Two recent studies suggest that memory loss and cognitive decline may be linked to (a) diabetes, (b) poor control of blood sugar levels by persons with diabetes, and/or (c) damage to retinal blood vessels, called retinopathy.
What is Retinopathy?
Retinopathy is a general term that describes damage to the retina, which is the thin, light-sensitive tissue that lines the inside surface of the eye. Nerve cells in the retina convert incoming light into electrical impulses, which are carried by the optic nerve to the brain. Retinopathy occurs when there is damage to the small blood vessels that nourish tissue and nerve cells in the retina.
Retinopathy is a frequent complication of diabetes and uncontrolled high blood pressure, and is a leading cause of blindness and low vision among adults in the United States. Diabetes and high blood pressure have also been linked to declines in memory and thinking abilities.
The First Study: The Women’s Health Initiative
Cognitive function and retinal and ischemic brain changes: the Women’s Health Initiative, published in the March 27, 2012 issue of Neurology, examined the association between retinopathy and cognitive decline in older women. Ischemic refers to a decrease in the blood supply to a bodily organ or tissue, caused by blood vessel constriction or obstruction.
The study suggests that damage to retinal blood vessels could indicate the presence of similar damage to blood vessels in the brain, causing problems with cognition, memory, and thinking. It included 511 women aged 65 and older who were simultaneously enrolled in the Women’s Health Initiative Memory Study and the Sight Exam Study. The Women’s Health Initiative was a major 15-year research program, concluding in 2006, that investigated the most common causes of death, disability, and poor quality of life in postmenopausal women: cardiovascular disease, cancer, and osteoporosis.
The women received annual tests of mental function for up to ten years to evaluate memory and thinking skills. They also had a single eye examination four years after entering the study and brain scans eight years after enrolling. According to WebMD,
Compared to women who did not show evidence of vessel damage to the eyes, these women had lower average scores on the memory and thinking tests. Brain scanning revealed that they also had more evidence of blood vessel damage within the brain. The findings suggest that even very early retinopathy may be an indicator for small vessel disease and a risk factor for blood vessel-related memory and thinking declines, says study author Mary Haan, DrPH, MPH, of the University of California, San Francisco. Larger studies with longer follow-up times will be needed to confirm the findings.
The Second Study: Diabetes, Glucose Control, and Cognitive Decline
Diabetes, Glucose Control, and 9-Year Cognitive Decline Among Older Adults Without Dementia, published in the June 18, 2012 issue of Archives of Neurology, is a ten-year study that examined whether having diabetes increased the risk of cognitive decline among elderly persons and if poor glucose control was related to impaired cognitive performance.
The 3,069 study participants were also enrolled in the Health, Aging, and Body Composition (Health ABC) study. The ongoing Health ABC study began in 1996 with 3,000+ community-dwelling white and black older adults, then aged 70 to 79 years, living in Memphis, TN or Pittsburgh, PA. The long-term goal of the study is to observe changes over time in body composition – particularly increased body fat and decreased muscle mass – that contribute to disability in older persons.
The study participants completed several tests of mental function at the beginning of the study and at selected intervals over the ten-year study period. Diabetes status was determined at the beginning of the study and during follow-up visits. The researchers concluded that
…among well-functioning older adults, diabetes and poor glucose control … are associated with worse cognitive function and greater decline. This suggests that severity of diabetes may contribute to accelerated cognitive aging.
This study supports the hypothesis that older adults with diabetes have reduced cognitive function and that poor glycemic [i.e., the effect of carbohydrates on blood sugar levels] control may contribute to this association. Future studies should determine if early diagnosis and treatment of diabetes lessen the risk of developing cognitive impairment and if maintaining optimal glucose control helps [lessen] the effect of diabetes on cognition.
Anahad O’Connor provides an excellent summary of the study results in Diabetes Linked to Memory Problems in Older Adults on the New York Times Well Blog:
The new research showed that over the course of about a decade, elderly men and women with diabetes — primarily Type 2, the form of the disease related to obesity and inactivity — had greater drops in cognitive test scores than other people of a similar age.
The more poorly managed their disease, the greater the deterioration in mental function. And the declines were seen not just in those with advanced diabetes. The researchers found that people who did not have diabetes at the start of the study but developed it later on also deteriorated to a greater extent than those without the disease.
VisionAware will provide updates of this research as they become available.
Sources: Neurology; WebMD; University of Florida; The New York Times Well Blog; Archives of Neurology