Hyperglycemia causes damage in the blood vessels and nerves of the body, which in turn develop into the major complications of diabetes. Damage happens when excess glucose in the blood settles into the cells and forms a substance known as advanced glycation endproducts (AGEs). These accumulate over time.
AGEs are found in vessels of the eyes, kidneys and extremities. They also are found in other major blood vessels and lead to plaque formation and atherosclerosis, contributing to heart disease.

