Glucose Changes in Type 1 Diabetes May Affect Thinking Speed

Endocrinology > Type 1 Diabetes — Some T1D patients showed very different responses to the same glucose level

by Kristen Monaco, Senior Staff Writer, MedPage Today March 19, 2024

In type 1 diabetes, glucose fluctuations were linked with cognitive processing speed, but not sustained attention, researchers reported.

According to data collected every 5 minutes from continuous glucose monitors, large fluctuations in glucose were associated with slower processing speed as measured by digital symptom matching reaction time, Zoë Hawks, PhD, of McLean Hospital in Belmont, Massachusetts, and colleagues found.

This link was significant across three different ecological momentary assessment completion cutoffs for digital symptom matching reaction time (≥50%, ≥66%, and ≥80%), they detailed in npj Digital Medicine.

Glucose fluctuations were not associated with sustained attention, as measured by gradual onset continuous performance test.

"We don't think that large glucose fluctuations are healthy for the body, but our results additionally suggest that when your glucose is much different from what your body is used to, you might find that your thinking is slower or more sluggish," co-author Laura Germine, PhD, of the McLean Institute for Technology in Psychiatry, explained to MedPage Today. "Maintaining stable glucose is important for overall health and will likely result in more stable cognitive function as well from hour to hour and day to day."

There were also individual differences when it came to cognitive vulnerability to glucose fluctuations, showing they may impact some more than others.

"Although most patients had slower thinking speed when their glucose was low or very high, people differed a lot in how much their thinking was impacted by changes in glucose," Germine added. "For some people, everyday changes in glucose made them noticeably slower in how quickly they could respond. For other people, these same changes in glucose didn't make a huge difference."

For example, when glucose was one standard deviation below its average, patients with a high vulnerability to glucose fluctuations responded 0.76 ms and 3.24 ms slower on gradual onset continuous performance test and digital symptom matching reaction times, respectively, than those with low vulnerability. Likewise, when glucose was two standard deviations below its mean, patients with high vulnerability to glucose fluctuations responded 1.8 ms and 9.30 ms slower reaction time on the two tests, respectively, than those with low vulnerability.

Germine said clinicians should be aware that patients can have very different responses to the same glucose level and that the same glucose level may be associated with thinking difficulties for one patient but not another.

Overall, participants consistently scored their fastest digital symbol matching reaction time when glucose levels were slightly higher than their individual average level. The fastest performance on average occurred at 0.72 standard deviations (47.49 mg/dL) above an individual's own glucose mean and was associated with 0.57% (5.30 ms) performance gain, relative to their cognitive averages.

"This was an important finding because people with diabetes often report feeling better at a glucose level that is higher than what is considered healthy," co-author Naomi Chaytor, PhD, of Washington State University in Spokane, said in a statement.

"It could be that your brain habituates to a glucose level that it is used to," Chaytor pointed out. "So a next step in this research is to see whether the glucose level associated with peak performance shifts down into the normal range when the amount of time spent above range is reduced, which can be achieved through use of automated diabetes management systems."

In a post-hoc analysis, neck circumference popped up as an unexpected variable that impacted the link between individual differences in cognitive vulnerability to glucose fluctuations. According to correlation tests, sleep apnea risk (r=0.43, P<0.001) and upper body adiposity (r=0.16, P=0.051) were linked with individual estimates of cognitive vulnerability to glucose fluctuations, while gender wasn't (r=0.11, P=0.17).

The study included 200 adults with type 1 diabetes and an average age of about 46 years. A little over half were female, average HbA1c was 7.5%, and glucose was 182.3 mg/dL. According to continuous glucose measures, glucose was in target range (70-180 mg/dL) on average 54.6% of the time and was above 180 mg/dL 42.5% of the time.

For the digital symbol matching test, patients were presented with a target-symbol and a digit-symbol pairing key and used a touchscreen to press the digit that was paired with the target symbol in the key. Each ecological momentary assessment session lasted 30 seconds. For the gradual onset continuous performance test, patients viewed a circular, grayscale image of a city or mountain and were instructed to press their touchscreen device when the image depicted a city and withhold a response when the image depicted a mountain. Each session lasted 60 seconds and consisted of 75 trials.