L-Carnitine: Benefits, side-effects, uses, dosage and research

What is carnitine?

L-carnitine is a chemical present in almost all cells of the body. Derived from the Latin word carnus, which means flesh. Carnitine is a compound isolated from meat and is present in the following forms: 

  • Acetyl-L-carnitine 
  • Propionyl-L-carnitine 
  • L-carnitine 

L-carnitine is made from the amino acids methionine and lysine and is needed to release energy from lipids or fats. 

The role of carnitine in energy production

Carnitine plays an essential role in the production of energy in the body. It transports long-chain fatty acids into the cell’s mitochondria. These long-chain fatty acids are then oxidized to produce energy.

Apart from facilitating the entry of long-chain fatty acids, it also transports toxic compounds out of the mitochondria. Transporting toxic compounds out of the mitochondria will help prevent their accumulation in these organelles. 

The heart and the skeletal muscles are examples of organs with a high density of mitochondria. These organs require vast energy and use fatty acids to generate energy [1]. 

Most people produce carnitine naturally. However, carnitine is not produced sufficiently for some, such as infants or people with medical and genetic problems, leading to muscle weakness, clumsiness, vomiting and confusion.

Hence, carnitine is considered an essential nutrient, so supplementation with this nutrient is necessary to meet the body’s demands. 

What foods are rich in carnitine?

Red meat contains the highest amount of carnitine, but you can find significant amounts in fish, poultry, milk and other animal products. Small amounts of carnitine are also found in dairy products like cheese, ice cream, whole wheat bread and asparagus.

Amongst the three forms of carnitine, L-carnitine is the only active form of the nutrient in the body.

What are the benefits of carnitine? 

Carnitine is essential because, without it, one’s body wouldn’t be able to produce energy well. Other benefits of L-carnitine based on studies published in the past years include:

1. Antioxidant properties

Due to its antioxidant properties, carnitine is currently proposed to treat several conditions. Antioxidants are compounds naturally found in the body that fight harmful substances called free radicals. These free radicals are produced during metabolism and the production of energy.

Usually, the body has sufficient antioxidants to counter the number of free radicals present. However, when there are too many free radicals, this can lead to aging or early destruction of cells in the body. 

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What are the benefits of Carnitine? 

2. Secondary prevention of cardiovascular disease 

A systematic review [1] published in the Mayo Clinic Proceedings journal evaluated the effects of L-carnitine on reducing morbidity and mortality from acute myocardial infarction.

Investigators of the study, led by James DiNicolantonio from Wegmans Pharmacy in Ithaca, New York, only included randomized controlled trials that compared the effects of L-carnitine against a placebo.

A total of 13 controlled trials were reviewed and a meta-analysis was done. A total of 3,629 patients were included in all the trials. 

Results of the review showed that patients who received L-carnitine supplementation and experienced an acute heart attack had a 27% reduction in all-cause mortality from cardiovascular disease compared with the control group.

Patients who received carnitine had a significant 65% reduction in ventricular arrhythmias. They also have a significant 40% reduction in developing angina symptoms while suffering from an acute myocardial infarction. 

Results from this study provide essential baseline information that supplementation with L-carnitine, an inexpensive therapy, could reduce mortality risk following myocardial infarction.

Further, L-carnitine supplementation can help prevent the development of ventricular arrhythmias or angina symptoms during an acute heart attack. 

However, the study’s authors recommend that more extensive, randomized controlled trials be needed to confirm the systematic review’s findings. 

3. Prevention of muscle wasting 

Muscle wasting is muscle atrophy and is common among older adults. This condition is marked by reduced skeletal muscle mass and adipose tissues.

Since the skeletal muscles are crucial in body metabolism and movement, muscle wasting can lead to poor quality of life and poor prognosis in patients admitted to hospital settings. Hence, it is crucial to combat this condition through proper treatment. 

L-carnitine, an antioxidant, has been shown to delay muscle wasting or prevent this condition from happening. According to one research [2], oxidative stress has been associated with muscle wasting.

When the antioxidant ability of a cell is reduced, this can lead to the generation of superoxide radicals (ROS-like) and peroxynitrite. Once these are present, they can damage lipids, proteins and even DNA. Patients with muscle loss have high levels of ROS in their blood. 

Animal and human studies have shown that supplementation with L-carnitine improved protein synthesis, prevented cell death, decreased protein breakdown and reduced inflammatory responses of the cells [3]. As a result, this reduces muscle wasting among older adults and those who are chronically ill. 

4. Delay progression of Alzheimer’s Disease 

Alzheimer’s Disease (AD) is marked by significant and progressive cognitive impairment and memory loss. Although this condition is prevalent among older adults, younger people can have early-onset dementia or Alzheimer’s Disease. 

There is evidence that supplementation with L-carnitine might delay the progression of AD. Although the results of earlier systematic reviews and randomized controlled trials were mixed, there is now recent evidence that supplementation with L-carnitine and a balanced diet might prevent dementia [4]. 

5. Has potential to treat chronic heart failure

Chronic heart failure affects at least 26 million people in the world. This condition is characterized by hemodynamic abnormality, decreased contractility and neuroendocrine activation. It remains the leading cause of death and morbidity worldwide. 

Currently, the treatment for heart failure includes the following: 

  • Angiotensin receptor blockers 
  • ACE inhibitors 
  • Beta-blockers 
  • Mineralocorticoid receptor antagonists 

Recently, there has been a focus on L-carnitine as a nutrient that might benefit heart failure. L-carnitine is composed of amino acids and plays a critical role in the body’s metabolic activities. In high concentrations, there is growing evidence that L-carnitine can help treat congestive heart failure, coronary artery disease and peripheral vascular disease [5]. 

Researchers [6] from the Department of Cardiology at Shuguang Hospital in Shanghai, China, conducted a systematic review of randomized controlled trials that investigated the beneficial effects of L-carnitine on chronic heart failure. 

A total of 17 randomized controlled trials (RCTs) that included a total of 1625 CHF patients were included in the review and meta-analysis. Findings were pooled to examine if L-carnitine supplementation improves CHF outcomes. 

L-Carnitine and Chronic heart failure 

The study’s findings showed significant improvements in cardiac output, left ventricular ejection fraction and stroke volume following L-carnitine treatment. All these improvements signify an improvement in the heart’s function. 

Further, the study authors also found that brain natriuretic peptide (BNP), a cardiac neurohormone biomarker, significantly reduced after intake of an L-carnitine supplement.

Healthcare practitioners rely on BNP levels when determining if patients in the emergency department are at high risk for cardiac events. The BNP levels are used in emergency hospital settings to diagnose heart failure. The BNP hormone is released from the ventricles when the latter is under increased stress and pressure. 

Patients enrolled in the randomized controlled trials were taking 1.5 grams to 6 grams of L-carnitine daily. Currently, 500 to 2000 mg of L-carnitine is recommended in healthcare settings.

In the systematic review, the 6000 mg of L-carnitine daily did not lead to toxicity or adverse effects. This suggested that doses as high as 6000 mg per day are still well tolerated in patients with chronic heart failure. 

However, the authors of the systematic review admitted that the L-carnitine supplementation duration differed in the studies. Further, follow-up periods in the studies were different. Patients were followed up for seven days to 3 years.

Considering the heterogeneity of the duration of the supplementation, it is difficult to determine the appropriate number of weeks or months that a patient with chronic heart failure should receive L-carnitine to experience positive health outcomes. 

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6. May improve brain function 

There is evidence that L-carnitine may improve brain function. 

The acetyl-L-carnitine form has been shown to reverse cognitive decline in patients with brain disease and Alzheimer’s. In older adults, brain function improves with L-carnitine supplementation [7]. 

In another study [8], chronic alcoholic patients treated with acetyl-L-carnitine at 2000 mg daily demonstrated significant improvements in brain function following treatment. 

7. Boosts exercise performance 

Although studies on L-carnitine and its effects on exercise performance have mixed results, some studies suggest that L-carnitine given for more extended periods and in larger doses results in improved exercise performance. 

Reaping the benefits of L-carnitine, however, take time. Recent studies demonstrate that the effects often take time to be seen. Some results are seen only after weeks or months of taking the supplement. 

An older study [9] indicated that taking 3000 mg daily of L-carnitine for seven weeks reduced muscle pain. The study, published in the International Journal of Sports Medicine, also reported that muscle tenderness and creatinine kinase levels significantly reduced after L-carnitine intake. Creatine kinases are released from damaged muscle cells. 

The findings of this study provided evidence that L-carnitine might help improve the physical functioning of the skeletal muscle cells and promote recovery after exercise. 

There is also evidence that L-carnitine might improve oxygen flow into the muscle cells. This is important as an increased oxygen supply would reduce lactic acid formation. Lactic acid accumulation occurs when insufficient oxygen in the muscle cells to help produce energy. In turn, this results in muscle cramps. 

L-carnitine may also help reduce fatigue since it increases nitric acid production and blood flow to the skeletal muscles during exercise. 

Finally, it is found that L-carnitine may increase the production of red blood cells. These cells transport oxygen to the muscle cells and all the other cells throughout the body. 

8. Improves insulin sensitivity

Type 2 diabetes is a condition marked by hyperglycemia or high blood sugar levels. This disease develops following the destruction of beta cells in the pancreas. Beta cells are responsible for the production of insulin, a hormone that facilitates the entry of glucose into the cells in the body.

This condition is also accompanied by decreased uptake of peripheral insulin, which increases the glucose level in the blood. Type 2 diabetes is a severe condition and when left unmanaged, it can result in complications ranging from diabetic glaucoma to diabetic foot. 

A study [10] led by Stuart Galloway from the Sport, Health and Exercise Sciences Research Group from the University of Stirling in the UK investigated the effects of L-carnitine supplementation on insulin sensitivity amongst overweight or obese males. 

Results of the study, which were published in the Amino Acids journal, demonstrated that supplementation with L-carnitine resulted in a reduction of symptoms of diabetes and improvement in insulin sensitivity amongst overweight and obese males. 

The importance of L-carnitine supplements

As the body ages, the amount of carnitine also reduces, which means less energy to move around as much as you did when you were younger.

Hence, carnitine supplementation may be necessary to ensure appropriate amounts of this nutrient. However, talking to your doctor before taking these supplements would be best. 

Side effects of L-carnitine

L-carnitine given in doses of 2000 mg or 2 grams daily is safe and well tolerated. An amount of 3000 mg or 3 grams per day may still be safe. A study [11] reported that participants taking 3000 mg of L-carnitine supplementation for three weeks showed no adverse effects following supplementation.

Long-term use of L-carnitine supplementation may have some side effects. Even at a 2000 mg dose, prolonged use could result in mild side effects such as stomach discomfort and nausea. 

Side effects of L-carnitine

There is also evidence that long-term use of L-carnitine may raise blood levels of TMAO or trimethylamine-N-oxide over time. High levels of this compound have been linked to an increased risk of atherosclerosis.

Atherosclerosis is a condition where the arteries in the body, especially those supplying the heart, are clogged with lipids or fats. This can increase the risk of heart disease or heart attack. 

Meanwhile, an animal model study [12] published in the Human and Experimental Toxicology journal showed that 8-week supplementation with L-carnitine at 0.3 to 0.6 g/kg reduced body weight, liver, kidney and serum lipid fat levels.

However, the same study also reported that enzymes needed for the proper functioning of the kidneys were disturbed after L-carnitine supplementation. 

Although the study was conducted in laboratory animals, the findings indicated that long-term use of L-carnitine might alter kidney functioning.

There is a need to observe the same results in human studies in the future as L-carnitine might be used to prevent cardiovascular diseases, manage type 2 diabetes and improve brain function in adults. 

What is the recommended dosage for carnitine? 

Healthy adults and infants who eat sufficient meat and other food sources rich in carnitine do not need carnitine supplementation. 

People who do not need supplementation should take at least 500-2000 mg of carnitine from their diet or 0.5 to 2 grams of carnitine daily. 

About a half cup of cooked beef steak (4 ounces) contains 56-162 mg of carnitine, while a whole cup of milk has 8 mg of carnitine. A half cup of cooked ground beef contains 87-99 mg of carnitine. 

If your diet is insufficient to meet your demands for carnitine, you can take carnitine supplements that are available in 500 to 2000 mg dosages. 

The latest research on carnitine 

Prolonged use of L-carnitine can improve mortality 

There have been conflicting results on the effects of prolonged use of L-carnitine on the body. However, there are now more recent studies that suggest that more prolonged use of L-carnitine can indeed improve mortality. 

A study [13] published in the Journal of Personalized Medicine recruited 13,413 subjects to examine if the carnitine-orotate complex can reduce mortality. This study was a population-based study that recruited a nationwide cohort from South Korea.

All individuals enrolled in the study were prescribed the carnitine-orotate complex and underwent a national health examination. Participants in the study were classified into three groups.

The first group used a carnitine-orotate complex for less than 30 days. The second group took the supplement for 30 to 180 days, while the third group took carnitine-orotate complex for more than 180 days. 

After the follow-up period, investigators in the study examined the mortality rate of the three groups. Individuals who took carnitine-orotate complex for more than 180 days had significantly reduced mortality rates compared with those who used the supplement for less than 30 days. 

Interestingly, the study found that those with metabolic risk factors benefited the most from the carnitine-orotate complex. These individuals were at high risk of dyslipidemia, metabolic syndrome, obesity and fatty liver.

For this group of people, taking L-carnitine supplements for more extended periods could help reduce the risk of dying from obesity, fatty liver and other metabolic disorders. 

Further, the study also revealed that older adults benefited from the supplement more than the young people included in the study. It is recognized that older adults are at increased risk of deficient carnitine due to reduced intake of meat and other dairy products or poor nutrition in this age group. Hence, supplementation with L-carnitine can help improve levels of this nutrient in the body. 

L-carnitine supplementation, body composition and weight loss 

It is believed that L-carnitine might help people who are obese or overweight lose weight since this compound ferries long-chain fatty acids into the mitochondria to be metabolized into energy.

However, there are conflicting findings on whether L-carnitine can lead to weight loss. Earlier studies showed mixed results on the efficacy of L-carnitine in promoting weight loss. 

A recent systematic review [14] published in the Clinical Nutrition Espen journal revealed that L-carnitine had a modest but significant effect on weight loss, especially amongst those who are obese and overweight.

To reap the benefits of L-carnitine as a weight-loss supplement, the study authors stated that one should take 2000 mg of the supplement each day. 

Results of the systematic review confirm that a healthy diet and exercise should accompany supplementation with L-carnitine to optimize weight loss in those who are obese or overweight. 

L-carnitine and autism 

Several studies investigating the effects of L-carnitine supplementation on autism have been conducted in the past. 

In a recent narrative review [15], L-carnitine at doses of 50 to 100 mg/kg/day was generally well tolerated when given to individuals with an autism spectrum disorder.

Although the findings were inconclusive, previous studies’ initial results demonstrated that L-carnitine supplementation could reduce the severity of autism spectrum disorder. Notably, there were improvements in muscular strength and a reduced intellectual disability. 

Autism spectrum disorder is characterized by deficits in social interaction and communication and repetitive or restricted patterns of behavior, activities and interests. Although the causes of this disorder are multifactorial, evidence suggests that environmental and genetic factors influence this condition. 

In both non-syndromic and syndromic autism, researchers discovered that carnitine and its derivatives are altered. Hence, it is believed that supplementation with L-carnitine might reduce the severity of the disorder for specific individuals in the autism spectrum. 

L-carnitine and diabetic neuropathy 

L-carnitine might help reduce pain in individuals with diabetic neuropathy. Diabetic neuropathy is one of the complications of type 2 diabetes mellitus.

This condition is characterized by nerve damage due to high blood sugar levels. As a result of this nerve damage, individuals can experience pain and numbness in the legs, arms and feet. 

Previous studies have suggested that L-carnitine might help regenerate the affected nerves, thereby reducing pain and increasing sensation or feelings in affected nerves. 

A recent systematic review [16] suggested that L-carnitine reduces pain levels by 20.2% compared with placebo in patients with diabetic neuropathy.

Further, the same study reported positive effects on nerve fiber regeneration and nerve conduction parameters following supplementation with L-carnitine. 

Patients with painful peripheral neuropathy could benefit from L-carnitine supplementation at doses within safe levels. As demonstrated in the review, doses ranged from 500 to 3000 mg of L-carnitine daily. 

Takeaway 

L-carnitine is an essential nutrient in the body since it helps burn lipids or long-chain fatty acids in the mitochondria. It is also an antioxidant and plays a role in scavenging radicals in the body.

Due to the properties of L-carnitine, it is believed that this can help individuals lose weight. However, the effects of L-carnitine on weight loss are mixed.

In those who did experience weight loss, the weight reduction was significant but modest. However, L-carnitine proves to be promising in treating cardiovascular diseases such as chronic heart failure and preventing myocardial infarction.

It could also improve brain function and reduce the severity of cognitive impairment. L-carnitine might also be beneficial for individuals with an autism spectrum disorder. 

Finally, talking to your doctor when taking this supplement is crucial. Since most individuals have sufficient L-carnitine in their bodies, you might not need this supplement.

However, if you belong to the older age group or have insufficient L-carnitine levels due to genetic and environmental factors, it is necessary to take L-carnitine supplementation. 

Taking the supplement as prescribed and only taking the recommended dosage would ensure optimal health outcomes and safety. 

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[1] https://pubmed.ncbi.nlm.nih.gov/23597877/
[2] https://pubmed.ncbi.nlm.nih.gov/24599831/ 
[3] ​​https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9827390/ 
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7400709/ 
[5] https://pubmed.ncbi.nlm.nih.gov/29241711/
[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5406747/ 
[7] https://pubmed.ncbi.nlm.nih.gov/2201659/ 
[8] https://pubmed.ncbi.nlm.nih.gov/2201652/ 
[9] https://pubmed.ncbi.nlm.nih.gov/8858401/ 
[10] https://pubmed.ncbi.nlm.nih.gov/20963457/#affiliation-1 
[11] https://pubmed.ncbi.nlm.nih.gov/11726261/ 
[12] https://journals.sagepub.com/doi/full/10.1177/0960327115571767 
[13] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9787718/
[14] https://pubmed.ncbi.nlm.nih.gov/32359762/ 
[15] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6930613/
[16] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6498091/ 

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