- Vitamin BT
- Vitamin B7
For Patients & Caregivers
How It Works
Some clinical trials show that carnitine supplementation is helpful for patients with angina, heart disease, or peripheral vascular disease. However, guidelines recommend against a particular form, acetyl-l-carnitine, for chemotherapy-induced peripheral neuropathy.
Carnitine is a nutrient found naturally in the body and in foods such as meat and dairy products, beans, and avocados. It plays an important role in energy production by delivering fatty acids that are processed within the cells to be used as fuel. It also helps to prevent damaging effects that can occur when fatty acids build up outside of cells.
L-carnitine is more readily absorbed in the body if obtained from food rather than supplements. However some people, such as those with a genetic deficiency who are fatigued because energy production is greatly reduced, respond well with carnitine supplements. In addition, studies in some patients with heart conditions show improved heart function and ability to exercise after taking carnitine.
There is less evidence for the use of carnitine supplements for other conditions. In clinical trials, cancer patients who have higher blood levels of carnitine generally have higher functioning and more energy. However, one particular form, acetyl-L-carnitine, is known to increase chemotherapy side effects, so it is important to discuss any use of this supplement with your oncologist.
- To manage heart disease Several clinical trials suggest that carnitine can enhance physical performance, increase exercise tolerance in patients with stable angina, reduce heart damage after a heart attack, and possibly increase survival in patients with heart disease. It may improve circulation in peripheral vascular disease. However, results from one large trial of patients who had a heart attack found no reductions in heart failure events or death with carnitine therapy.
- To relieve some side effects of chemotherapy Data are mixed on whether carnitine helps chemotherapy-related fatigue. In addition, a processed form of carnitine known as acetyl-L-carnitine, has been shown to increase nerve pain. Therefore, additional studies are needed to determine whether carnitine supplementation can benefit cancer patients.
- To gain weight and prevent weight loss in patients with advanced cancer There is some initial evidence that carnitine supplementation may improve nutritional status in patients with advanced pancreatic cancer while improving quality of life. However, additional studies are needed to confirm these effects.
- To treat chronic fatigue syndrome One clinical trial supports this use.
- To treat diabetes In one clinical trial, carnitine given by infusion decreased insulin resistance in patients with type 2 diabetes, but more research is needed to confirm this effect with oral dosages. A few studies also suggest that carnitine may be helpful for diabetic nerve pain.
- To lower high cholesterol Although several clinical trials suggest that carnitine supplements can increase HDL (“good”) cholesterol and reduce blood triglyceride levels, several other clinical trials contradict these findings.
- To treat infertility Studies show mixed results in treating male infertility.
- To increase strength and stamina Studies of oral carnitine for enhanced exercise performance in healthy individuals are poorly designed and show no consistent benefit.
- To treat Alzheimer’s disease Some clinical trials show benefit with a processed form of carnitine known as acetyl-L-carnitine to improve brain function, but two large long-term studies did not find any benefit. In addition, a review of studies on various forms of carnitine to enhance brain function found the current evidence lacking.
- Over-the-counter carnitine supplements may not be well absorbed by the body.
- L-carnitine may inhibit the action of thyroid hormone, but it is not known whether it interacts with thyroid supplements.
- L-carnitine should not be confused with acetyl-L-carnitine, which can increase chemotherapy side effects such as nerve pain.
For Healthcare Professionals
Carnitine is a nutrient that plays an important role in fatty acid absorption and mitochondria function. It can be found in diets that include meat, or synthesized endogenously from lysine and methionine. Deficiencies can be caused by genetic disorders, malnutrition, malabsorption, and kidney dialysis. These can affect the heart, skeletal muscles, liver, nerve, and endocrine functions. Carnitine is marketed as a dietary supplement to enhance physical performance and to treat fatigue, cardiovascular disease, diabetes, obesity, chronic fatigue syndrome, liver disorders, and cancer.
Animal models suggest that L-carnitine has cardioprotective (8) (14) and antioxidant effects (31). It may help prevent cardiovascular disease in hemodialysis patients (24). Long-term carnitine supplementation in humans is correlated with improved myocardial mechanical performance, reduction in ventricular arrhythmias, and increased exercise tolerance (7). However, L-carnitine administration did not improve risk of death or heart failure in patients with anterior acute myocardial infarction (36).
Preliminary results suggest L-carnitine may improve symptoms of chronic fatigue syndrome (22) and physical performance in patients undergoing dialysis for end-stage renal disease (9), but data of its benefits in alleviating fatigue associated with multiple sclerosis are inconclusive (21). Several trials have shown enhanced physical performance (17) (20), and improved aerobic capacity and exercise tolerance (32). Other studies show mixed results (37) (38) (39) and its clinical value and safety needs additional study.
L-carnitine used by itself or in combination with clomiphene citrate may help in the treatment against idiopathic male infertility (25), although it did not improve sperm count or motility (40). Oral carnitine supplementation may improve mental health parameters and biomarkers of oxidative stress in women with polycystic ovary syndrome (2).
There are studies looking into the effects of carnitine in cancer patients. L-carnitine supplementation improved nutritional status and quality of life in pancreatic cancer patients (27). Other preliminary data show that L-carnitine by itself (15) (23) or in combination with Coenzyme Q10 (33) may relieve chemotherapy-related fatigue. L-carnitine also demonstrated benefits against fatigue both in younger hypothyroid patients receiving levothyroxine and thyroid cancer patients who have hypothyroidism post-surgery (41). However, carnitine does not improve fatigue in patients with invasive malignancies (28). Other preliminary data suggest l-carnitine may reduce vismodegib-associated muscle spasms (52). Additional studies are needed to determine the cancer populations in which carnitine supplementation may be most beneficial.
An ester derivative, acetyl-L-carnitine, is also available as a dietary supplement and is often used as a neuroprotective agent. It may help to reduce diabetic neuropathy (42) (43) or improve cognition in patients with severe hepatic encephalopathy (44). In elderly patients with dysthymic disorder, it was found to be comparable with fluoxetine (45); however, other studies did not find it effective for Alzheimer’s disease (46) (47). One study actually showed that acetyl-L-carnitine can increase chemotherapy-induced peripheral neuropathy (CIPN) (35), and this negative effect persisted at long-term follow-up over 2 years (53). Guidelines also do not recommend acetyl-l-carnitine to prevent chemotherapy-induced peripheral neuropathy because of a possibility of harm (54). Therefore, patients receiving chemotherapy should avoid this product.
Mechanism of Action
Carnitine is a non-essential amino acid, with only the L-isomer utilized in human bodies. It is available in many foods, and bioavailability from dietary sources is much higher (54–87%) than from oral supplements (14%–18%) (48). L-carnitine plays a role in the transport of long chain fatty acids across the inner mitochondrial membrane, facilitating beta-oxidation of fatty acids and acting as an intracellular energy reservoir of acetyl groups. In deficiencies, these acyl esters accumulate and cause deleterious effects including inhibition of adenine nucleotide translocase, which impedes ATP production (5). Carnitine supplementation prevents oxidative stress and ameliorates mitochondrial function (29). L-carnitine demonstrated a protective effect against statin-induced cellular damage via its anti-oxidative properties in rat hepatocytes (31).
Animal studies show L-carnitine has cardioprotective effects by preventing skeletal muscle myopathy (14). In hemodialysis patients, carnitine has antiinflammatory and anticoagulation effects which may contribute to its cardioprotective activity (24).
In cardiac disease models, carnitine supplementation improved cardiac performance including improved myocardial metabolic patterns, reduced necrosis, diminished enzymatic infarct size, and preserved left ventricular function (8). Its effects on congestive heart failure-associated myopathy may be due to caspase inhibition and decreased TNF-alpha levels (14). Metabolism of dietary L-carnitine by intestinal microbiota produced trimethylamine-N-oxide (TMAO), a proatherogenic species, which accelerated atherosclerosis (30).
Carnitine is often proposed for the treatment of obesity and metabolic syndrome. Possible mechanisms include inhibition of stearoyl-CoA desaturase-1 activity, β-oxidation of fatty acids, and increased storage in the body tissues (49).
Animal studies show L-carnitine has anticatabolic effects by improving nitrogen balance either via increased protein synthesis or reduced protein degradation. Other studies show it prevents oxidative stress and ameliorates mitochondrial function (29). It may help cancer-related cachexia by reducing proteasome activity (50). Clinical trials are needed to determine the implications of this study in humans.
In one trial, carnitine was shown to be effective in reversing hyperthyroidism by acting as a peripheral antagonist of thyroid hormone action (3).
Rare: Dyspepsia, heartburn (5).
Hypoglycemia: In a patient with a rare genetic metabolic disorder who took carnitine supplements (11).