I also think the LOW blood sugars that occur in diabetics and those with insulin resistance are problematic too.

It has been noted recently that one episode of very low blood sugar in diabetics (which can be very common) is enough to accelerate Alzheimer's risk.

http://www.dailymail.co.uk/health/ar...ing-brain.html
This study above illustrates the glucose problem. Good blood flow with low sugar in it, would be a factor too.

Here is another about hypoglycemia:
http://www.medicalnewstoday.com/articles/146021.php

I imagine all nerves suffer when glucose gets too low.

When blood sugar is high, that means the cells are not getting any either, since the mechanism of transport seems to be not working (or insulin is missing).
Also the damage to peripheral nerves can be due to sorbitol being formed in the periphery.
http://en.wikipedia.org/wiki/Diabetic_neuropathy

I think we see in the ACCORD program, where the aggressive arm was closed early because of DEATHS, that keeping glucose TOO LOW or trying to keep the HbA1C around 6 (and under 7) led to death in that study. The total results have not been published yet, and when they are, it should be very revealing. The ACCORD study was about diabetics and glucose control. The other patients were allowed HbA1C of 7 after the more aggressive arm (group) was closed.

Keeping elderly patients at levels that are considered "normal" for non-elderly patients, may be a huge mistake, and lead to all sorts of pathology and loss of quality of life, and perhaps even death to some!