produce this substance naturally from the amino acids methionine and lysine if your stores are low. For these reasons, L-carnitine supplements are only necessary in special cases, such as disease treatment.

The main dietary sources of L-carnitine are meat and some other animal products, such as milk. A healthy individual can also produce sufficient amounts within the body. For this reason, L-carnitine levels are often lower in vegetarians and vegans since they restrict or avoid animal products Therefore, vegetarians and vegans may want to consider L-carnitine supplements, which can help normalize carnitine levels in the blood and muscles In fact, one study found that taking 1.

On the other hand, another study showed that L-carnitine supplementation had no effect on muscle strength or markers of inflammation in older women The risk of deficiency is also higher for those with diseases like cirrhosis and kidney disease.

If you have one of these conditions, a supplement may be beneficial 40 , Specific populations may benefit from L-carnitine supplements. This includes older adults and people who rarely or never eat meat.

Although dosage varies from study to study, here is an overview of the use and dose for each form 13 , 19 , 33 :. Although the recommended dose varies, around —4, mg 0. Studies also support its use for health, brain function, and disease prevention.

Supplements may also benefit those with lower levels, such as older adults, vegans, and vegetarians. Of the different forms, acetyl-L-carnitine and L-carnitine are the most popular and seem to be the most effective.

Our experts continually monitor the health and wellness space, and we update our articles when new information becomes available.

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Medically reviewed by Amy Richter, RD , Nutrition — By Rudy Mawer, MSc, CISSN and Rachael Ajmera, MS, RD — Updated on May 9, What it is Weight loss Brain health Other benefits Side effects Food sources Worth taking?

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Dosage recommendations. The bottom line. Similarly, acetyl-L-carnitine supplements improved scores on the Mini Mental State Examination at 24 weeks but not at 12 or 52 weeks and had no effect on the severity of dementia, functional ability, or overall clinical global impression scores.

The authors of the Cochrane Review noted that results from studies conducted more recently were less positive than those from earlier studies; they concluded that the routine clinical use of acetyl-L-carnitine supplements to treat the signs and symptoms of dementia was not justified.

Carnitine plays a role in transporting long-chain fatty acids in the myocardial mitochondria, where they are metabolized via oxidation for energy. It is also involved in moderating oxidative stress [ 33 , 34 ] and might decrease markers of inflammation [ 35 ].

During ischemic events, carnitine prevents fatty acid ester accumulation, which can lead to fatal ventricular arrhythmias [ 34 ]. For these reasons, researchers are examining whether carnitine affects cardiovascular health.

Clinical trials examining the effects of carnitine supplements on CVD have had mixed results. A meta-analysis of 13 clinical trials included a total of 3, adults with acute myocardial infarction who took either L-carnitine from 2.

The study found that L-carnitine significantly reduced rates of all-cause mortality, ventricular arrhythmias, and new-onset angina but did not affect risk of heart failure or myocardial reinfarction [ 34 , 36 ].

The carnitine dose and duration of the clinical trial did not appear to affect outcomes. These benefits did not vary by supplement dose or study duration. However, L-carnitine did not affect rates of all-cause mortality or performance on a timed walking test.

Other research has raised concerns about the negative cardiovascular effects of chronic exposure to carnitine. A study that included 2, adults age 54—71 years undergoing elective cardiac evaluation found that L-carnitine is metabolized by intestinal microbiota to trimethylamine-N-oxide TMAO , a proatherogenic substance that is associated with increased CVD risk [ 38 ].

Because of differences in intestinal bacteria composition, omnivorous study participants produced more TMAO than vegans or vegetarians after consumption of L-carnitine. The study also found dose-dependent associations between fasting plasma L-carnitine concentrations and risk of coronary artery disease, peripheral artery disease, and CVD, but only in participants with concurrently high TMAO levels.

A clinical trial also found potentially deleterious outcomes in individuals age 58 to 75 years with metabolic syndrome who received 1 g supplemental L-carnitine or placebo twice a day for 6 months [ 39 ].

Although the results showed no differences in total plaque volume between groups, total cholesterol and low-density lipoprotein cholesterol levels were higher in participants taking L-carnitine. L-carnitine supplementation was also associated with 9.

Peripheral artery disease is a vascular disorder usually caused by atherosclerosis and its resulting arterial stenosis and occlusion. It is prevalent among older adults, although it is often underdiagnosed [ 40 , 41 ].

Researchers have examined whether propionyl-L-carnitine, an acyl derivative of L-carnitine, mitigates the cramping leg pain of intermittent claudication, the main symptom of peripheral artery disease, but findings from studies have been mixed.

In one trial, participants supplemented with propionyl-L-carnitine had improved peak walking times walking until pain could not be tolerated , self-reported improvements in walking distance and speed, and decreased pain.

The other two trials showed no benefit of propionyl-L-carnitine on peak walking time compared with placebo. Insulin resistance plays an important role in the development of type 2 diabetes. Because insulin resistance may be associated with mitochondrial dysfunction and a defect in fatty-acid oxidation in muscle [ 43 , 44 , 45 , 46 ], carnitine supplementation has been studied for its possible effects on insulin resistance and diabetes.

A meta-analysis of 41 randomized clinical trials examined the effects of L-carnitine supplementation on glycemic markers in 2, men and women age 18 years and older [ 47 ]. Most participants had health conditions such as type 2 diabetes, obesity, polycystic ovary syndrome, or nonalcoholic fatty liver disease.

L-carnitine supplements at doses of 0. Other meta-analyses have had a narrower focus, examining only studies in specific populations. The L-carnitine improved measures of insulin resistance, and the benefits at 12 months exceeded those at 3 months. A systematic review and meta-analysis of four randomized clinical trials all of which were included in the meta-analysis described above with a total of adults with type 2 diabetes compared the metabolic effects of L-carnitine with those of placebo [ 44 ].

Additional clinical trials with larger samples are needed to determine whether L-carnitine supplements can reduce the risk of diabetes or the severity of its clinical manifestations. Carnitine might play a role in sperm maturation, sperm motility, and spermatogenesis [ 49 ].

It might also reduce oxidative stress, which could improve oocyte growth and maturation [ 50 ]. Therefore, researchers are examining whether supplemental carnitine improves sperm count, concentration, and motility as well as pregnancy rates.

Compared to placebo, supplemental carnitine improved sperm motility by 7. A Cochrane Review assessed the effectiveness of carnitine supplementation on male subfertility delays in conception due to low sperm concentration [ 52 ].

In some trials, carnitine was compared with placebo, whereas in others, it was compared with antioxidants such as vitamin C or vitamin E or a control group that received no treatment. Carnitine supplementation increased sperm motility and concentration at some timepoints e. Researchers have also examined whether carnitine might improve ovulation and pregnancy rates in females with polycystic ovary syndrome PCOS , a condition that commonly causes infertility.

Individuals in the group taking L-carnitine had In addition, more participants in the L-carnitine group became pregnant than those who took placebo, and they had fewer miscarriages. In a 3-month randomized controlled trial, women with PCOS received either 3 g L-carnitine or placebo [ 54 , 55 ].

Participants who took L-carnitine supplements had improved menstrual cycle regularity and higher ovulation and pregnancy rates, but miscarriage rates did not differ between the groups.

More research is needed to determine whether carnitine supplements affect male infertility or pregnancy rates in women with PCOS. Some research suggests that carnitine reduces levels of C-reactive protein, a biomarker of systemic inflammation, and levels of malondialdehyde, a lipid peroxidation product that induces pain and disability in patients with osteoarthritis [ 56 ].

In addition, levels of acylcarnitines conjugated carnitine esters are lower in people with osteoarthritis than in age- and gender-matched healthy individuals [ 57 ].

For these reasons, investigators are studying whether L-carnitine supplements can relieve osteoarthritis symptoms [ 56 , 58 ], but study results have been mixed. A randomized clinical trial examined the anti-inflammatory effects of L-carnitine supplementation for osteoarthritis management in 69 women age 40 to 60 years with mild to moderate osteoarthritis in both knees [ 59 ].

The women took mg L-carnitine three times a day or placebo for 8 weeks. Serum levels of several inflammation biomarkers and pain scores were lower in the carnitine group than in the placebo group: Interleukinbeta levels decreased 5. In comparison with placebo, carnitine did not reduce osteoarthritis pain or stiffness or increase physical function.

Larger studies with samples that include both men and women are needed to determine whether carnitine supplementation helps manage osteoarthritis symptoms. Carnitine helps preserve muscle glycogen and promote fat oxidation. It also spares the use of amino acids as energy sources during exercise, making them potentially available for new protein synthesis [ 6 ], and decreases the accumulation of lactate [ 60 ].

However, research findings on the effectiveness of supplemental carnitine on athletic performance are mixed [ 6 ]. One study randomly assigned 14 recreational athletes age 24—28 years with an average body mass index BMI of 23 to consume a carbohydrate solution with or without 2. In another study, 24 men age 18—40 years eight omnivores and 16 vegetarians took 1 g L-carnitine twice daily for 12 weeks [ 62 ].

Carnitine supplementation had no significant effect on VO2max, blood lactate concentration, skeletal muscle energy metabolism, or physical performance in either the vegetarians or the omnivores. A comprehensive review summarized the effects of supplemental L-carnitine on exercise performance and recovery in well-trained athletes age 16—36 years and recreationally active adults age 18—50 years [ 63 ].

The review included 11 clinical trials one of which was the trial described above in a total of well-trained athletes who took 1 to 4 grams L-carnitine or placebo a single time or once or twice daily for up to 6 months.

L-carnitine supplements reduced lactate levels and heart rate; increased lipid metabolism, VO2max, oxygen consumption, and L-carnitine plasma concentrations; improved performance; and hastened recovery in some of the studies.

However, the supplements did not affect performance or maximal exercise test results in other studies. In 17 studies that included recreationally active adults, a total of participants took 2 g L-carnitine once or 2 to 4 g L-carnitine or placebo once or twice daily for up to 3 months.

L-carnitine decreased plasma lactate concentrations, pyruvate concentrations, and muscle soreness and increased VO2max and recovery in some studies. However, in other studies, L-carnitine did not affect lactate, heart rate, VO2max, endurance, performance time, or perceived exertion during exercise.

A systematic review of 11 randomized clinical trials examined the effects of oral L-carnitine supplementation on high- and moderate-intensity exercise performance in a total of physically active and untrained adults age 18 to 46 years [ 64 ].

The studies had mixed results. Some studies found significant improvements in VO2max, peak power, maximum sprinting power, perceived exertion, and number of repetitions and volume lifted in a leg press in the L-carnitine group.

However, other studies found no differences in VO2max, fatigue, maximum and average power, or total work on a cycle ergometer. No studies found that L-carnitine supplementation improved moderate-intensity exercise performance.

Because carnitine transports fatty acids into the mitochondria and acts as a cofactor for fatty acid oxidation, researchers have proposed using L-carnitine supplements to promote weight loss, often in conjunction with a low-calorie diet, exercise, or prescription weight-loss drugs [ 65 ].

Weight loss has been a secondary outcome in most studies, and these studies have had equivocal results. The trials included a total of participants. In eight trials, doses ranged from 1.