Nerve damage (Diabetic Neuropathy) in Diabetes. Excessive sugar (glucose) in the blood can injure of the tiny blood vessels (capillaries) that nourish nerves, especially in legsand feet. This can cause tingling, numbness, or a burning or pain that usually begins at the tips of the toes or fingers and gradually spreads upward. Left untreated, this result in loss all sense of feeling in the affected limbs. Damage to the nerves related to the alimentary canal (stomach and intestine) can cause problems like nausea, vomiting, diarrhea or constipation. Erectile dysfunction(impotence) can occur in men.