Cardiovascular disease is one of the major complications of diabetes, with both type 1 and type 2 diabetes linked to a higher risk of problems with your heart and blood vessels. One particularly dangerous type of cardiovascular event is a stroke, in which a clot (blockage) or, less commonly, a hemorrhage (bleed) prevents part of your brain from getting the blood it needs, resulting in damage to brain tissue. People with diabetes are about 1.5 times as likely to have a stroke as others, according to the American Diabetes Association.
Not everyone with diabetes has the same level of elevated stroke risk, of course. A number of factors — including blood glucose control, blood pressure, diet, and exercise — can affect how likely you are to have a stroke.
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A severe stroke can be deadly, but strokes that cause less damage can still result in ongoing symptoms like movement or speech problems, pain or numbness, and problems with thinking or emotions. While all of these symptoms can be disturbing, cognitive symptoms — those related to thinking — can be especially damaging to quality of life for many stroke survivors. And so researchers are interested in what factors can influence how much cognitive damage a stroke causes.
In a new study presented at the Endocrine Society’s virtual ENDO 2020 meeting, researchers at Tel Aviv University in Israel looked at 942 participants with type 2 diabetes who had a common type of stroke (called a lacunar stroke). Participants were given a test of mental performance called the Cognitive Assessment Screening Instrument (CASI) both as soon as possible after their stroke, and then periodically as they recovered.
The researchers found that having a higher HbA1c level (a measure of long-term blood glucose control) at the time of the first cognitive assessment was related to a greater reduction in cognitive function, with participants’ CASI score — measured on a scale of 0 to 100 — dropping by 0.06 points, on average, for every 1% increase in HbA1c. Even in later cognitive assessments as participants recovered, the first HbA1c measurement after their stroke was associated with lower cognitive performance over time.
What’s more, participants whose HbA1c increased during the follow-up period saw a further reduction in cognitive performance, with every 1% increase in HbA1c associated with a CASI score drop of 0.02 points in later cognitive assessments. While these drops might not seem enormous on a scale of 0 to 100, all of them were statistically significant — and remained so even after researchers adjusted for factors like age, sex, race, education level and other health issues like depression, high blood pressure, diabetic eye or kidney disease, and insulin use.
There could be a few different explanations for the link between HbA1c and cognitive function after a stroke, as noted in a MedPage Today article on the study. One is the most obvious — that a higher HbA1c level could result in more damage from a stroke, with greater cognitive impairment. Another is that higher HbA1c could cause worse cognitive performance independently of the stroke. And a third is that the effect could run in the other direction — that people with worse cognitive function might have worse blood glucose control because they can’t manage their diabetes as well. All, or just some, of these explanations could be correct.
To more fully understand whether better blood glucose control can, in fact, lead to less cognitive decline in people with diabetes who have a stroke, the researchers write that intervention studies are needed — studies in which researchers assign certain participants to receive a treatment that results in better blood glucose control, then compare their cognitive function after a stroke with a different group that didn’t receive the treatment to improve blood glucose control. But because only a small fraction of people with diabetes have a stroke during any period of time, this type of study would need to enroll many more participants — and last much longer — than simpler observational studies like the one described here.