Not only a connection between thiamin deficiency and diabetes, but also mitochondrial dysfunction, Alzheimer's, to name a few...

http://lpi.oregonstate.edu/infocenter/vitamins/thiamin/

Scroll down to the "Disease Prevention" (yes, it says prevention, not treatment) section and you see this under Diabetes:

:...In a randomized, double-blind pilot study, high-dose thiamin supplements (300 mg/day) were given for six weeks to hyperglycemic individuals (either glucose intolerant or newly diagnosed with type 2 diabetes). Thiamin supplementation prevented any further increase in fasting glucose and insulin levels compared with placebo treatment but did not reduce the hyperglycemia (36). However, one study suggested that thiamin supplementation might improve fasting glucose levels in type 2 diabetics in early stages of the disease (i.e., pre-diabetes or early diabetes) (37)...."

And under the "Disease Treatment" section they list Alzheimer's and have this to say, in part:

"...Thiamin deficiency has been linked to increased beta-amyloid production in cultured neuronal cells and to plaque formation in animal models (57, 58). These pathological hallmarks of AD could be reversed by thiamin supplementation, suggesting that thiamin could be protective in AD. Moreover, other disorders including mitochondrial dysfunction and chronic oxidative stress have been linked to both thiamin deficiency and AD pathogenesis and progression (9, 59). ..."

It seems that our ability to absorb nutrients from the gut declines with age naturally, which would explain why PD and Alz. used to be seen primarily in the elderly populations. http://www.jbc.org/content/142/1/239.full.pdf ("reduced function of the alimentary tract is a common attribute of thiamine deficiency...")

I am wondering whether, with with our lousy diet and rampant antibiotic use, we have wrecked our gut biome and ability to absorb critical nutrients, and thus see younger and more people suffering from the collective symptoms known as PD, dementia, Alz., etc. We know there is reduced glucose metabolism in Alz, it can actually be seen. Many brave scientists have been calling Alz. a third type of diabetes, a diabetes of the brain, and now it looks like more and more PD research is heading the same direction.