Maintaining control of blood glucose certainly can be challenging, but the importance of a healthy HbA1C levels extends not only to the body, but to the mind as well. This is because when people with diabetes get older, they are at increased risk of developing vascular dementia.
Vascular dementia is a dangerous form of dementia, where mini strokes and blood vessel blockage suddenly damage and destroy areas of the brain.1 While doctors understand how vascular dementia occurs, less is known about how cognitive decline, the precursor to dementia, develops…until now.
Long term effects of diabetes include multiple complications at the micro and macrovascular level, and it is very likely that this process starts early in the condition or even in the pre-diabetes status—and its effects are seen only after decades of living with diabetes.
Therefore, Initiating therapy for diabetes early and achieving optimal glucose control shortly after the diagnosis of diabetes is paramount. Early therapy not only delays or even prevents complications, it also allows tighter control in a younger, healthier population, thus, hopefully, decreasing the incidence of cognitive decline later in life.
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The results of over 20 years of research now reveals some insights into how diabetes is associated with cognitive decline. "Our results suggest that better control of diabetes [glucose control] in midlife may help stave off cognitive decline in later life," said Elizabeth Selvin, PhD, MPH, an associate professor at Johns Hopkins Bloomberg School of Public Health, who coauthored the study, which was published in the Annals of Internal Medicine.2
Dr. Selvin and her colleague's research dates back to 1987—culminating in 5 separate assessments of over 13,300 individuals who lived in Maryland, North Carolina, Minnesota, and Mississippi. The investigators used simple tests to assess basic memory, language, executive function, and processing speed, and then measured the subjects' HbA1C levels.
Finding the link between diabetes and cognitive decline is as tricky as it is arduous. Past efforts oftentimes didn't look into all the other factors that may associate with cognitive decline, for instance.
Besides diabetes—smoking, alcohol consumption, education level, body mass index, high blood pressure, genes, cholesterol, a history of heart disease or stroke—these can be associated with cognitive decline, which is why the measurements had to be carefully adjusted to isolate the effects of diabetes on cognitive function.
Dr. Selvin and colleagues found that people with diabetes had a 19% greater decline in their cognitive function, compared to those without diabetes. To put this into perspective, a 60-year-old person without diabetes would have the same level of speed and executive function as a 55-year-old adult with diabetes. Also, the longer a person had diabetes, the more likely their cognitive decline would be significant.
The study didn't just look at people with diabetes or without diabetes, though. Many of the patients had prediabetes, a condition typically characterized by having an HbA1C level between 5.7% and 6.4%. People with this condition also showed marked signs of increased cognitive decline.
These findings reopen the debate as to whether controlling glucose levels leads to a healthier mind in later life. While previous research has found that tightly controlling blood glucose showed no positive effects on cognitive decline,3,4 Dr. Selvin and colleagues argue those studies used older patients with rather short periods of treatment (3.3 years).
"Diabetes and glucose control are potentially modifiable and may offer an important opportunity for the prevention of cognitive decline, thus delaying progression to dementia," Dr. Selvin concluded.
"The full underlying etiology is still unclear, but this study adds to the growing evidence for a vascular basis for cognitive decline and dementia," Dr. Selvin said. "In particular, we know that diabetes can cause damage to the small vessels in the body."
"High glucose levels cause damage to the small vessels making the vessel walls weaker and less flexible. In the eye and kidney, holes can form and the capillaries can leak. We know less about what is going on in the brain, but it is possible that the elevated glucose levels are causing damage to the small vessels in the brain."
Although the data so far published is compelling, more studies are needed to corroborate these findings.
This study utilized the community-based, prospective cohort ARIC (Atherosclerosis Risk in Communities) study, which was supported through contracts from the National Heart, Lung, and Blood Institute (NHLBI). NHLBI also provided specific grants to support the gathering of certain data, as well as training grants to coauthors Andreea M. Rawlings, MS, and Andrea L.C. Schneider, PhD. Dr. Selvin was supported through a grant from the National Institute of Diabetes and Digestive and Kidney Diseases, and coauthor Rebecca F. Gottesman, MD, PhD, was supported by a grant from the National Institute on Aging.