A little or a lot! Diabetes mellitus is a disorder of glucose regulation. Glucose levels are too high. If this continues over long periods of time, the high glucose levels cause damage to your body (eyes, kidneys, nerves) and can increase the risk of atherosclerosis (heart attacks, strokes). If your diabetes remains well controlled (glucose levels near normal), you have much less risk of damage to your body.
Multiple. Diabetes can cause serious health complications including heart disease, stroke, blindness, kidney failure, neuropathy, and lower-extremity amputations. Diabetes is the seventh leading cause of death in the United States. for more info, go to this link: http://www.cdc.gov/diabetes/basics/diabetes.html.