Too high or too low glucose levels may slow cognition in people with type 1 diabetes


  • Type 1 diabetes is an autoimmune disease that affects the pancreas and insulin production.
  • Previous studies show that people with type 1 diabetes are at an increased risk for several health conditions, including eye problems and heart disease.
  • Researchers from McLean Hospital believe the naturally occurring glucose level fluctuations in people with type 1 diabetes may also affect their cognitive function, which could impact Alzheimer’s disease risk.

As of 2021, about 8.4 million peopleTrusted Source around the world had type 1 diabetes. Researchers project this number will increase by approximately 500,000 new cases every year, with a worldwide projection as high as 17.4 million individuals with type 1 diabetes by 2040.

Unlike type 2 diabetes, type 1 diabetes is an autoimmune diseaseTrusted Source for which there is currently no cure. This type of diabetes negatively affects the pancreas so that it can no longer produce enough insulin — a hormone that helps the body manage its blood sugar levels.

Previous studies show that people with type 1 diabetes are at an increased risk for several health conditions including cardiovascular diseaseTrusted Source, nerve damageTrusted Source, eye problemsTrusted Source, and cognition issuesTrusted Source.

Now, researchers from McLean Hospital — a member of Mass General Brigham — believe the naturally occurring glucose level fluctuations in people with type 1 diabetes may impact how well their brains work.

The study was recently published in the journal npj Digital MedicineTrusted Source.

How does type 1 diabetes affect the brain?

According to Dr. Zoë Hawks, director of the Computational Modeling & Cognitive Dynamics Program at McLean Hospital, instructor in psychiatry at Harvard Medical School, and lead author of this study, doctors and researchers need to have a better understanding of how type 1 diabetes affects the brain.

“Individuals with type 1 diabetes are at increased risk for cognitive impairment, and cognitive variability is an important indicator of long-term brain health,” Dr. Hawks explained to Medical News Today. “Understanding how glucose impacts cognitive variability in the context of clinical risk factors — for example, microvascular complications — may support the development of new tools to evaluate and monitor brain health in type 1 diabetes.”

Past studies have linked type 1 diabetes to cognitive issues. For example, a study published in March 2022 discovered that older adults with type 1 diabetes had significantly poorer cognitionTrusted Source compared to those with type 2 diabetes or without diabetes.

Research published in November 2018 found that older adults with type 1 diabetes who had suboptimal or poorTrusted Source glycemic control of diabetes were at an increased risk for dementia.

A study published in July 2021 reported that severe hypoglycemic and hyperglycemic eventsTrusted Sourceincreased dementia risk in older adults with type 1 diabetes.

Glucose’s effect on brain processing speed

For this study, Dr. Hawks and her team recruited 200 people with type 1 diabetes who used digital glucose sensors and smartphone-based cognitive tests to collect glucose level and cognition data three times a day for 15 days.

“Type 1 diabetes is characterized by elevated glucose and increased glucose variability,” Dr. Hawks said.

“Previous laboratory studies have shown that extreme glucose levels impair cognition. However, due to technological limitations, it’s historically been difficult to study the impact of glucose on cognition outside of the laboratory. We were interested in using new, remote data collection technologies to understand how glucose impacts cognition in everyday life and whether this effect differs from person to person,” she explained.

When analyzing the collected data, scientists found that the cognitive function of processing speed — how quickly the brain receives, processes, and responds to received information — was impaired when a person’s glucose levels were either considerably higher or lower than usual. However, this was not true for another cognitive function called sustained attention — the ability to focus on a specific task for a long time.

“This finding was unexpected, but not altogether surprising,” Dr. Hawks said.

“It may reflect the fact that glycemic variability impacts sustained attention and processing speed on different timescales. For example, recent work by Pyatak and colleagues suggests that sustained attention varies in relation to longer-term effects of glucose — e.g., over hours, days — whereas we found that processing speed is sensitive to current glycemic status,” she said.

Peak cognitive performance with higher glucose levels

Study researchers also discovered that a study participant’s peak cognitive performance coincided with glucose levels being slightly higher than their usual range. However, their performance dropped if their glucose levels continued to rise.


“This was surprising. We know high glucose is bad for long-term brain functioning and cognitive health, but it looks like — at least in the short term — having glucose that is moderately high is associated with faster thinking and response times in people with type 1 diabetes.”
— Dr. Zoë Hawks


“This is important for patients to know because it means that if someone is working hard to lower their blood glucose (to) a healthier range, they might notice that their thinking is a little slower than usual. We expect that these are short-term effects as their body adjusts to a lower glucose level. People with higher average glucose had slower average thinking speed than people with lower average glucose,” Dr. Hawks explained.

Dr. Hawks said there are two big takeaways from this study that medical professionals should be aware of.

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