Type 1 diabetes occurs when specialized cells called beta cells found in the pancreas – an organ located behind the stomach – are destroyed. These cells normally exist in clusters in the pancreas called the Islets of Langerhans and function to make and release the hormone insulin; without them, the body is incapable of producing any insulin.

When someone without diabetes eats a meal, the nutrients are absorbed into the bloodstream by the digestive tract. This causes a rise in blood sugar which signals the beta cells of the pancreas to release insulin. Insulin travels in the bloodstream and signals the cells of the body to take up sugar from the blood and use it as their primary source of energy. It also signals certain cells to store excess sugar for later use.

When the beta cells are destroyed and the source of insulin is lost, this system can no longer function. Instead, after a meal, the blood sugar level rises but there is no signal telling cells to take up that sugar. Two things happen as a result: blood sugar levels stay high, and the cells starve for want of energy. These factors lead directly to the early symptoms experienced by untreated diabetics: high blood sugar levels are eliminated in the urine, leading to frequent urination and excessive thirst to replace lost fluids; because cells cannot get enough energy, you feel hungry all the time but actually lose weight, and you feel lethargic and fatigue easily.

While it is clear that the loss of the pancreatic beta cells is the cause of type 1 diabetes, the reason these cells die is less clear. Researchers believe that the body’s immune system mistakenly attacks the beta cells leading to their demise. Approximately 85% of patients have antibodies in their blood that are directed against islet cells. Thus, type 1 diabetes is an autoimmune disease, a type of disease that occurs when the immune system attacks normal body cells. The reason that the immune system goes awry in type 1 diabetes is unknown, as it is with other types of autoimmune diseases. Researchers believe genetics may play an important role in the development of type 1 diabetes. Environmental conditions such as exposure to certain viruses may also play a role.