Carnitine helps the body convert fatty acids into energy, which is used for muscular activities throughout the body, including the heart muscle. The body produces carnitine in the liver and kidneys and stores it in the skeletal muscles, heart, brain, and sperm. Some people cannot properly absorb this nutrient from foods they eat. Carnitine deficiencies may be caused by genetic disorders, liver or kidney problems, high-fat diets, certain medications, and low dietary levels of the amino acids lysine and methionine (substances needed to make carnitine). In several studies, people who took L-carnitine supplements had a significant lowering of their total cholesterol and triglycerides, and an increase in their HDL ("good") cholesterol levels. Decreased blood flow to the legs from atherosclerosis (plaque buildup) often causes an aching or cramping pain in the legs while walking or exercising. This pain is called intermittent claudication and the diminished blood flow to the legs is called Peripheral Vascular Disease (PVD). At least one well-designed study suggests that carnitine supplements may improve muscle function and exercise capacity in those with PVD.