Insulin is a chemical messenger that allows cells to absorb glucose, a sugar, from the blood.
The pancreas is an organ behind the stomach that is the main source of insulin in the body. Clusters of cells in the pancreas called islets produce the hormone and determine the amount based on blood glucose levels in the body.
The higher the level of glucose (sugar), the more insulin goes into production to balance sugar levels in the blood.
Insulin also assists in breaking down fats or proteins for energy.
A delicate balance of insulin regulates blood sugar and many processes in the body. If insulin levels are too low or high, excessively high or low blood sugar can start to cause symptoms. If a state of low or high blood sugar continues, serious health problems might start to develop.
Source: WebMD