The mechanism here appears to be the metabolism of compounds in cinnamon into sodium benzoate, which we already knew was helpful with Parkinson's.
The mechanism behind cinnamon's effects on blood glucose, OTOH, seems not to be terribly well-studied, given a few minutes' searching. One paper I found says, "cinnamon enhances glucose uptake by activating the insulin receptor kinase activity, auto-phosphorylation of the insulin receptor, and glycogen synthase activity." [1] Otherwise, the literature seems all to be, "We observed this effect..."
