How do glucose levels affect the cognitive performance of patients with type 1 diabetes?

A new study shows that fluctuations in blood sugar levels can affect thinking skills in different ways in people with type 1 diabetes (T1D).

The researchers looked specifically at what is known as cognitive processing speed (how quickly people process incoming information) and attention.

The results of the study conducted by researchers at McLean Hospital and Washington State University, published in the journal npj Digital Medicine, show that perception was slower in moments when glucose was unusual, that is, much higher or lower than someone's usual glucose level.

However, some were more susceptible than others to cognitive effects due to glucose fluctuations.

Type 1 diabetes (T1D) is an autoimmune disease characterized by glucose dysregulation. Previous studies have shown that very low and very high glucose levels impair cognitive function. However, technological limitations have made it difficult to study the effect of naturally occurring glucose fluctuations on cognition outside the laboratory, preventing researchers from obtaining repeated, high-frequency measurements within the same individuals over time. High-frequency measurements are necessary to understand whether glucose fluctuations affect cognition similarly in everyone.

In the new study, researchers used digital glucose sensors and smartphone-based cognitive tests to collect glucose data and results of repeated tests in 200 individuals with type 1 diabetes.

Glucose data were collected every five minutes, while cognitive data were collected three times a day for fifteen days, while the participants went about their daily lives normally. This allowed the researchers to examine the cognitive impact of naturally occurring glucose fluctuation. With so many data points from each individual, they were able to use machine learning to test whether the effect of glucose on cognition differed from person to person.

The study showed that cognitive function is impaired when the glucose level is much higher or lower than normal, however, cognitive declines were only observed when it came to processing speed, not attention.

The researchers hypothesized that processing speed is affected by short-term, momentary fluctuations in glucose levels, while sustained attention is affected by high or low glucose levels that persist over longer periods of time.

The researchers also found that people differed in how much glucose fluctuations affected their cognitive speed, and that some people, including older adults and adults with certain health conditions, were more affected by glucose fluctuations than others.

“Our results show that people can differ greatly from each other in how their brains are affected by glucose,” said Laura Germain, co-lead author of the study and director of the Maclean’s Laboratory for Brain Technology and Cognitive Health. “We found that reducing glucose fluctuations in daily life is important for improving processing speed.” "This is especially true for people who are older or have other health conditions associated with diabetes."

One surprising finding was that people with type 1 diabetes tend to reach peak intellectual performance when their blood sugar levels are slightly above normal.

“This was an important finding because people with diabetes often feel better at a glucose level higher than what is considered healthy,” said Naomi Chaytor, co-lead author, professor and department chair at Washington State University.