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Type 2 diabetes diminishes mental performance, but how?

Losing keys and forgetting names are real enough worries for anyone growing older. But for those with Type 2 diabetes, the prospect of cognitive decline is very real. Those who develop the metabolic disorder have a roughly 75% higher risk of developing some form of dementia than do those without the metabolic disorder.

Underscoring that reality, new research suggests that insulin resistance and elevated levels of sugar in the blood — both hallmarks of Type 2 diabetes — unleash a cascade of events that, over time, impair the brain's blood vessels.

With remarkable speed — over two years during which researchers tracked a group of older adults with diabetes — those changes can sap the brain's ability to react flexibly to daily mental challenges.

The new research, led by neurologists at Beth Israel Deaconess Medical Center in Boston and published in the journal Neurology, was published Wednesday.

In a group of 40 study participants ranging from 50 to 85 years old, brain scans showed the 19 who had Type 2 diabetes had more constricted blood vessels throughout their brains than did their peers who did not have diabetes. The differences were slight, but evident, at the study's outset. After two years, they were much more pronounced.

The vasculature in the brains of diabetics and a healthy comparison group looked and behaved differently as well. Both at the study's start and more noticeably after two years, blood vessels in the diabetics' brains showed less ability to expand and contract to accommodate changing mental tasks.

Not surprisingly, the diabetics had less brain volume too — an indication that the process of atrophy had already begun.

Subjects with Type 2 diabetes also performed worse, on average, in tests of memory, learning, complex reasoning and daily functioning than did subjects without diabetes.

Upon their recruitment into the study, the mental performance of subjects with diabetes was considered normal. But it was lower than that of healthy controls of the same age. After two years, the non-diabetic controls showed few signs of mental slippage. But in all but one measure — verbal fluency — the cognitive performance of those with Type 2 diabetes had declined markedly, and differences between the two groups had widened.

The worrisome changes in blood flow to the brain were most pronounced in diabetic subjects who showed higher initial levels of inflammation, the study showed. And the worrisome changes in mental functioning were most pronounced in those subjects whose glycemic control was poorest as they entered the study.

Many factors contribute to cognitive decline in those with diabetes, the study authors said. But these findings strengthen the argument that both inflammation and damage to blood vessels in the brain play a role in sapping brainpower.

And they may help explain preliminary results suggesting how statins (used to lower cholesterol), anti-inflammatory drugs (used for pain) and beta-blockers (which reduce wear and tear on blood bessels throughout the body) might prevent or slow dementia.

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