• Researchers say higher blood sugar levels can affect brain health and lead to cognitive decline.
• They say people with diabetes as well as prediabetes face these risks.
• Higher blood sugar levels can cause inflammation that can result in cognitive decline, experts say.

High blood sugar could put you at higher risk of cognitive decline and dementia even if you don’t have fully developed diabetes.

Lower levels of blood sugar, on the other hand, are associated with better brain health, according to a new study from researchers at University College London and the London School of Hygiene & Tropical Medicine.

The study, published in the journal Diabetes, Obesity and Metabolism, suggests that keeping blood sugar in the normal range is important for preventing cognitive decline and dementia.

The researchers reported that people diagnosed with prediabetes — generally defined as having A1C levels of 5.7 to 6.4 percent — are 54 percent more likely to develop vascular dementia than people with normal blood sugar levels (less than 5.7 percent).

That’s lower than the threefold risk of vascular dementia among people with diabetes (A1C of 6.5 percent or higher), but it’s still significant, said Victoria Garfield, PhD, the lead study author and a research fellow in genetic epidemiology at University College London’s Institute of Cardiovascular Science. 

“Based on previous research and now our own findings… we can certainly say that prediabetes is a high-risk state for people to be in and that we now know that it is certainly associated with greater risk of cognitive decline and vascular dementia, in particular,” Garfield told Healthline.

Knowing the risks

Garfield said that researchers have “known for a long time that individuals with diagnosed diabetes are, for several complex reasons that we still do not fully understand, more likely to have worse brain health in older age.”

But the study highlights the brain damage that can result from any sustained elevation in blood sugar levels.

“This is further supported by our data, which showed that those in the prediabetes state are also more likely to have a smaller hippocampus and greater volume of white matter hyperintensities on their brain scans — the latter being a measure of vascular brain damage,” Garfield said.

People with prediabetes also performed more poorly on cognitive function tests than those with normal blood sugar, she noted.

James Giordano, PhD, a professor in the departments of neurology and biochemistry and chief of the Neuroethics Studies Program at Georgetown University Medical Center’s Pellegrino Center for Clinical Bioethics in Washington, D.C., told Healthline that prediabetic people may actually be at greater long-term risk than those who have been diagnosed with diabetes.

“Prediabetic people are often not under therapeutic care and walk around with levels of blood sugar that are problematic but not controlled,” he said.

Damage from inflammation

Giordano said that high blood sugar levels — even those that are episodic and not chronic — cause sugar metabolites to accumulate in brain cells, resulting in systemic inflammation.

“These oxidative metabolites cause damage to cell membranes like crazy,” Giordano said.

Over time, this low-grade chronic systemic inflammation results in what is referred to as “inflammaging,” which can accelerate the biological aging process and worsen age-related diseases, including vascular conditions.

“In the brain, blood vessels become tight, rigid, and leak chemicals that also are inflammatory,” degrading blood flow and creating a feedback loop of inflammation, Giordano said. “You begin to see areas of cell death due to increased oxidative damage and hypoxia,” or oxygen starvation.

This, in turn, can lead to a decline in cognitive processing and vascular dementia.

“If you see your A1C numbers creeping up and it remains elevated, it’s actually a yellow flag if not a red flag,” Giordano said. 

Garfield cautions that her study is observational, doesn’t establish a causal link between prediabetes and brain damage, and requires replication in future studies.

However, she said, “our findings definitely open up questions about potential benefits of diabetes screening in the population and whether earlier intervention should be considered.”

The research also highlights the importance of monitoring blood sugar levels in order to intervene early to prevent damage to the brain, which  sometimes can be irreversible.

“Individuals with prediabetes can reduce their risk of developing diabetes by having a healthy, balanced diet, being more active, getting good sleep, and maintaining a healthy weight,” Garfield said.

 

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