Co-Enzyme Q-10, or Co-Q-10 for short, is a natural compound which is made by your body and stored in the mitochondria of each and every cell. The highest concentrations tend to be found in the liver, kidneys, heart and lungs, and it is thought that this vitamin like substance has many different roles to play. Your natural production of Co-Q-10 decreases with age, which is why some people choose a top-up with a supplement.