Linus Pauling did research this, and postulated that there was a significant evolutionary shift away from vitamin c and a replacement by APO(a) as the primary fuel for the metabolic furnace. This was enhanced by enzyme changes to favour fructose as a source of energy and storage. This shift seems to have occurred in early primates, before humans walked the earth.
Its been such a long time, and I suspect most of us do not miss it. It is a sugar oxidase enzyme, but we have plenty others to bother about. Not sure how it is connected to diabetes, though. Most animals ( apart from humans, some primates, guinea pigs and fruit bats) can synthesize vitamin c from glucose and indeed animal livers are a good source of vitamin c.