L-carnitine is an amino acid derivative found in most tissues in the human body. It is considered a conditionally essential nutrient in situations where intracellular levels are low. This can be due to certain genetic conditions, mitochondrial dysfunction, diabetes, the aging process, and high-intensity exercise.  

The carnitine shuttle is a critical process for the prevention of the buildup of potentially harmful long-chain substrates and acyl-coenzyme A. Long-chain fatty acids require the carnitine shuttle to facilitate fatty acid transportation. As a result, free carnitine availability may be a factor in the regulation of fatty acid oxidation.  

High amounts of carnitine are found in the muscles of the human body. During physical exercise, mitochondrial fatty acid oxidation is a critical contributor to muscle metabolism. The mitochondrial availability of carnitine during high-intensity exercise can be limited.  

After strenuous exercise, carnitine is believed to be a protective effect against muscle disruption. It may help attenuate the release of creatine kinase and myoglobin. It may also help improve oxidative status and the protein signaling that is important for exercise recovery.  

A review article by Gnoni and colleagues explored the potential role of L-carnitine supplementation in support of energy production during exercise. The authors describe a clinical trial where supplementation with 4 g of carnitine daily for 2 weeks in competitive walkers improved certain exercise-related parameters, including the maximum rate of oxygen consumption (VO2max).  

Other studies involving high performance athletes produced similar results. One study in junior athletes involved 1 g of carnitine supplementation for 6 weeks and reported higher athletic performances. In untrained athletes, study participants experienced slight improvements in exercise performance in a study involving 2 g of carnitine daily for 2 weeks. However, due to the relatively small sample size in these clinical trials, more research is needed to draw further conclusions. 

Carnitine plays other roles within the human body. It has been shown to help support the transference of toxic compounds out of the mitochondria. It also may play a neuroprotective role. The acetyl derivative of L-carnitine, ALC, has been shown to pass through the blood-brain barrier at greater efficiency than L-carnitine. ALC has been shown in research to support the body’s response to oxidative stress and inflammation. 

ALC participates in glycogen synthesis, glucose metabolism modulation, increasing plasma adenosine triphosphate (ATP) concentration, and neurological function. In particular, ALC facilitates cholinergic neurotransmission directly by providing an acetyl group for acetylcholine synthesis.  

L-carnitine is a molecule critical for cellular health and energy production. It may also help support exercise performance and recovery.  

By Colleen Ambrose, ND, MAT