Diabetes is a group of chronic diseases of the endocrine system in which the body either does not produce enough insulin or cannot use it effectively, which leads to a persistent increase in blood glucose (sugar) levels (hyperglycemia). The main types are type 1 (lack of insulin) and type 2 (insulin resistance). Symptoms include thirst, frequent urination, weakness, and diabetes can cause complications for the heart, kidneys, eyes, and nerves.