In people with heart disease,
High blood sugar may add to mental decline in people with cardiovascular disease.
Years of poorly controlled diabetes has devastating consequences for your heart, blood vessels, kidneys, and eyes. However, subtler blood sugar abnormalities may also harm your thinking and memory power. In a pivotal 2009 study in Diabetes Care, researchers studied people with uncontrolled type 2 diabetes and other risks for cardiovascular disease and found a link between high blood sugar and problems with thinking and memory.
But does elevated blood sugar also have a bearing on brain power in people with heart disease, even if they do not meet the threshold of a diabetes diagnosis? That’s the question Dr. Allison Goldfine, associate professor of medicine at Harvard-affiliated Joslin Diabetes Center, sought to answer in her recent research. She and her colleagues conducted a battery of mental function tests on a group of men with stable coronary artery disease and cardiovascular risk factors. All were able to function independently and had no signs of advanced dementia.
The study looked at their performance on the cognitive tests in relation to their blood sugar levels, based on the HbA1c test. Their HbA1c levels were as high as 7.5%, the upper limit of well-controlled blood sugar in a person with diabetes, but well above the normal level for someone without the disease.
Blood sugar and brain function
“We found an association between higher HbA1c levels and many different measures of cognitive function, even across these low ranges of blood sugar elevation,” says Dr. Goldfine, whose report appeared in the January 2015 American Journal of Medicine. When considered in light of the earlier, similar findings, this indicates that thinking and memory function are progressively worse as blood sugar levels go up in people with cardiovascular disease, she says. The trend continues from normal blood sugars to HbA1c levels of 8.0% and higher.
Many possible mechanisms may explain the link between blood sugar and brain function, says Dr. Goldfine. One prime suspect is vascular dementia. Over time, diabetes damages small arteries in the brain, leading to ministrokes and brain tissue death. The result is a gradual loss of mental function. In addition, high blood sugar levels and insulin resistance appear to disrupt the communication pathways within the brain. Diabetes-related inflammation appears to be another culprit, especially in the development of amyloid plaques in the brain that are characteristic of Alzheimer’s disease.
The danger of lows
Episodes of very low blood sugar (hypoglycemia) leading to seizures or loss of consciousness can also have a lasting impact on thinking and memory. This is a particular problem for older adults who use insulin or certain oral diabetes medicines called sulfonylureas, which can drive blood sugar levels down rapidly. Older people’s brains are less adept at forming and altering brain cell pathways. As a result, they may have a harder time bouncing back from the challenges that come with hypoglycemic events, says Dr. Goldfine. Because of this danger, current medical recommendations advise people over age 65 against rigidly managing their blood sugar levels to meet near-normal parameters, for fear that this type of tight control could do more harm than good.
HbA1c refers to glycated hemoglobin (A1c), which reflects the average concentration of glucose (sugar) in your bloodstream over the last two to three months. For people with diabetes, higher HbA1c levels are linked to a greater risk of diabetes-related complications. Doctors class HbA1c levels as follows:
Aging in the mix
In the past, the major concerns in treating people with diabetes were complications such as kidney failure, heart disease, and amputations. However, early death from these and other problems is being forestalled with more effective treatment strategies. As a result, new concerns such as brain impairment are coming forward.
A question still to be answered is whether these problems are more apparent because people with diabetes are living long enough to face so-called diseases of older age. Alternatively, says Dr. Goldfine, diabetes itself hastens the aging process, so problems such as mental decline may become more severe and occur at younger ages. Future research may help establish the underlying mechanisms and point to new treatments, she adds.