Why do many diabetics suffer nerve damage in their extremities?

Peripheral neuropathy is a major cause of foot ulcers that can lead to amputation in some people with poorly controlled diabetes. It's caused by nerve damage due to excess blood glucose.

When glucose gets inside your nerve cells, that causes big molecules to be built (sorbitol is one, for you crossword whizzes). Not only can't these get out of cells easily, but they attract water to those cells, causing them to get bigger. Big cells may be good for prisoners, but not for your body. Why?

Those big nerve cells get compressed by the tight myelin sheath that surrounds them (kind of like trying to put more tomatoes in that little bitty can—the tomatoes break apart), eventually damaging those nerves. That's the long-nerve dysfunction that diabetics often get, when they aren't able to sense their feet normally. This is called stocking-glove nerve dysfunction; you lose sensation in all areas covered by a stocking or glove.

Not only can this lead to ulcers and tissue damage, but it can also lead to injury. If you can't feel your feet, you're more likely to injure them and then get infections in the injury.