Diabetes, also known as diabetes mellitus, is a chronic condition in which the body either produces no or insufficient insulin, or the insulin that is produced cannot be used effectively. Insulin is a hormone produced by the pancreas that regulates blood sugar levels by promoting the uptake of glucose into the cells of the body. There are three main types of diabetes: type 1 diabetes, type 2 diabetes and gestational diabetes. Type 1 diabetes occurs when the body's immune system destroys the cells in the pancreas that produce insulin. This leads to a lack of insulin in the body, which in turn increases blood sugar levels.