High blood sugar linked to cognitive decline in stroke survivors

Loss of general thinking ability happens much faster in stroke survivors who had high blood glucose in the years after their health crisis, even after accounting for other things that might affect their brainpower, according to a new study published in JAMA Network Open.

Led by researchers from Michigan Medicine, the University of Michigan’s academic medical centre, the study is based on data from the STROKE COG study, which pooled, harmonised and analysed data from four long-term studies of groups of people across four decades. It includes data from nearly 1000 people who had detailed measurements of brain function and blood tests taken for years before and after they had a stroke — including 781 who had two or more brain function tests in the years after their stroke. Nearly 800 of the entire group also had a gene test for the APOE4 genetic variation that is associated with high risk for Alzheimer’s disease.

“Having a stroke increases a person’s risk of dementia up to 50-fold, but we lack a comprehensive treatment approach that could reduce this risk, other than preventing a second stroke,” said Deborah A Levine, first author of the study and professor of medicine and neurology at U-M Medical School, whose previous work showed the role of stroke in accelerated cognitive decline.

“These findings suggest that higher cumulative blood sugar levels after stroke contribute to faster cognitive decline, and hyperglycaemia after stroke, regardless of diabetes status, could be a potential treatment target to protect post-stroke cognition.”

Those whose blood pressures or cholesterol were high after their stroke did not lose points on tests of thinking ability as quickly as those with high blood sugar, despite their role as risk factors for having a stroke. The researchers got the same results when they focused on people with a high genetic risk for dementia.

The researchers adjusted the data for differences in age, income, education, use of tobacco and alcohol, body mass index, heart disease and kidney function, and use of medications to treat high blood pressure, cholesterol and blood sugar. Post-stroke blood sugar measurements were taken an average of two years after their first stroke; about 20% of the study participants were taking diabetes medication before their stroke. None of the factors was linked to a faster loss of memory or executive function, which measures complex decision-making ability.

The study suggests the need for clinical research to test whether tight glycaemic control in stroke survivors reduces post-stroke cognitive decline and dementia in those with and without diagnosed diabetes. Tight glycaemic control has been shown in people with diabetes to reduce small blood vessel complications in the eyes, kidney and nerves; it may also decrease small blood vessel disease in the brain, but this is unproven.

In the meantime, people who have survived strokes and mini-strokes are advised to work with their healthcare teams to determine the best approach to testing and managing blood sugar for them — especially if they have pre-diabetes or diabetes. Levine noted that going too low on blood sugar levels in older adults also has risks, including dementia, and should be avoided.

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