- Vitamin BT
- Vitamin B7
For Patients & Caregivers
Clinical trials show that carnitine is helpful in patients with angina, heart disease, and peripheral vascular disease.
Carnitine is a molecule found naturally in the body and in foods such as meat and dairy products, beans, and avocados. Its role in the body is extremely important for the production of energy: carnitine “shuttles” fatty acyl CoA across the membrane of the mitochondria so that they can be metabolized and ATP (the “fuel” of every cell) produced. When there is not enough carnitine in the cells, or when there are not enough nutrients in the cells because blood is not reaching the tissues (i.e., ischemia), fatty acyl coA can accumulate outside of mitochondria and cause damaging effects. In general, people with genetic carnitine deficiency are fatigued because energy production is greatly reduced, and they respond well to carnitine supplements.
The use of carnitine supplements for other conditions is less well established. In clinical trials, cancer patients who have higher blood levels of carnitine generally have higher functioning and more energy, probably because their mitochondria are functioning more efficiently. When rats that have the equivalent of heart disease are fed carnitine, they have increased heart performance and smaller areas of damaged heart muscle than rats with heart disease that were not fed carnitine. Similar results have been shown in humans: patients who take carnitine after having a heart attack generally have increased heart performance and exercise tolerance.
Other effects of carnitine that are under study include a protective effect against the damaging effects of cisplatin on the kidney and small intestine and an ability to suppress thyroid hormone.
- To treat Alzheimer’s disease
No scientific evidence supports the use of carnitine for Alzheimer’s disease.
- To treat angina
Several clinical trials suggest that carnitine can increase exercise tolerance in patients with stable angina.
- To gain weight and prevent weight loss in patients with cachexia (muscle wasting) from advanced cancer or HIV/AIDS
No scientific evidence supports this use.
- To manage heart disease
Several clinical trials have suggested that carnitine can enhance physical performance, reduce heart damage after a heart attack, and possible increase survival in patients with heart disease.
- To relieve some of the side effects of chemotherapy
Data are mixed on carnitine’s benefits against chemotherapy-related fatigue.
- To treat chronic fatigue syndrome
One clinical trial supports this use.
- To manage COPD (chronic obstructive pulmonary disease)
No scientific evidence supports this use.
- To improve circulation
Several clinical trials have shown beneficial effects of both carnitine and propionyl-L-carnitine on peripheral vascular disease.
- To treat diabetes
One clinical trial showed that continuous infusion of carnitine decreased insulin resistance in patients with type 2 diabetes, but more research is needed to confirm this effect. Studies generally do not support the use of carnitine or acetyl-L-carnitine for treating diabetic neuropathy.
- 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
One study showed that carnitine may be useful in treating idiopathic male infertility. More studies are needed.
- For increased strength and stamina
Studies of oral carnitine for enhanced exercise performance in healthy individuals are poorly designed and show no consistent benefit.
- Over-the-counter carnitine supplements may have poor bioavailability, meaning that they may not be well absorbed into the bloodstream through the gut.
- 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, the acetylated form, which can increase chemotherapy-induced peripheral neuropathy.
For Healthcare Professionals
Carnitine is an endogenous cofactor in intermediary metabolism. Patients use this supplement to enhance physical performance and to treat fatigue and cachexia associated with carnitine deficiency caused by end-stage renal disease, cardiovascular disease, cancer, diabetes, chronic fatigue syndrome, and AIDS. Endogenous treatment is thought to enhance mitochondrial integrity and function.
L-carnitine demonstrated a protective effect against statin-induced cellular damage via its anti-oxidative properties in rat hepatocytes (31).
Preliminary results indicate benefits of l-carnitine in improving symptoms of Chronic Fatigue Syndrome (22) and improving physical performance in patients undergoing dialysis for end-stage renal disease (9), but data of its benefits in alleviating atigue associated with multiple sclerosis are inconclusive (21). L-carnitine has been used to prevent skeletal muscle myopathy in heart failure and to block apoptosis (14), and may help prevent cardiovascular disease (24). Several trials have shown enhanced physical performance (6) (17) (20), mitochondrial metabolism (9), or survival (7); supplementation was found to improve aerobic capacity and exercise tolerance in patients with mitochondrial myopathy (32). Beneficial effects of both carnitine and propionyl-L-carnitine were seen in trials of peripheral arterial disease (1). L-carnitine used by itself or in combination with clomiphene citrate may help in the treatment against idiopathic male infertility (25).
L-carnitine may also benefit cancer patients. Supplementation was shown to improve the quality of life in pancreatic cancer patients (27). Preliminary data show that L-carnitine by itself (15) (23) or in combination with Coenzyme Q (33) plays a role in ameliorating chemotherapy-related fatigue. But conflicting data from another study do not support such benefit (28). More research is needed.
Carnitine plays a role in the transport of long chain fatty acyl CoA esters across the inner mitochondrial membrane, facilitating beta-oxidation of fatty acids and acting as an intracellular energy reservoir of acetyl groups. In conditions of ischemia and carnitine deficiency, these acyl esters accumulate and cause deleterious effects, including inhibition of adenine nucleotide translocase, causing inhibition of ATP production (5). Carnitine modulates the ratio of CoA to CoA-SH, is involved in trapping acyl residues from peroxisomes and mitochondria, and stabilizes cellular membranes (6). It is a free radical scavenger and may take part in nuclear transcription.
High serum carnitine levels generally correlated with better functional capacity in clinical trials. Exogenous carnitine enhanced mitochondrial function in several studies, thought due to an increase in fatty acid oxidation and conservation of glycogen or a decrease in levels of acetyl-CoA, which inhibits pyruvate dehydrogenase (1). In ischemic animal models, carnitine reduced loss of high-energy phosphates, enhanced glucose oxidation, preserved myocardial carnitine stores, reduced accumulation of fatty acid esters, and enhanced lactate extraction. Numerous studies report that carnitine supplementation improved cardiac performance in animal models of cardiomyopathy or ischemic insult, including improved myocardial metabolic patterns, reduced necrosis, diminished enzymatic infarct size, and preserved left ventricular function (8). L-carnitine has been shown to inhibit cisplatin-induced injury of the kidney and small intestine in animal models (13). One study suggested that L-carnitine inhibits caspases and decreases levels of TNF-alpha (14).
A few mechanisms that result in the anti-catabolic effects and the improvement of fatigue following l-carnitine supplementation include affecting improved nitrogen balance either due to increased protein synthesis or reduced protein degradation, inhibition of apoptosis and abrogation of inflammatory processes. Animal studies indicate that carnitine supplementation prevents oxidative stress and ameliorates mitochondrial function (29).
In a mice model metabolism of dietary l-carnitine by intestinal microbiota produced trimethylamine-N-oxide (TMAO), a proatherogenic species, which accelerated atherosclerosis (30). Clinical trials are needed to determine the implications of this study in humans. Long-term carnitine supplementation in humans is correlated with improved myocardial mechanical performance, reduction in ventricular arrhythmias, and increased exercise tolerance (7). In one study carnitine was shown effective in reversing hyperthyroidism by acting as a peripheral antagonist of thyroid hormone action (3).
A patient with riboflavin-responsive mild multiple acyl-CoA dehydrogenation deficiency of the ethylmalonic-adipic aciduria type experienced repeated hypoglycemic episodes while taking L-carnitine supplements. Patients with defective oxidation of medium- or short-chain fatty acyl-CoA esters should use carnitine supplementation with caution.