High Blood Sugar and Cognitive Decline in Teens

High Blood Sugar and Cognitive Decline in Teens

You may have heard that high blood sugars can make your feel slow, fuzzy or tired. Perhaps you’ve experienced it yourself. The research suggests that this weary, leaden feeling could be more than just an annoyance or an inconvenience. It could well indicate a very real and serious degree of cognitive impairment.

The short-term woes of hyperglycemia are an under-discussed issue in the world of diabetes. We all know about the single worst consequence of acute hyperglycemia, diabetic ketoacidosis, a potentially deadly condition that occurs primarily in patients with Type 1 diabetes. We also know all about the long-term dangers of chronic hyperglycemia—neuropathy, blindness, kidney damage, heart disease, and so on—that effect patients of both types.

But we spend relatively little time discussing how bad high blood sugars can feel in the moment. Kerri Sparling, a popular diabetes blogger, once described high blood sugar as “a thick feeling in the base of your brain, like someone’s cracked open your head and replaced your gray matter with sticky jam.  I find myself zoning out and staring at things, and my eyeballs feel dry and like they’re tethered to my head by frayed ropes instead of optic nerves.  Everything is slow and heavy and whipped with heavy cream.”

Anyone familiar with these sensations will be unsurprised to read the conclusions of a new study published in Diabetes Care that attempted to evaluate the effect of transient high blood sugars on cognitive ability. The authors of the study, titled “Acute Hyperglycemia and Spatial Working Memory in Adolescents With Type 1 Diabetes,” found that blood sugars over 270 mg/dL “significantly reduced spatial working memory capacity.”

In the experiment, performed in Slovenia, twenty adolescents with Type 1 diabetes were given two different spatial working memory tests. During the first test, the youths exhibited normal blood sugars, an average of 137 mg/dL. During the second test, doctors administered a hyperglycemic clamp, and the adolescents’ blood sugar averaged 362 mg/dL. Meanwhile, a control group of non-diabetic adolescents took the same two tests. As might be expected, the kids in the control group got better at the test the second time around. But the children with Type 1 diabetes, subjected to acute hyperglycemia, got much worse. Brain scans confirmed the picture: in the healthy control group, brain activity increased when seeing the test for the second time; in the diabetic group, brain activity decreased.

Spatial working memory refers to the brain’s ability to temporarily store and understand spatial relationships; consider navigating through a new city, or trying to solve a Rubik’s cube. Good spatial working memory is highly correlated with academic performance, especially in mathematics, and is critical in innumerable everyday tasks and skills.

The negative consequences of this study should be obvious. Any one bout of acute hyperglycemia can meaningfully decrease the thinking ability of a person with diabetes, and could perhaps have a notable negative effect on test-taking, puzzle solving, job performance, and any other mental exercise. One can only assume that, in the case of chronic acute hyperglycemia, the results of persistent cognitive impairment could multiply and represent a serious impediment to living up to one’s potential.

High blood sugar is obviously harmful enough that the study raises a difficult question: was this experiment actually ethical? There is no question that acute hyperglycemia is unhealthy; that fact is central to everything we know about diabetes. The publication of the study touched off something of an outcry in the low-carbohydrate community:




Unfortunately, the presence of acute hyperglycemia is so commonplace that this study design—in which participants were required to suffer high blood sugars for only two hours—must not have raised raise any red flags during the ethical review that all studies undergo.

That this study design didn’t register as ethically problematic is arguably a very disturbing commentary on the state of diabetes care and the medical establishment’s tolerance of unhealthy blood sugars.

The sad fact of the matter is that a blood sugar level of 270-450 mg/dL is frighteningly common. According to the CDC, 9.9% of American adults with diagnosed diabetes have an A1c greater than 10.0%; among Type 1 teens, traditionally the group with the worst blood sugar control, the prevalence is likely far greater. An A1c of 10.0% indicates an average blood sugar of 279 mg/dL, near the bottom end of the range used in the study; anyone at this level is likely to spend many hours of every day experiencing this degree of acute hyperglycemia. Realistically, even many of those with better control—only 50% of adults with diabetes meet the American Diabetes Association’s target of <7.0%—likely struggle with acute hyperglycemia with regularity. Going into the study, the adolescent participants had an average A1c of 7.8%. For these kids, like most with diabetes of the same age, acute hyperglycemia was probably already a nearly everyday occurrence.

This is only the latest experiment to have associated hyperglycemia with deteriorating brain function. Other studies have found that “during acute hyperglycemia, cognitive function was impaired and mood state deteriorated,” that “chronic hyperglycemia may be detrimental to the developing brain,” and that “hyperglycemia … is toxic for the brain at any stage of life.” While the measurement of intelligence is fraught with challenges, and the magnitude of these effects may be difficult to pinpoint, these findings should be of concern to anyone in the diabetes community.

To what degree might a persistently impaired mental state contribute to the psychological and emotional issues that people with diabetes are so vulnerable to? Patients with diabetes are significantly more likely to experience depression, high levels of stress, anxiety, and other mental health issues, and some of those issues have unsurprisingly been found to correlate with increased blood sugar. That heavy and slow hyperglycemic feeling – “like someone’s cracked open your head and replaced your gray matter with sticky jam” – is a warning that should be taken very seriously.

Ross Wollen
Ross Wollen

Ross Wollen is a chef and writer based in Maine's Midcoast region. Before moving East, Ross was a veteran of the Bay Area restaurant and artisanal food scenes; he has also worked as a food safety consultant. As executive chef of Belcampo Meat Co., Ross helped launch the bone broth craze. Since his diagnosis with Type 1 diabetes in 2017, he has focused on exploring the potential of naturally low-carb cooking. Follow Ross on Twitter: @RossWollen

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