The pancreas lies at the back of the abdomen and has two main functions:

to produce a juice that flows into the digestive system to help us digest food
to produce the hormone called insulin.

Insulin is the key hormone that controls the flow of glucose (sugar) in and out of the cells of the body.

Type 1 diabetes is caused by a lack of insulin output because of damage to the pancreas gland.

Damage to the pancreas can occur for a many reasons, eg a viral infection. But the most common cause in Type 1 diabetes is the body’s own immune system.

Insulin-producing cells in the pancreas of people with Type 1 diabetes are destroyed by cells that normally defend us from invading organisms.

Auto-immune diseases
There are other auto-immune diseases, for example of the thyroid gland.

They are more frequent in people who have Type 1 diabetes.

This may reflect an inherited tendency to developing auto-immune disease that is triggered by some other factor in the environment.

Exactly what that trigger can be is still unclear, but there is some evidence to suggest that a virus infection could start the process off.