Insulin is ahormone produced by the pancreatic islet of Langerhans cells that helps convert carbohydrates to the simple sugar glucose and regulates glucose levels in the blood. Its other functions include regulating specific events in a cell's life cycle. Insulin is best known for treatment of the metabolic disease diabetes mellitus.

The importance of glucose as an indicator of diabetes was noted for thousands of years by Asian and Middle Eastern physicians. In seventeenth century Europe, a sweet flavored urine was listed a symptom of diabetes. In 1815, the French chemist Michel Eugène Chevreul discovered that the sweetness came from "grape sugar" or glucose. Later in the nineteenth century scientists learned how the body manufactures, stores, and uses glucose.

Injury to the pancreas, a gland attached to the small intestine, was linked to diabetes beginning in the seventeenth century and confirmed by animal experiments in the late...