L-Carnitine: Much More Than a Gym Supplement

Carnitine is an amino acid derivative from the essential amino acids lysine and methionine. Its key role in intermediary metabolism is the transport of long-chain fatty acids from the cytosol to the mitochondrial matrix. That’s where fatty acid β-oxidation occurs, the process of releasing energy is from fats.

Carnitine occurs in two forms (D and L) that are mirror images (isomers) of each other but only L-carnitine is the active form. L-carnitine is obtained primarily from red meat and dairy products but can also be found in a highly pure form as a dietary and fitness supplement. Carnitine is also synthesized in the kidney, liver and brain.

Conversely, it’s considered a “quasi-vitamin” or “conditionally essential” micronutrient. Under certain circumstances (in premature infants, elderly patients, diabetes and genetic conditions resulting in primary or secondary carnitine deficiency) maintaining a healthy diet might not be enough to keep carnitine levels in physiological values.

Other functions include preservation of cell membrane integrity, stabilization of a physiologic coenzyme A (CoASH)/acetyl-CoA ratio in mitochondria and managing the body’s acidity through the reduction of lactate production.

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What Does L-Carnitine Do For You?

L-Carnitine appears to be the one that chooses the fuel for exercise. During low-intensity exercises, fatty acid oxidation is favoured as a source of energy. The utilization of energy from fat increases endurance, spares muscle glycogen and delays the onset of fatigue. At a moderate intensity of work, both glucose and fatty acids may be used, with a gradual increase in glucose over fat consumption as the intensity increases.

Glycogen represents a major source for ATP (the energy currency of the body) regeneration during prolonged exercise (>1 h) and high-intensity intermittent exercise. When glycogen stores are limited, exercise cannot continue. Glycogen is rapidly depleted under high-intensity endurance exercise due to its limited storage, resulting in fatigue.

When glycolysis is enhanced, its byproduct acetyl-CoA is bound to carnitine, leaving less free carnitine to import fatty acids for oxidation. When the glycolysis is reduced, during prolonged exercise or low-intensity exercise, the reduced supply of glycolysis byproducts saves a greater amount of free carnitine that can be used for the transport and oxidation of fatty acids into mitochondria.

Next time you visit a supplement store, you might get more than you came for.

Increases Muscle Mass and Strength

Muscle is probably the main target of carnitine transport as around 90–95% of total carnitine is concentrated in muscle. Carnitine sports supplements have been reported to spare the use of amino acids as energy sources during exercise making them potentially available for new protein synthesis. In fact, one study conducted on dogs demonstrated decreased protein degradation during exercise by using a carnitine sports supplement.

This justifies the use of carnitine fitness supplements to increase muscle mass during endurance exercise. Find a carnitine supplement online that can be a great addition to those barbells you’re thinking of buying.

On the other hand, does l-carnitine burn fat is a common question that has contradicting answers. Due to its glycogen sparing and fatty oxidation effects, carnitine has been recommended to lose weight. However, it’s been noted that increased plasma concentrations of carnitine don’t shift the metabolism to fatty-acid oxidation but actually makes it pick up where it left off. Glucose oxidation continues with the help of carnitine scavenging its byproducts that got in the way.

Furthermore, studies showing both weight loss and no change in weight have been reported. It must be noted that some were performed on athletes while others were performed on obese individuals. The differences in their metabolisms might influence the results. Moreover, it seems like oral carnitine supplements will have little effect if any on muscle carnitine concentration and storage. This is due to its low bioavailability, the low renal threshold for excretion (being near its physiological concentration means that any excess is going to end up in the urine) and low muscle turnover.

Even long-term carnitine administration in humans doesn’t increase muscle carnitine storage. Alternatively, carnitine may have a role in the muscle’s vascular supply. Studies demonstrated increased muscle contractile force and elevated blood flow in dogs even though their muscle carnitine storage was not increased.

To conclude, carnitine might have an effect independent of supplying depleted storage and fatty acid oxidation but it’s more likely related to increasing muscle mass and strength instead of fat loss.



L-carnitine and acetyl-l-carnitine (ALCAR) have been the talk of the town recently due to their neuroprotective effects. Numerous clinical studies have reported the therapeutic benefit of L-carnitine treatment for infants with some inborn errors of metabolism and adults with central or peripheral nervous system injury in adults.

Treatment with L-carnitine supplements improved symptoms of encephalopathy (damage or disease affecting the brain) caused by a long term use of valproate (mood stabiliser). Case reports show improvement with L-carnitine treatment seen in encephalopathy caused by high ammonia levels after gastrointestinal bypass surgery and in encephalopathy due to gluten enteropathy.

In addition, a randomized clinical trial reported progress in Friedreich’s ataxia patients treated with L-carnitine. Friedreich’s ataxia is a genetic, progressively worsening disease that manifests with difficulty walking, loss of sensation in the arms and legs, and impaired speech.

Fatigue Management

In Australia, the total number of new cases of all cancers diagnosed increased from 47,468 in 1982 to 135,133 in 2016. Cancer-related fatigue is one of the most common and most debilitating complications. The damage of the carnitine system due to chemotherapy and consequently its deficiency may cause fatigue due to impaired energy metabolism. Thus, refurnishing the carnitine pool may lessen the fatigue of cancer patients.

Recent studies showed that L-carnitine supplements in patients with cancer were effective in reducing fatigue, increasing lean body mass and improving nutritional status by increasing appetite. In one study of 11 patients, apart from the alleviation of fatigue, their plasma albumin (protein) and lymphocyte count were maintained.

In spite of this, the type of patients who may benefit from these supplements has not been fully defined.

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Support Kidney Function

Secondary carnitine deficiency may also arise from other serious conditions such as hemodialysis or renal tubular dysfunction, resulting in excessive loss of carnitine in urine. Secondary carnitine deficiency may also occur in malnutrition or prematurity. Renal anemia, one of the most common complications of hemodialysis, is due to loss of function of the renal tissue which secretes erythropoietin, an erythrocyte producing hormone. Furthermore, cardiovascular disease is a significant cause of death among dialysis patients.

Several studies supporting the positive influence of L-carnitine in heart disease have been published. Firstly, L-carnitine treatment significantly reduced cardiac cell death in a study on rats with congestive heart failure. Secondly, by measuring the surface electrical impulse of cardiac cells in another study, increased muscle function was observed. Thirdly, carnitine improved cardiac ejection fraction (EF) in patients with a lowered one.

These findings may suggest that carnitine supplements could prevent cardiac events in at-risk patients. In another study, 62 Japanese hemodialysis patients received oral (2 years) and intravenous L-carnitine supplements (1 year). Although no differences were found in the ECG, hemoglobin concentrations increased significantly in both groups of patients.

Infertility Treatment

L-Carnitine has several benefits in the management of infertility. Regarding male infertility, carnitine supplements help with the maturation of spermatozoa and soften the blow of reactive oxygen species (ROS), free radicals and oxidative stress. In female oocytes, maintenance of proper lipid oxidation with/without a minimum production of free radicals is crucial to preserve their quality.

Most of the human research has been carried out using L-carnitine as a supplement to alleviate/combat the problem of female infertility. Several studies showed improvements in patients with polycystic ovary syndrome, endometriosis and amenorrhea using both L-Carnitine and acetyl-L-carnitine supplements. Also, improvments in sex hormone levels and oocyte health have been reported.

Author: Christina Stone

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