The metabolic functions of carnitine have been well studied in the last 50 years. It is known to be an essential element in mitochondrial energy generation and metabolism of acetyl coenzyme A and can be found in many foods, particularly in red meats such as beef, as well as in fish, poultry and milk.  Yes, of course you’ve heard of this amino acid, but do you know what L-carnitine is? Do you know all their functions? We will see!
What is L-Carnitine?
The L-carnitine , the biologically active form involved in the metabolism of fatty acids and in the food, is biosynthesized within the human body using the L-lysine amino acid and L-methionine as substrates, and transports chain fatty acids into the mitochondrial matrix , thus allowing the fat loss and obtaining energy from stored fat reserves . Since L-carnitine and its compounds help to reduce oxidative stress, it has been proposed for the treatment of many conditions, including obesity. [1,2]
What are the benefits of L-carnitine?
It is known to be an essential substance for the treatment of nutritional deficiencies and innate errors of metabolism in infants and children and has been approved by the Food and Drug Administration of the United States since 1985 for the treatment of clinical disorders with substance deficiency. [3-5] But there are other advantages in using L-carnitine as a dietary supplement :
1. Cardiovascular System
70% of the energy required by the heart is provided by fatty acids and L-carnitine helps in the use of these fatty acids as a sustainable and sustainable source of energy for the cardiovascular system. In addition to having benefits in the anti-aging of the heart and improving peripheral circulation (improving peripheral arterial disease and symptoms of intermittent claudication), it still appears to confer protective effects on people who have suffered a heart attack in the past. [6-8]
It is also known to present mechanisms to improve blood pressure in people with high blood pressure , possibly through a mechanism that involves nitric oxide, a substance with a vasodilatory effect that increases blood flow. [9, 10]
2. Neurological system and memory
Due to its unique chemical properties, L-carnitine easily crosses the brain, providing neuroprotective benefits . In addition to stimulating the production of acetylcholine, a powerful neurotransmitter involved in memory and learning, it also increases norepinephrine and serotonin, monoamines that influence mood, anxiety, sleep, eating, among others.  It has also been found to increase glucose and creatine levels in some regions of the brain. Studies have shown that 2 grams of L carnitine daily, over a period of 6 months, are effective in alleviating the side effects of aging.
In addition to helping with age-related changes in memory and mood, reducing neurological decline, deterioration of mental function, and chronic fatigue in older individuals [12,13], L-carnitine appears to protect neurons from toxicity of harmful substances. It can also help regenerate damaged nerves, and is currently being investigated as a therapy in Alzheimer’s disease and in dementia. [14-17] In addition to increasing the release of dopamine (a chemical used between nerve cells) and improving binding to its receptors, it also appears to play an important role in the prevention and reduction of tremor symptoms in Parkinson’s disease . [18,19] On the other hand, in children with attention-deficit hyperactivity disorder and with autism, significant improvements in symptoms have also been observed and may be considered as an adjunct to therapy in the future. [20,21]
3. Reproductive system
Although there was no increase in testosterone levels with L-carnitine, supplementation of 2g daily for 3 weeks increased levels of IGF-3 and theoretically IGF-1 and IGF-2, hormones directly related to growth hormone .  Supplementation with 3g daily also seems to increase sperm quality, especially in aspects related to sperm morphology. However, further studies are needed to evaluate L-carnitine and all the potential biochemical, pharmacological and physiological benefits of the response to carnitine supplementation at the reproductive system level . [4,5]
4. Cancer and hormonal system
Studies with supplementation of 2 grams of L-carnitine daily show a clear improvement in some hormones and consequently in body composition. [1,2]. Since studies with older individuals have shown reductions in fatigue levels (improvement in fatigue-related sleep disorders and fatigue after physical exertion), L-carnitine is currently being studied in the context of chronic fatigue syndrome and cachexia ( muscle wasting). 
What’s more, L-carnitine can help with these same symptoms of fatigue, mood, and sleep in people with advanced cancers. Although it does not prevent cancer, it is currently being tested as a complement to chemotherapy, to help fight fatigue and cachexia, correcting deficiencies that occur in some cases. [4,5]
At the endocrine level, it is also known that despite slightly improving cholesterol levels, especially in older individuals, the results are not statistically significant. However, it appears to have benefits in people with diabetes, increasing insulin sensitivity (a hormone essential in controlling blood glucose levels) and in hemodialysis patients. [6-9]
5. Immune system and infections
It is known that L-carnitine can improve the functioning of the immune system, increasing the functional capacity of macrophages (cells that intervene in defending the body against infections and help eliminate foreign elements to the body). [10,11] Several studies have also analyzed L-carnitine supplementation in the treatment of people with human immunodeficiency virus (HIV). Although the results of these studies are still very preliminary, there is some evidence that doses of 2 to 6 grams of L-carnitine per day can slow the death of lymphocytes (also known as white blood cells, being essential cells in the body’s defense), neuropathy (a nerve problem) caused by HIV, responsible for causing pain and numbness in the hands and feet, and prolonging the lives of people with HIV. [12-14] In addition, there is also some evidence that the immune response to M. tuberculosis infection, responsible for Tuberculosis, can be modulated and improved with substances that act on the neuroendocrine axis, namely what is L-carnitine. 
6. Musculoskeletal System
During exercise, the body requires large amounts of glucose and fatty acids to produce energy, and the relative use of these two substrates during exercise can vary greatly and depends primarily on the intensity of exercise. With L-carnitine, some studies in aerobic conditions have verified a greater preference for the use of fatty acids and a lower use of glucose, which will have benefits in terms of performance and resistance, helping to delay the onset of training exhaustion . [16-19]
In addition, it has been shown that supplementation with L-carnitine prior to high-intensity exercise has some benefit in muscle recovery and reduction of muscle tissue damage, reducing muscle pain after exercise. [20-22] Another study target for this substance is in the prevention of osteoporosis. L-carnitine treatment is known to slow bone loss and improve bone microstructural properties by decreasing bone turnover and aiding in fracture healing in animal models. As such it may be a promising substance in the treatment of patients suffering from loss of bone mass and osteoporosis.