Two new studies highlight the connections between diabetes and dementia. One adds to a growing body of evidence that diabetes, one of the most common medical disorders among older Americans, is a risk factor for Alzheimer's disease and other forms of dementia. But intensive treatments for diabetes in those who already have it have limited benefits in preventing memory loss and other symptoms, the other study found.
One study comes from Japan, where researchers studied more than 1,000 men and women aged 60 and older for an average of 11 years. People with type 2 diabetes, which affects the body's ability to control blood sugar levels, were at twice the risk of developing Alzheimer's and other types of dementia than those who did not have problems with blood sugar control.
“Our findings emphasize the need to consider diabetes as a potential risk factor for dementia,” said study author Dr. Yutaka Kiyohara of Kyushu University in Japan. “Diabetes is a common disorder, and the number of people with it has been growing in recent years all over the world. Controlling diabetes is now more important than ever.” The findings appeared in the medical journal Neurology, from the American Academy of Neurology.
The dementia risk remained high regardless of other medical conditions like high blood pressure, high cholesterol and smoking, which are also known to increase Alzheimer's. The risk of dementia was also higher in people who had so-called pre-diabetes, a condition marked by poor control of blood sugar levels. People with pre-diabetes often go on to develop full-blown diabetes.
The prevalence of diabetes continues to rise around the globe, and some past studies have found that the disease contributes to an increased risk for dementia. The disease is also linked to an increased risk of a myriad of health problems, including heart disease, strokes, loss of vision and kidney failure.
Diabetes may contribute to poor memory and diminished mental function in various ways. The disease damages tiny blood vessels throughout the body, including the eyes and extremities. Ongoing damage to blood vessels in the brain may be one reason why people with diabetes are, as a group, at higher risk of memory and thinking problems as they grow older.
Diabetes is also marked by impairment in the body’s ability to regulate blood sugar, or glucose, which may damage brain cells. Wide swings in blood sugar levels after meals, a characteristic of people with diabetes, has been linked to poorer mental acuity in seniors. The Japanese study found the risk of developing dementia significantly increased when blood sugar was still high two hours after a meal.
In the second study, called the ACCORD-MIND study, researchers at the National Institute on Aging, part of the National Institutes of Health, compared two types of treatment for diabetes. One involved intensive monitoring of blood sugar levels, which some studies have suggested may help to ameliorate symptoms. The other involved standard diabetes care, which involves less frequent blood sugar testing and is far less labor intensive.
The researchers measured levels of a blood substance called hemoglobin A1c, which is linked to blood sugar levels, in about 3,000 older men and women who had the disease for many years. They sought to determine whether rigorous treatments that sought to achieve intense control of blood sugar levels would have an effect on thinking and memory skills. All participants also underwent cognitive testing, and about one in five also received MRI brain scans to measure brain volume. Decreased brain volume has been linked to an increased risk of Alzheimer's and dementia. Memory and thinking tests revealed no difference between those who got intensive treatment compared to those who got standard diabetes treatment. People in the intensive treatment group had larger total brain volumes, though the practical impact on cognitive risk seemed small.
“While these findings do not support the use of intensive therapy to reduce the possible effects of diabetes on the brains of older people, it remains important for older adults with type 2 diabetes to continue well-established regimens to keep their blood glucose levels under control,” said Lenore J. Launer, Ph.D., who led the study. “Cognitive health is of particular concern in type 2 diabetes. We will continue to investigate how managing blood sugar levels might be employed to protect people with diabetes from increased risk of cognitive decline as they age.” While having diabetes can increase your risk of developing dementia, having the disease does not mean that you will develop Alzheimer's. Similarly, many people who develop Alzheimer's do not have diabetes.
But the findings of these and other studies underline the importance of prevention in helping to reduce Alzheimer's risk. Maintaining lifestyle measures, like keeping weight down and following a regular exercise regimen, can be important in avoiding diabetes -- and may help in maintaining brain health.
T. Ohara, Y. Doi, T. Ninomiya, et al: "Glucose tolerance status and risk of dementia in the community: the Hisayama study." Neurology, Vol. 77, Sept. 20, 2011, pages 1126-1134.
Lenore J. Launer, et al., “Effects of intensive glucose lowering on brain structure and function in people with type 2 diabetes (MIND): a randomised open-label substudy of the ACCORD trial,” Lancet Neurology. Published online September 27, 2011.