L-Carnitine: What does it do?

L-carnitine is made in the body from the amino acids lysine and methionine, and is needed to release energy from fat. It transports fatty acids into mitochondria, the powerhouses of cells. In infancy, and in situations of high energy needs, such as pregnancy and breast-feeding, the need for L-carnitine can exceed production by the body. Therefore, L-carnitine is considered a "conditionally essential" nutrient.¹

L-carnitine’s actions appear to be particularly important in the heart. As an example, patients with diabetes and high blood pressure were given 4 grams of L-carnitine per day in an preliminary study.² After 45 weeks, irregular heartbeat and abnormal heart functioning decreased significantly compared with nonsupplemented patients. For congestive heart failure, much of the research has used a modified form of carnitine called propionyl-L-carnitine (PC). In one double-blind trial, using 500 mg PC per day led to a 26% increase in exercise capacity after six months.³ In other research, patients with congestive heart failure given 1.5 grams PC daily for 15 days had a 21% increase in exercise tolerance and a 45% increase in oxygen consumption.⁴

Research shows that people who supplement with L-carnitine while engaging in an exercise regimen are less likely to experience muscle soreness.⁵ However, the belief that carnitine’s effect on energy release will help build muscle or improve athletic performance has, so far, not been supported by most research.^{6 7} In a double-blind study of trained athletes, supplementation with 2 grams of L-carnitine two hours before and after a 20 km run failed to improve physical performance or exercise recovery.⁸

L-carnitine has been given to people with chronic lung disease in trials investigating how the body responds to exercise, however.^{9 10} In these double-blind reports, 2 grams of L-carnitine taken twice per day for two to four weeks led to positive changes in lung function and metabolism during exercise.

Beta thalassemia major is an inherited, fatal form of anemia commonly seen in people of Mediterranean descent. People with beta thalassemia major invariably require blood transfusions, which can eventually result in iron overload.¹¹ L-carnitine stabilizes red blood cells and supplementation may decrease the need for blood transfusions. In a preliminary study, children with beta thalassemia major who took 100 mg of L-carnitine per 2.2 pounds of body weight per day for three months had a significantly decreased need for blood transfusions.¹²