I have a friend who was recently diagnosed with type 1 diabetes. Why do people with diabetes heal so poorly after a injury?

In your friend’s case, I rather doubt that any slow healing is due to her diabetes. In older people however, who have had diabetes for many years, and especially when blood sugar levels have been poorly controlled, small blood vessels become damaged and this does interfere with the repair process.

DOB
Additional comments from Dr. Stuart Brink:

Only people with diabetes whose glucose control is inadequate have problems healing well. If one is in reasonable glucose control and circulation is not impaired, then there should be no reason to have any healing problems at all. Smoking, high lipid levels, hypertension and drug abuse are also associated with poor circulation — and thus poor wound healing.

SB