Diabetes and mental illness... chicken and egg?

So now they've found a link between diabetes and mental illness. "We know that people with diabetes have an increased incidence of mood and other psychiatric disorders," they say. I had no idea! I wouldn't think that an insulin disorder would have anything to do with a dopamine problem, but...

"...insulin -- the hormone that governs glucose metabolism in the body -- also regulates the brain's supply of dopamine -- a neurotransmitter with roles in motor activity, attention and reward. Disrupted dopamine signaling has been implicated in brain disorders including depression, Parkinson's disease, schizophrenia and attention-deficit hyperactivity disorder."

Huh. So your insulin levels actually help moderate your brain function. But of course, and this doesn't make sense, a lot of psychiatric drugs can cause diabetes. If insulin regulates brain disorders, why mess with insulin and cause people to become diabetic? This is the part that makes no sense to me.

There's a lot of diabetes in my family, and a lot of mental illness. I'll have to see which one came first.