Having poorly controlled type 2 diabetes — rather than just diabetes itself — was linked to a much higher risk for cognitive impairment and dementia in a new study published in the journal Alzheimer’s & Dementia.
Researchers have long known that having diabetes is linked to a higher risk for dementia. But it hasn’t always been clear to what degree dementia may develop due to elevated blood glucose levels, or whether it develops at least in part due to cardiovascular risk factors that are common in people with diabetes. There has also been uncertainty about whether elevated blood glucose levels raise the risk for a precursor to dementia, known as cognitive impairment without dementia. For the latest study, researchers were interested in whether elevated blood glucose levels contributed to cognitive impairment in people without it, or to developing dementia in people with cognitive impairment.
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The study participants were 2,522 adults who took part in the Swedish National Study on Aging and Care–Kungsholmen, all of them residents of central Stockholm. The age of participants ranged from 60 to 102, with an average age of 72.3. None the participants had dementia, and 1,840 didn’t have cognitive impairment of any kind, while 682 had cognitive impairment without dementia. When it came to diabetes status, 217 participants had type 2 diabetes and 860 had prediabetes, while the rest had normal blood glucose levels (people with type 1 or a number of other health conditions were excluded from the study). Participants were followed for 12 years until 2016, during which a variety of health measurements were taken and cognitive status was monitored.
During the follow-up period, 484 people in the group without cognitive impairment died (26.3%), while 311 people in the group with cognitive impairment died (45.6%). Another 391 people in the group without cognitive impairment, and 142 in the group with cognitive impairment, dropped out of the study. By the end of the study, there had been 544 new cases of cognitive impairment among participants who began the study without the condition. And among participants who started out with cognitive impairment, there had been 151 new cases of dementia.
After adjusting for the age and sex of participants, the researchers found that the rate of new cases of cognitive impairment was 36.4 per 1,000 person-years for participants with normal blood glucose levels, 44.6 for those with prediabetes, and 54.3 for those with diabetes. The rate of new dementia cases among participants who started out with cognitive impairment was 36.7 for those with normal blood glucose levels, 40.5 for those with prediabetes, and 46.7 for those with diabetes.
When the researchers adjusted for a number of factors known to affect the risk for cognitive problems — including age, sex, education level, physical activity, body-mass index (a measure of body weight that takes height into account), heart disease, and high blood pressure — they found that compared with participants who had normal blood glucose levels, those with prediabetes were 12% more likely to develop cognitive impairment, and those with diabetes were 34% more likely. Among participants who started out with cognitive impairment, compared with participants with normal glucose, those with prediabetes were 19% less likely to develop dementia, while those with diabetes were 7% more likely.
Poorly controlled diabetes, not diabetes itself, linked to increased dementia risk
But there was a major difference between participants with well-controlled diabetes — defined as an A1C level (a measure of long-term blood glucose control) below 7.5% — and those whose diabetes wasn’t well controlled when it came to the risk for cognitive impairment or dementia. Compared with participants with normal glucose, those with well-controlled diabetes were 20% more likely to develop cognitive impairment, while those with diabetes that wasn’t well controlled were 101% more likely. And among participants who started out with cognitive impairment, compared with those who had normal glucose, those with well-controlled diabetes were 26% less likely to develop dementia, while those with diabetes that wasn’t well controlled were 187% more likely to develop dementia.
The researchers concluded that while having diabetes didn’t by itself increase the risk for dementia, having diabetes that wasn’t well controlled drastically increased the risk for dementia among people with cognitive impairment. These results point to the importance of good blood glucose control in older people with type 2 diabetes who are at greater risk for cognitive impairment or dementia.
Want to learn more about maintaining cognitive health with diabetes? Read “Nine Tips to Keep Your Memory With Diabetes,” “Staying Sharp: Seven Ways to Keep Your Brain Healthy With Diabetes,” “Keeping Your Brain Strong With Diabetes” and “Memory Fitness: How to Get It, How to Keep It.”