L-Carnitine

background

The main function of L-carnitine is to transfer certain fat-soluble molecules in the body across membranes within cells so the molecules can be broken down and used in the Krebs cycle. In humans, L-carnitine is synthesized in the liver, kidney, and brain and actively transported to other areas of the body. For example, 98% of the total body L-carnitine is confined to the skeletal and cardiac muscle at concentrations approximately 70 times higher than in the blood serum.
Supplementation may be necessary in rare cases of primary carnitine deficiency, which may be caused by a defect in the body's production of carnitine, a defect in the transport of carnitine into tissue, or a defect the kidney's ability to conserve carnitine. L-carnitine was shown to be effective in the following conditions which arise from secondary deficiency of L-carnitine: chronic stable angina (chest pain) and intermittent claudication (impaired walking or limping) characterized by low oxygen levels in tissues. Another condition that may benefit from carnitine supplementation is decreased sperm movement. Carnitine supplementation, as L-carnitine, or acetyl- or propionyl-L-carnitine, has been investigated in many other diseases and conditions.
Although use in preterm infants suggests that carnitine supplementation may aid in maintaining or increasing plasma carnitine levels and possibly weight gain, carnitine is not routinely added to preterm total parenteral nutrition (TPN). However, soy-based infant formulas are fortified with carnitine to levels found in breast milk.
In 1986, the U.S. Food and Drug Administration (FDA) approved L-carnitine for use in primary carnitine deficiency. However, D-carnitine or DL-carnitine may cause secondary L-carnitine deficiency and should not be used.

Related Terms

AcCn, acetyl-L-carnitine, B (t) Factor, beta-hydroxy-gamma-N-trimethylamino butyrate, canitor, Carnilean®, carnitene, carnitor, D-carnitine, D,L-carnitine, glycine propionyl-L-carnitine (GPLC), Godex®, L-3-hydroxytrimethylamminobutanoate, LAC, L-acetyL-carnitine, LCLT, L-CARNIPURE, L-Carnipure®, L-carnitina (Spanish), L-carnitine L-tartrate, levacecarnine, levocarnitine, levocarnitine chloride, LK-80, L-propionylcarnitine, propionil-L-carnitine, propionyl-L-carnitine, ST200, ST261, VitaCarn®, vitamin B(t), vitamin Bt.
Selected combination product: PhenCal (phenylalanine, tryptophan, glutamine, pyridoxal-5'-phosphate, chromium picolinate, carnitine).
Note: This monograph focuses on supplemental sources of carnitine (including acetyl-L-carnitine and propionyl-L-carnitine) and not the acyl (fatty acid) derivatives of carnitine made in the body upon metabolism of carnitine. Unless otherwise stipulated, the use of the term carnitine in this monograph implies the levo (l) carnitine and not d-carnitine, which may cause secondary deficiency.

evidence table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
 
Metabolic abnormalities (inborn errors of metabolism related to carnitine metabolism) (Grade: A)
Various inborn errors of metabolism related to carnitine metabolism exist, including genetic disorders related to carnitine-acylcarnitine translocase deficiency. Evidence suggests that carnitine may be used as part of a treatment plan for carnitine-acylcarnitine translocase deficiency, as well as for the management of general inborn errors of metabolism and carnitine uptake defects.
Nutritional deficiencies (primary and secondary carnitine deficiency in adults) (Grade: A)
Primary carnitine deficiency is an extremely rare genetic condition. Secondary deficiency is a deficiency in carnitine due to other factors. Evidence from case reports and reviews suggests that carnitine, given by mouth or injected into a vein, may used as part of a treatment plan for primary deficiency and various types of secondary deficiencies.
Peripheral vascular disease (blocked arteries in the legs) (Grade: A)
Well-designed studies indicate that propionyl-L-carnitine and L-carnitine may be beneficial for the treatment of blocked arteries in the legs, especially in those cases when there are severe limitations in peripheral circulation. It is not clear, however, whether angiopathies (blood vessel diseases) caused by atherosclerosis (hardening of the arteries) or diabetes are equally sensitive to the carnitine agents.
Angina (long-term chest pain from clogged heart arteries) (Grade: B)
Evidence from well-designed clinical trials suggests that L-carnitine and propionyl-L-carnitine are effective in reducing symptoms of chest pain due to clogged heart arteries. Possible increases in exercise tolerability have also been suggested as a result. Carnitine may not offer further benefit when patients continue conventional therapies. More high-quality studies are needed before a firm conclusion can be made.
Autism (Grade: B)
Evidence from well-designed studies and reviews indicates that carnitine may offer benefit for individuals with autism. Further research is required before conclusions can be made.
Dialysis (hemodialysis) (Grade: B)
Good evidence suggests that, for hemodialysis patients, carnitine given by mouth may increase levels of carnitine in the blood, enhance red blood cell survival, reduce heart or inflammatory disease risk factors, and improve quality of life. However, further research is required to understand the specific areas of benefit in this population.
Hepatic encephalopathy (confused thinking due to liver disorder) (Grade: B)
Evidence from well-designed trials suggests that L-carnitine may improve the quality of life and mental functioning of individuals with confused thinking due to liver disorders. Further well-designed research is required in order to determine optimal dose and timing. Also, the evidence is limited by the majority of studies being conducted by the same research group.
Infertility (male) (Grade: B)
Evidence from well-designed trials, systematic reviews, and meta-analyses suggests that carnitine and/or acetyl-L-carnitine may increase sperm movement and pregnancy rates. Further information is required with respect to dosing and duration, as well as the type of male infertility most likely to be benefited.
ADHD (Grade: C)
Limited research has examined the effects of L-carnitine in boys with attention-deficit hyperactivity disorder (ADHD). Although results were promising, well-designed trials are needed before conclusions can be made. Furthermore, other research has indicated that cotreatment with carnitine and conventional ADHD treatment (methylphenidate) lacks additional benefit over conventional treatment alone.
Aging (Grade: C)
Carnitine may alter body composition, decrease fatigue, and improve physical and mental functioning in individuals over 100 years of age. However, further research is required in this field.
AIDS (Grade: C)
Limited evidence suggests that carnitine may increase proliferation of mononuclear cells and increase in CD4 counts in patients experiencing acquired immune deficiency syndrome (AIDS). However, the effect of carnitine on body fat and lipid (fat) levels associated with antiretroviral drugs was mixed. In order for conclusions to be made, well-designed studies are needed.
Alcoholism (Grade: C)
Clinical trials suggest that L-carnitine or acetyl-L-carnitine may be of benefit to alcoholics. Well-designed clinical trials are required before conclusions can be made in this field.
Alertness (Grade: C)
Limited evidence suggests that a combination product containing acetyl-L-carnitine can aid alertness in college students. Further research is required.
Alopecia (hair loss) (Grade: C)
In limited research, carnitine increased hair growth in individuals with mild-to-moderate androgenetic alopecia (male-pattern baldness). Further well-reported research is required before conclusions can be drawn.
Alzheimer's disease (Grade: C)
Results from early studies suggested that L-carnitine and/or acetyl-L-carnitine may be beneficial for Alzheimer's disease. Also, a combination product containing acetyl-L-carnitine, vitamins B12 and E, and other compounds significantly delayed mental decline (based on the Dementia Rating Scale), and improved behavioral symptoms (based on the Neuropsychiatric Inventory) and maintenance of performance. However, conflicting results exist. Better-designed clinical trials are required before conclusions can be made in this field.
Amenorrhea (lack of menstrual period) (Grade: C)
Although preliminary results are promising, there is a lack of well-designed and reported clinical trials investigating the effect of L-carnitine on amenorrhea (the lack of menstruation). Well-designed and reported clinical trials are required before conclusions can be made.
Arrhythmia (abnormal heart rhythm) (Grade: C)
Although preliminary results are promising, there is a lack of well-designed and reported clinical trials investigating the effect of L-carnitine on arrhythmia (abnormal heart rhythm). Well-designed and reported clinical trials are required before conclusions can be made.
Arthritis (Grade: C)
Limited evidence suggests that carnitine may offer benefit for childhood psoriatic onycho-pachydermo-periostitis (POPP; a subset of psoriatic arthritis). Further research is required before conclusions can be made.
Beta-thalassemia (fewer red blood cells and less hemoglobin) (Grade: C)
Carnitine may increase the effectiveness of hydroxyurea therapy in patients with beta-thalassemia intermedia. Although there is some evidence of benefit in these patients with carnitine alone, the endpoints are diverse and the quality of publication is poor. Therefore, the effect of carnitine alone is not clear, and further research with specific endpoints is required before conclusions can be made.
Brain injuries (Grade: C)
Limited evidence indicates that acetyl-L-carnitine, used in combination with weight loss, vitamins, antioxidants, and nutrients to enhance blood flow, may improve sports-related brain injuries. In addition, carnitine injected into the vein may promote awakening from comatose thyroid storm. However, the effect of carnitine alone is not clear, and further research is required before conclusions can be made.
Cachexia (weight loss/wasting from some diseases) (Grade: C)
Limited evidence suggests that carnitine had a lack of effect on fatigue, energy expenditure, and lean body mass in patients with cachexia due to cancer. Further research is required before conclusions can be made.
Cancer (Grade: C)
Limited studies have evaluated carnitine as part of a treatment plan for pancreatic cancer and a certain type of advanced thyroid cancer. The effect of carnitine alone is not clear, and further research is required before conclusions can be made.
Cardiovascular disease (heart disease) (Grade: C)
Limited evidence suggests that, in patients with heart disease, carnitine in combination with other agents, such as fasudil, may improve blood pressure levels. However, further research is required.
Cardiovascular disease risk (Grade: C)
Limited evidence indicates that, in healthy individuals and individuals with type 2 diabetes, carnitine may reduce levels of cardiovascular disease risk factors. However, further research is required.
Cerebral ischemia (a lack of adequate blood flow to the brain) (Grade: C)
A limited number of studies have shown a positive effect of acetyl-L-carnitine on blood flow to the brain and metabolism of the brain in patients who have suffered from stroke. Well-designed clinical trials are required before conclusions can be made.
Chronic fatigue syndrome (Grade: C)
Preliminary evidence suggests a potential benefit from carnitine in patients with chronic fatigue syndrome, due to an altered metabolism of acyl-carnitine in these individuals. Well-designed clinical trials are required before conclusions can be drawn.
Dementia (elderly) (Grade: C)
Most of the studies related to dementia suffer from various weaknesses. Although preliminary evidence is promising, there is currently inadequate evidence to conclude for or against the use of acetyl-L-carnitine for dementia. Well-designed clinical trials are required before conclusions can be made.
Depression (Grade: C)
Although the limited results are promising, there is insufficient evidence to support the use of carnitine in the treatment of depression. Well-designed clinical trials with adequate subject numbers are required.
Diabetes mellitus (Grade: C)
Limited evidence suggests that constant infusion of L-carnitine may increase insulin sensitivity in patients with type 2 diabetes mellitus and enhance glucose (sugar) oxidation. These results need to be confirmed in long-term studies. Some studies suggest that carnitine may decrease fasting blood glucose and lipoprotein levels, but results are not consistent. Well-designed clinical trials are still required before firm conclusions can be made.
Diabetic nerve damage (neuropathy) (Grade: C)
Preliminary evidence suggests that acetyl-L-carnitine may be beneficial for individuals with diabetic nerve damage. However, more well-designed clinical trials are required before conclusions can be made.
Dialysis (CAPD) (Grade: C)
Limited research has investigated the effect of L-carnitine in patients receiving continuous ambulatory peritoneal dialysis (CAPD). A beneficial effect of carnitine on hypertriglyceridemia (increased levels of fatty compounds that are associated with blood vessel hardening) was lacking. Better-designed clinical trials are required before conclusions can be made.
Diphtheria (throat disease) (Grade: C)
Preliminary evidence suggests that carnitine may reduce heart muscle damage in patients with diphtheria (a certain throat disease). However, more well-designed trials should be performed to confirm these results.
Down's syndrome (Grade: C)
Preliminary evidence suggests that acetyl-L-carnitine may not be beneficial for patients with Down syndrome. Additional well-designed trials are required.
Drug withdrawal (Grade: C)
Preliminary evidence suggests that acetyl-L-carnitine may be beneficial for withdrawal from opiates. Additional well-designed trials are required.
Elimination of toxins (drugs) (Grade: C)
Limited evidence suggests that carnitine may be used as part of a treatment plan for toxicity associated with various drugs. For instance, carnitine may reduce valproate-induced liver injury. In addition, acetyl-L-carnitine may reduce HIV-associated antiretroviral toxic nerve damage. The effect of carnitine on chemotherapeutic toxicity has also been examined, but conclusions cannot be drawn at this time. Additional well-designed studies are needed.
Erectile dysfunction (Grade: C)
Preliminary studies suggest that propionyl-L-carnitine, with acetyl-L-carnitine or sildenafil, may be beneficial for patients with erectile dysfunction (ED). However, more rigorous trials should be performed to determine the effectiveness of carnitine for routine use in ED.
Exercise performance (Grade: C)
Overall, the data are mixed in terms of benefits of L-carnitine for exercise performance. Until confirmed, the advisability of use of L-carnitine for increased exercise endurance is unclear.
Fatigue (Grade: C)
Some evidence suggests that L-carnitine may be an effective treatment for fatigue. However, due to the different populations studied, it is difficult to draw conclusions. Well-designed clinical trials are required in specific populations before conclusions can be made.
Fibromyalgia (long-term musculoskeletal disorder) (Grade: C)
Limited evidence suggests that L-carnitine may be a beneficial treatment for the long-term musculoskeletal disorder called fibromyalgia. Further research is required.
Fragile-X syndrome (Grade: C)
There is insufficient evidence to support the use of carnitine in the treatment of hyperactive behavior of children with fragile-X syndrome. Further well-designed clinical trials are still required.
Heart failure (CHF) (Grade: C)
Despite strong evidence in animal and human studies that congestive heart disease is associated with reduced levels of carnitine in heart muscles, the number of well-organized studies demonstrating the efficacy of carnitine supplementation is small. Further well-designed clinical trials are required before conclusions can be made.
Huntington's chorea/disease (Grade: C)
Limited evidence suggests that acetyl-L-carnitine possesses neither efficacy nor toxicity towards the patients with Huntington disease. Further trials are required before conclusions can be made.
Hyperlipoproteinemia (high levels of lipoprotein and cholesterol in the blood) (Grade: C)
Although preliminary evidence is promising, well-designed clinical trials are still required to determine the beneficial effect of carnitine on hyperlipoproteinemia (high levels of cholesterol in the blood).
Hyperthyroidism (overactive thyroid) (Grade: C)
Limited evidence indicates that carnitine may have beneficial effects on symptoms associated with hyperthyroidism (an overactive thyroids). However, currently there is not enough evidence to determine the use of carnitine as a treatment for this condition.
Lactic acidosis (lactic acid buildup) (Grade: C)
There are a limited number of studies relevant to the use of carnitine for lactic acidosis (lactic acid buildup). There is not sufficient evidence to make a conclusion for the use of carnitine for this condition.
Liver disease (Grade: C)
There are a limited number of studies relevant to the use of carnitine for liver disease. Some early promising results were obtained, but there is not sufficient evidence to make a conclusion for the use of carnitine in the treatment of liver cirrhosis.
Memory (Grade: C)
There are a limited number of studies relevant to the use of carnitine for memory. However, carnitine's use lacked effect unless taken with a glucose drink; the glucose drink alone also appeared to be beneficial. Thus, more trials are required in this field before conclusions can be made.
Metabolic abnormalities (Grade: C)
Carnitine has been used as part of a treatment regimen in pregnant women with metabolic abnormalities such as methylmalonic acidemia (MMA) and cobalamin C (cblC) deficiency, methylmalonic acidemias and acidurias, and isovaleric academia, as well as in siblings or infants with a mutation of methylmalonyl-CoA mutase gene, and propionic academia (PA). However, the benefits are still unclear, and further studies are needed.
Mitochondrial disorders (Grade: C)
Carnitine has been used as part of a treatment plan for various mitochondrial disorders. The use of carnitine for genetic mitochondrial disorders has been discussed by various authors. Further research is required due to the limited number of such disorders in existence.
Multiple sclerosis (Grade: C)
Based on only limited research, there is inconclusive evidence that carnitine is helpful for multiple sclerosis (MS)-related fatigue. Further research is required.
Myocardial infarction (heart attack) (Grade: C)
Limited evidence suggests a decline in the size of an infarction (heart attack) with carnitine treatment. Well-designed studies are needed to make conclusions on the use of L-carnitine for the treatment of acute infarction.
Nutritional deficiencies (adults) (Grade: C)
Limited evidence suggests that the use of carnitine lacks an effect on the metabolism of lipid components of parenteral nutrition. Thus, currently there is insufficient evidence to support the use of carnitine in total parenteral nutrition (TPN) for adults.
Nutritional deficiencies (full-term infants) (Grade: C)
It is not clear whether full-term infants receiving total parenteral nutrition (TPN) need additional carnitine. For long-term feeding with plant-derived proteins such as soy formula, carnitine may be added to levels found in breast milk. However, it is unclear what effect, if any, the addition of carnitine has on weight gain. Carnitine in TPN has offered mixed results, although increased carnitine status has been noted. Further studies are needed.
Nutritional deficiencies (premature infants) (Grade: C)
Despite a large number of studies, it is not clear whether premature infants receiving total parenteral nutrition (TPN) need additional carnitine. Limited evidence suggests that additional carnitine may cause adverse effects in terms of weight gain. Thus, it is not advisable to use carnitine in TPN in low-birthweight infants, without evidence of need. For long-term feeding with plant-derived proteins such as soy formula, carnitine may be added to levels found in breast milk. However, It is unclear what effect, if any, the addition of carnitine has on weight gain. Further studies are needed.
Obesity (Grade: C)
According to limited evidence, L-carnitine had a lack of effect on weight loss in obese patients. Further studies are needed before conclusions can be made.
Peripheral neuropathy (pain in hands and feet due to nerve damage) (Grade: C)
Currently there is not sufficient evidence to make conclusions for the use of carnitine as a treatment for peripheral neuropathy (pain in the hands and feet due to nerve damage). Further studies are needed.
Peyronie's disease (Grade: C)
Promising results have been reported for the use of carnitine in individuals with Peyronie's disease. However, further studies are needed to confirm these results.
Pregnancy (miscarriage) (Grade: C)
Limited research has investigated carnitine for threatened miscarriage. However, the sample size was too small to make conclusions. Well-designed clinical trials are needed in this field.
Respiratory distress (adults) (Grade: C)
Limited research has examined carnitine for respiratory distress in adults. As yet, there is insufficient evidence to use carnitine for this condition.
Respiratory distress (infants) (Grade: C)
Limited research has investigated the use of carnitine for respiratory distress in infants. Currently there is not sufficient evidence to support the use of carnitine for this condition.
Rett's syndrome (Grade: C)
Limited studies have shown promising results for the use of carnitine for treating Rett syndrome. Before strong conclusions can be made, additional well-designed trials are required.
Sciatica (back and leg pain) (Grade: C)
According to limited evidence, acetyl-L-carnitine may reduce the sciatic pain due to a herniated disc. Further well-reported research is required before conclusions may be drawn.
Sickle cell disease (Grade: C)
Preliminary evidence suggests the absence of any therapeutic effect of propionyl-L-carnitine for sickle cell disease. Additional studies are required before conclusions can be made.
Surgical uses (bypass) (Grade: C)
The results of studies on the use of carnitine in improving the functioning of the myocardium (heart's muscular tissue) during open-heart surgery are controversial. Currently, there is not enough evidence to make conclusions for the use of carnitine as a treatment for this condition.
Systemic lupus erythematosus (SLE, or lupus) (Grade: C)
Limited evidence is available with respect to carnitine for systemic lupus erythematosus. Further research is required.
Tuberculosis (Grade: C)
Limited evidence suggests that antibacterial activity may be increased in patients with tuberculosus given acetyl-L-carnitine. Well-designed clinical trials are required before conclusions can be made.