Study finds normal blood sugar level may not be so sweet on the brain

A new Australian study suggests that sometimes normal isn’t necessarily optimal.

Canberra researchers found that blood sugar levels treading on the high side of what is considered to be normal could potentially cause the brain harm. A subject pool amassing 249 patients in their early 60s prompted the discovery of a dreaded tether between the shrinkage of two brain regions (the hippocampus and the amygdala) and blood sugar levels thought to be normal.

"It has been generally assumed that blood glucose in the normal range is not a risk factor for brain health in non-diabetics," researcher Nicolas Cherbuin, PhD, told WebMD. "If the present results are replicated in other studies the definition of normal fasting blood glucose levels and of diabetes may need to be re-evaluated."

For the study, each participant, equipped with normal blood sugar levels, underwent a set of brain scans — one at the onset of the trial and another four years later. By way of before-and-after image comparison, researchers observed a startling amount of brain shrinkage in individuals still within the standard range, just below the precipice of what the World Health Organization deems pre-diabetes. Even when overweight or obese partakers were excluded and the more staunch American Diabetes Association criteria was applied, researchers found the results to be unflinching.

Cherbuin characterized the results as “robust” and worthy of further investigation. For some medical constituents, the work completed by Cherbuin and his colleagues is yet another chapter in the developing saga detailing the damning pairing between diabetes and the brain.

“This in line with many other studies that have been published and adds to all of the data on diabetes affecting brain health,” said R. Scott Turner, MD, PhD — director of the Memory Disorders Program and a professor of neurology at Georgetown University Medical Center (who was not involved with this study) — in an interview with ABC News.

Even so, Cherbuin suggested that all individuals, regardless of diabetic status, should be wary: “These findings suggest that even for people who do not have diabetes, blood sugar levels could have an impact on brain health.”

As of now, factors involved in the regulation of blood sugar are still largely misunderstood. Because of this, certain experts are compelled to hold off on making sweeping diagnoses with the present amount of evidence.

"The research is too preliminary, and the association shown here does not establish a cause or mechanism," commented Marc Gordon, MD, chief of neurology at Zucker Hillside Hospital in Glen Oaks, N.Y., in the WebMD interview. "To speak as a clinician and tell patients that they better cut out all candy because it will shrink their brain is a leap of faith."

Gordon — in light of the work yet to be completed on the matter and in the shadow of what is already known about the importance of balanced diets — noted that when it comes to physicians prescribing behaviors, mother still knows best.

"It's just what all of our mothers told us: Eat well and exercise," he said. "That's a principle we would all do well to live by."

Next on the docket for defining the new normal, Cherbuin plans to investigate the impact brain changes and shrinkages may have on a patient. Cherbuin hopes the study findings will be simulated and the conceptualization of what is considered normal blood glucose levels will become more precise thereafter.

“If replicated, these findings may contribute to a reevaluation of the concept of normal blood glucose levels and the definition of diabetes,” Cherbuin concluded.

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