People who cannot make insulin in their bodies, or who make it but their body cannot use it properly, have the disease diabetes. When blood glucose levels fall below a certain level, the human body begins to use stored sugar as an energy source through glycogenolysis. This process breaks down the glycogen stored in the liver and muscles into glucose which can then be used as an energy source. Insulin is a central metabolic control mechanism. Insulin is also used as a control signal to other body systems (such as amino acid uptake by body cells). In addition, it has several other anabolic effects throughout the body. Insulin affects vascular compliance and cognition.