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Diabetes Health Center

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High Blood Sugar Levels and Dementia Risk

Elevated blood glucose may harm the brain, even in people without diabetes, researchers say


All study participants were aged 65 and older and free of dementia at the start of the study. Everyone had had at least five blood sugar checks in the two years prior to study enrollment.

At the start of the study, 232 people had diabetes, while 1,835 did not.

Through detailed health records kept on each participant, the researchers were able to estimate each person's average glucose levels.

Over the next seven years, on average, one-quarter of the participants developed dementia, including 450 who did not have diabetes and 74 with diabetes. About 20 percent of them had probable Alzheimer's disease, the most common form of dementia, while roughly 3 percent had dementia from vascular disease and slightly more than 3 percent were deemed to have dementia from other causes.

When researchers compared participants' average blood glucose levels to their risk of dementia, they found that for people without diabetes, as glucose levels rose above 100 milligrams per deciliter (mg/dL), dementia risk increased, too.

People with average daily blood sugars of 105 to 115 mg/dL in the previous five years saw a 10 percent to 18 percent increase in the risk of developing dementia.

For people with diabetes, the risk began to rise with average blood sugars above 160 mg/dL. People with diabetes had a 40 percent greater risk of developing dementia if their average blood sugars were above 190 mg/dL for the same time frame.

The increased risk remained even after researchers adjusted their results to account for other factors, such as smoking, inactivity or heart disease, that might have skewed the results.

Study author Dr. Paul Crane, an associate professor of medicine at the University of Washington in Seattle, agreed the risk isn't monumental. "It's not explaining boatloads of dementia risk," he said.

And because the study only looked at the relationship between blood glucose and dementia, it can't definitively say that higher blood sugar levels lead to memory loss, or that lowering blood sugar can reduce a person's risk.

"People who had lower blood sugar had lower risk than people who had higher blood sugar," Crane said. "That's not the same thing as saying that lowering your own blood sugar through any means has any influence on your personal risk of dementia," he added.

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