Diabetes and the Brain

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It’s hard enough managing diabetes when you have all your mental faculties, right? Well, for a lot of people, it’s worse. They have diabetes and mental illness, too.

Web editor Tara Dairman put me on to this story after a reader asked about it, and it turned out to be interesting enough to share.

Are mental illness and diabetes linked?
According to The New York Times, “among the mentally ill, roughly one in every five people appear to develop diabetes—about double the rate of the general population.”

The reverse also appears to be true. Research has found that as many as one in five children with newly diagnosed Type 2 diabetes (now there’s a depressing phrase) may also have a neuropsychiatric disorder.

The illnesses include depression, attention deficit hyperactivity disorder (ADHD), autism, developmental delay, schizophrenia, and bipolar disorder. The research suggests that children with a neuropsychiatric disease may be at risk for Type 2 diabetes, and vice versa. At the other end of life, Alzheimer disease has also been linked with diabetes and other insulin problems. But why?

What’s the connection?
Some people blame the meds that people with serious mental illness receive. They tend to cause major weight gain which could trigger Type 2 diabetes. Others say that depression contributes to diabetes by making people sedentary. But that doesn’t explain the bipolar disorder, schizophrenia, Alzheimer disease, and the others. It may well be that insulin plays a major role in brain function. When insulin processing is damaged, psychiatric problems can result.

An article by science writer Scott Allen reports on recent research showing that Alzheimer disease and schizophrenia, two of the most challenging mental illnesses, “could be secondary to a breakdown in the way brain cells process insulin.” Researchers are throwing around terms like “Type 3 diabetes” and “diabetes of the brain” to describe these conditions.

Whether an insulin shortage “causes [schizophrenia], contributes to the disease, or it’s the brain’s response to injury, we don’t know yet,” said Jesse Roth, M.D., F.A.C.P., geriatrician-in-chief of the North Shore–Long Island Jewish Health System in New York, who has studied insulin’s role in the brain since the 1980’s.

According to Allen, “Dr. C. Ronald Kahn, president of the Joslin Diabetes Center in Massachusetts…suggests that insulin problems in the brain may, in turn, make people more vulnerable to Type 2 diabetes.” Lab mice modified to block insulin processing in the brain became obese and showed signs of diabetic insulin resistance.

Insulin as brain therapy
For a while, doctors were treating schizophrenia by putting people into insulin shock. Some, such as John Nash, Jr., the mathematician portrayed in the movie “A Beautiful Mind,” actually benefited, but up to 10% of the patients died, and by the early 1960’s the treatment had been stopped.

In 2005, researchers at Psychiatric Genomics discovered that the same 14 genes that are missing in the brains of people with schizophrenia are also missing in muscle tissue of people with diabetes. In the lab, they were able to increase the availability of those genes by giving insulin, which could lead to new therapies for schizophrenia.

Other scientists are studying whether inhaled insulin improves memory in people with Alzheimer disease.

I don’t know that any of this information helps people deal with diabetes. But it does give a glimpse into how incredibly complicated our bodies are, and how important insulin function is, and how our brains and bodies might be connected. And the probable association between Type 2 and later mental illness gives us another reason to help children and families avoid diabetes in the first place.

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