L-carnitine is a natural substance that is found in many foods. It helps to transport fat into cells, where it is burned for energy. It also may improve heart health and aid in weight loss.

Supplemental carnitine is available in different forms, but the acetyl L-carnitine form has the best absorption rate. It is often used in sports supplements due to its benefits for athletic performance and aiding fat burning.

Benefits

Carnitine helps increase the number of calories that your body burns during exercise. This is because carnitine transports fat into the mitochondria to be used as fuel. It also reduces the buildup of lactic acid in muscles after intense exercise, which can cause pain and fatigue.

Older adults who eat less meat or dairy products may be deficient in carnitine. In a randomized trial, supplementing with carnitine increased the amount of fat burned during moderate-intensity exercise.

L-carnitine reduces symptoms of chronic heart failure in people with a history of angina pectoris and improves cardiac function. This is likely due to its antioxidant properties, which help to neutralize harmful free radicals. It also increases the production of brain natriuretic peptide, a marker of improved heart health.

Carnitine supplements have been shown to decrease muscle wasting in people who are recovering from cancer or who are undergoing chemotherapy. However, more research is needed. One early study found that intravenous propionyl L-carnitine reduced the severity of cancer-related fatigue and improved quality of life in survivors of cancer (102). Other studies have not found a benefit from oral carnitine supplementation (107). Several studies show that acetyl L-carnitine is better than placebo for reducing cancer-related fatigue and improving quality of life.

Side effects

L-carnitine increases fat burning and energy levels in muscles. It decreases lactate and pyruvate concentrations in the blood during exercise and enhances recovery from exercise. In one study, a group of recreationally active patients taking 3000 mg of carnitine per day for seven weeks had reduced muscle pain and creatinine kinase levels.

Carnitine also transports long-chain fatty acids into mitochondria, where they are oxidized for energy production. It reduces inflammation, moderating oxidative stress and may decrease triglyceride levels in patients with heart disease. It also prevents fatty acid ester accumulation during ischemic events, decreasing the risk of fatal ventricular arrhythmias.

Carnitine has been suggested to help treat frailty, a syndrome prevalent in the elderly population. This disorder is characterized by unintentional weight loss, weakness, exhaustion, slowness and a decreased ability to perform daily activities. However, research on this potential use of carnitine is limited. Several studies have reported that adding carnitine to standard treatment for heart failure improves measures of cardiac functional capacity and may reduce mortality.

Dosage

The carnitine that is not taken up by enterocytes or reabsorbed from the stool is degraded to two principal products, trimethylamine and g-butyrobetaine. The latter is excreted in the feces; the former is metabolized to acetyl L-carnitine, an important neurotransmitter.

Supplemental carnitine is being investigated in a number of health conditions, including Alzheimer's disease and dementia (see the article on Acetyl L-Carnitine), cardiovascular disease and peripheral artery disease, insulin resistance and diabetes, infertility, osteoarthritis and athletic performance enhancement. It may increase energy expenditure and reduce muscle soreness during intense exercise.

In a randomized placebo-controlled trial in recreationally active subjects, carnitine supplementation (4 g/day orally) improved measures of insulin resistance and increased time to fatigue on a cycle ergometer, endurance and maximal oxygen uptake (VO2max). It also decreased the accumulation of lactate and improved perceived exertion during exercise. A more recent study in adults identified as "pre-frail" showed that supplemental carnitine reduced Frailty Index and hand grip test scores when compared to placebo.

Sources

Carnitine is a nutrient that helps transport fats into cells to be burned for energy. It is produced naturally in the body and is also available as a dietary supplement. Studies have shown that supplemental carnitine may improve endurance, increase fat burning and enhance athletic performance. It also protects against muscle damage and improves brain function.

Carnitine is present in animal products, especially red meat, and dairy foods. Vegetables and grains provide very small amounts of carnitine. In the body, carnitine is made from the amino acids methionine and lysine in a multistep process involving several cell compartments. Methionine is methylated to e-N-trimethyllysine by methyltransferases, and this compound is converted to carnitine in the liver and skeletal muscles by protein hydrolysis.

Methionine and lysine can also be obtained from dietary sources, such as whole grain bread, cereals, oatmeal, beans, cashews, peanuts, cottage cheese and eggs. Supplemental carnitine is sometimes used as an aid in weight loss because it can help transport fats into cells where they are burned for energy.