L-Carnitine: Benefits, Dosage, Side Effects, and More

Along with a couple other closely related compounds, including acetyl-L-carnitine and propionyl-L-carnitine, L-carnitine has become a popular dietary supplement in recent years amongst health and fitness enthusiasts all over the world.  

While it may be becoming more well-known, many still aren’t exactly sure what it is.  That’s why in this article we’re going over everything you need to know about L-carnitine, from what it is and what the benefits are to how to take it safely and effectively.   

What is L-Carnitine?

L-carnitine is a naturally occurring substance derived from the essential amino acids lysine and methionine, although your body also needs an adequate supply of vitamin C in order to synthesize it.⁽¹⁾

It’s present in just about every cell in the human body, however, it’s primarily concentrated in skeletal and heart muscle tissues.

L-carnitine plays an important role in your body’s production of energy, helping to transport long-chain fatty acids to be oxidized in your cells’ mitochondria.⁽²⁾

Also referred to as the powerhouse of a cell, the mitochondria is primarily responsible for breaking down nutrients into molecules that can be used by your cells as energy.  

On top of that, L-carnitine also ferries unwanted byproducts out of the mitochondria, helping to prevent the buildup of toxic compounds that can hinder operations.⁽³⁾

Sources of L-Carnitine

Food Sources

L-carnitine can be obtained from a variety of different dietary sources, however, it’s mostly found in animal-based foods.  Common foods that contain L-carnitine include:

*All Information obtained from the NIH’sHealth Professional Fact Sheet

Supplements

In addition to being found in certain types of foods, L-carnitine is also available as a dietary supplement, with a number of different products currently available here in the U.S. 

L-carnitine supplementation may be particularly advantageous to those on plant-based diets, as L-carnitine is mostly only found in animal products and a deficiency can lead to several adverse health outcomes.  

L-Carnitine Benefits

Because of the central role it plays in cellular energy production, L-carnitine has received a considerable amount of attention amongst medical and nutritional scientists.  As such, a variety of clinical and experimental studies have investigated the effects of L-carnitine supplementation on a range of different issues.  

To date, several benefits have been associated with L-carnitine supplementation, however, while a few of these benefits appear to be well supported by the research, more trials need to be conducted before we can say anything for sure when it comes to others.

Cognition

There is a considerable amount of evidence that L-carnitine supplementation may help to improve several aspects of cognition, which is why it’s sometimes referred to as a nootropic substance.  From memory recall to mental processing, numerous animal and human studies have found that L-carnitine had a positive effect on cognitive performance.⁽⁴⁾⁽⁵⁾

However, most research investigating the effects of L-carnitine on brain function has involved individuals with cognitive impairments.  Few if any studies have involved healthy, young adults.   

With that being said, a 2010 double-blind, placebo-controlled study published in Metabolic Brain Disease examined the effects of (acetyl-)L-carnitine supplementation on brain function in individuals with liver-related brain damage.⁽⁶⁾

61 participants were split up into one of two groups and given a series of assessment tests evaluating several aspects of their cognition.  Group 1 received an L-carnitine supplement twice a day for 90 days, while the other group was given only a placebo. 

At the conclusion of the trail, the researchers ultimately found that in comparison to the placebo group, those who were given L-carnitine, on average, demonstrated significantly greater improvements in everyday and logical memory.  

On top of liver-related brain damage, research has also demonstrated positive effects on cognition in elderly folks with age-related cognitive decline --the aging process is associated with the slow decline of brain function (along with several other physiological functions).  

For example, a 2007 double-blind, placebo-controlled study published in The American Journal of Clinical Nutrition recruited seventy 100+-year-old individuals to investigate the effects of L-carnitine on age-related cognitive decline.⁽⁷⁾

Subjects were placed in one of two groups, with group 1 receiving an L-carnitine supplement once a day for 60 days, while group 2 receiving only a placebo. At the end of the study, participants who received a daily dose of L-carnitine, on average, demonstrated significantly better improvements on a cognitive assessment test in comparison to the placebo group.  

While the findings seem promising when it comes to L-carnitine supplementation and cognitive impairment, more research needs to be done before we can say for sure whether or not the same effects can be observed in younger individuals with normal brain function.  

Mental and Physical Fatigue

In addition to reversing cognitive decline, some research also shows that L-carnitine supplementation may help to reduce both mental and physical fatigue as well.⁽⁸⁾

For instance, using a standardized fatigue severity scale, a 2008 study published in the Archives of Gerontology and Geriatrics explored the effects of (acetyl-)L-carnitine supplementation on elderly patients with chronic fatigue syndrome.⁽⁹⁾

The researchers gave study participants either a daily L-carnitine supplement or a placebo.  At the conclusion of the trial, those who were given L-carnitine, on average, demonstrated significant reductions in both mental and physical fatigue as well as improvements in functional status. 

While several studies on elderly patients have indeed demonstrated positive findings, there aren’t any direct studies on younger adults, making it more difficult to evaluate the efficacy of L-carnitine supplementation for treating fatigue in broader populations.  

Exercise Performance

Some research also suggests that L-carnitine supplementation may help to improve exercise performance. For example, a 2004 systematic review published in Nutrition evaluated over 20 different studies involving L-carnitine supplementation in athletes.⁽¹⁰⁾

 The majority of studies included in the review ultimately found that those who were given a daily dose of L-carnitine, on average, saw significant improvements in exercise performance.  

More specifically, several studies found that L-carnitine supplementation helped to improve maximum oxygen consumption (VO2max) in athletes during high-intensity exercise, allowing them to work at higher intensities for longer periods of time.^(11)(12)(13)

In addition to improving athletes’ VO2max during high-intensity exercise, several studies have also found that L-carnitine supplementation helped to improve exercise performance by decreasing the build-up of lactic acid in athletes’ muscles.⁽¹⁴⁾

While most research to date has demonstrated significant results, the finds are still mixed.  A small number of studies did fail to find any effects of L-carnitine on exercise performance at all, although this may be due too the designs of the studies.^(15)(16)

Muscle Recovery Post-Workout

On top of improving the performance of your muscles while you exercise, some research also shows that L-carnitine supplementation may help to improve their recovery afterward. 

More specifically, several studies have demonstrated that taking a daily dose of L-carnitine helped to prevent muscle protein breakdown (MPB) post-workout -- exercise causes muscle damage, which can lead to pain and soreness in the hours and even days following a workout.^(17)(18)

For example, a 2003 placebo-controlled cross-over study published in the Journal of Strength and Conditioning Research ultimately found that compared to the placebo group, those who were given L-carnitine, on average, saw significant increases in the production of anabolic hormones like testosterone and insulin-like growth factor post-workout.  

The researchers found that this, in turn, helped to significantly reduce the amount exercise-induced muscle damage participants experienced -- muscle tissue damage was assessed using magnetic resonance imaging scans.⁽¹⁹⁾

Cardiovascular Disease

There’s also a sizeable body of evidence that L-carnitine supplementation may help to prevent heart disease and cardiovascular-related mortality.  

For example, a 2013 systematic review that evaluated 13 different placebo-controlled trials investigating the effects of  L-carnitine supplementation on heart health, ultimately found that L-carnitine was associated with significant reductions in mortality (27%), ventricular arrhythmias (65%), and angina (40%).⁽²⁰⁾

There is also some evidence that daily L-carnitine supplementation may help to reduce arterial hypertension as well.  A 2009 study published in Hypertension demonstrated that subjects who were given a daily L-carnitine supplement saw significant reductions in systolic blood pressure -- high systolic blood pressure is associated with an increased risk of heart disease.  ⁽²¹⁾

Type 2 Diabetes

Those with type 2 diabetes may also see some benefits from supplementing with L-carnitine.  For instance, a 1999 study published in the American Journal of the College of Nutrition found that L-carnitine supplementation significantly improved glucose uptake in patients with type 2 diabetes.⁽²²⁾

In addition, other research also suggests that L-carnitine supplementation may help to reduce pain and improve nerve regeneration in patients with Chronic Diabetic Neuropathy (CDN) as well.⁽²³⁾

Weight Loss and L-carnitine

While there have been a number of claims that L-carnitine supplementation helps to promote weight loss, these assertions don’t appear to be well-supported by scientific evidence. 

For example, a 2016 systematic review investigating the effects of L-carnitine supplementation on weight loss evaluated the findings in 9 randomized, controlled trials.  The researchers ultimately found that while some studies demonstrate changes in participants’ weight, the effects of L-carnitine on weight loss were not statistically significant.⁽²⁴⁾

So, while minimal effects may exist, the current findings don’t appear to support the notion that L-carnitine is an effective tool for weight loss.  Instead, a well-balanced, hypocaloric diet is far more effective when it comes to losing weight.  

L-Carnitine Side Effects and Safety

L-carnitine is considered to be a generally safe dietary substance and research shows that it well-tolerated in humans, posing no serious long or short term risks to your health at appropriate dosages.⁽²⁵⁾

As far as side effects go, nausea, abdominal cramping, diarrhea, and vomiting have all been reported when L-carnitine was consumed in excess.⁽²⁶⁾

L-carnitine may also cause unwanted interactions with anticonvulsant medications, so you’ll certainly need to consult with your doctor if you’re on medication like phenobarbital before you begin taking L-carnitine.

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Dosage Recommendations

A standardized recommended dietary allowance (RDA) has not yet been established for L-carnitine.⁽²⁷⁾ However, most studies administered somewhere between 1 to 3 grams of L-carnitine per day, with little to no adverse effects reported.  The risk of side effects appears to increase when daily intake exceeds 3 grams per day.

Wrap Up

L-carnitine is a dietary substance that plays a critical role in cellular energy production and researchers have associated several potential benefits with daily supplementation.  

While there doesn’t appear to be a whole lot of evidence that it’s effective for weight loss, there is substantially more proof that it may offer certain benefits when it comes to brain health, exercise performance, and heart health.   

Although research seems promising when it comes to L-carnitine supplementation, most trials have focused on older folks and or those with chronic conditions.  While research shows that it’s generally safe and well-tolerated in humans, more research needs to be done before we can say for sure if certain benefits can be observed in healthy young and middle-aged adults. 

• References
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