L-Carnitine is an endogenous quaternary ammonium compound essential for fatty acid transport into the mitochondria for energy production. The L-isomer is biologically active and exhibits anti-osteoporotic, antioxidative, and cardioprotective properties. In clinical settings, L-Carnitine administration increases muscle carnitine content and work output while decreasing glycogen utilization during exercise. It also improves postprandial flow-mediated dilation, supporting vascular function. In animal models, L-Carnitine increases bone mineral density and decreases bone resorption. Additionally, it improves plasma markers of exercise stress and has shown benefits in cardiovascular disease, including reduced ventricular arrhythmias, decreased symptoms of angina, and lower mortality rates following myocardial infarction.