An insulin-dependent diabetic has a pancreas that is not making insulin or not making enough of it. Researchers now believe that this type of diabetes is an autoimmune disease, that is, a disease caused by an overreactive immune system. Although much is still unknown, medical scientists now think that some triggering factor confuses the body's defense system into attacking the beta cells of the pancreas and killing them. This autoimmune reaction may be triggered by a virus or by several viral infections.

Heredity and environment are other factors in the development of insulin-dependent diabetes. According to researchers, an immune system that will overreact and attack the beta cells is an inherited characteristic, but this overreaction still must be turned on by a triggering factor such as a virus.

White people who trace their heritage to Northern Europe have a higher incidence of insulin-dependent diabetes, but it is rarely seen in Orientals. Blacks and certain American Indian tribes have a high incidence of noninsulin-dependent diabetes.

The autoimmune destruction of the beta cells does not happen overnight. A person can get by quite well with less than a full amount of beta cells making insulin, but at some point, enough cells are destroyed so that a sufficient amount of insulin is no longer produced and the symptoms of diabetes start to appear.