Each time blood glucose exceeds 140mg/dl, the most susceptible/sensitive/weak tissues that blood comes in contact with are the first to be damaged. Those tissues (which are made up of cells) could be anywhere in the body. Most obvious are blood vessels themselves. That's why diabetics experience cardiovascular disease.   Each time blood glucose spikes occur, a little more damage accumulates. If the body can't repair the damage, or repairs that do occur aren't effective, the net result is continued tissue/cell deterioration.   The good news: If blood glucose spikes over 140mg/dl are eliminated before significant damage has occurred, the body can often repair the damage over time.