Diabetes develops when insulin loses its ability to transport sugar from the bloodstream to the body’s cells. Insulin resistance occurs when the pancreas is unable to produce enough insulin to remove blood sugar from the body and transport it elsewhere. Type 1 diabetes develops when the immune system mistakenly destroys insulin-producing cells in the pancreas. Type 2 diabetes symptoms often appear gradually. Among the symptoms are increased thirst, frequent urination, blurred vision, and slow healing.