Glucose comes from the breakdown of food. It is the body's energy source. It can pass from the blood to cells with the help of a hormone called insulin . Without insulin, glucose will build up in the blood and cause hyperglycemia. At the same time, your body's cells are starved for glucose (energy).
A lack of insulin or a resistance to insulin causes diabetes. In type 2 diabetes the body is resistant to high levels of insulin. There is plenty of insulin in the body but the cells are unable to use it.
High blood sugar levels over a long period of time can damage vital organs. This can include the kidneys, eyes, and nerves.