April 17, 2007
Add memory loss to the long list of ills that may afflict people with diabetes, an ailment that strikes a growing proportion of our overweight and out-of-shape population. People with diabetes, a metabolic disease marked by wide swings in blood sugar levels, are at increased risk for heart disease, numbness and tingling in the hands and feet, vision loss, and other ills.
A new study finds that diabetes is also linked to an increased risk for mild cognitive impairment, a condition marked by difficulties in thinking and learning. In some people, mild cognitive impairment may be an "early," transitional form of Alzheimer's disease. About one in five people over age 65 has type 2 diabetes, a chronic ailment marked by poor control of blood sugar (glucose). Diabetes is especially common in older people who are overweight, though it is becoming increasingly common in younger persons as well, including children and teens who carry excess pounds. Many people with diabetes must take daily injections of insulin, a hormone released by the pancreas, to help control their blood sugar.
"Among cardiovascular risk factors [which are known to increase the risk of dementia], type 2 diabetes has been consistently related to a higher risk of Alzheimer's disease," say the authors of the current study, which appeared in the April issue of the Archives of Neurology, a journal published by the American Medical Association.
"Our results provide further support to the potentially important independent role of diabetes in the pathogenesis of Alzheimer's disease."
What the Study Showed
In the current study, doctors at Columbia University Medical Center in New York studied 918 seniors (average age 75.9) who at the start of the study did not have any memory problems. They were given in-depth mental and medical exams every 18 months for up to 10 years, including medical histories and physical exams. They were also given neurological evaluations and tests to measure learning, memory, reasoning, and language skills. Of the study participants, almost one in four had diabetes, more than 68 percent had high blood pressure, a third had heart disease, and 15 percent had had a stroke.
After an average of six years of follow-up, 334 individuals developed mild cognitive impairment. That total included 160 "amnestic" cases of MCI, a form of the disease marked by pronounced memory problems. Diabetes was related to a significantly higher risk of mild cognitive impairment overall, and of "amnestic" MCI in particular. That increased risk persisted, even after other risk factors were taken into account, including age, ethnic group, years of education, and heart and blood vessel disease.
"The [increased] risk of mild cognitive impairment attributable to diabetes was 8.8 percent for the whole sample, 8.4 percent for African-American persons, 11 percent for Hispanic persons, and 4.6 percent for non-Hispanic white persons, reflecting the differences in diabetes prevalence by ethnic group," the authors write.
Mild cognitive impairment, or MCI, is increasingly recognized as a transitional state between a healthy, mentally sharp brain and Alzheimer's disease. The amnestic form of mild cognitive impairment is particularly linked to Alzheimer's. The current study is one of many that have consistently linked type 2 diabetes with increased risk of Alzheimer's disease. Though here, risk is associated with MCI, which can be a precursor to Alzheimer's. It's important to note, however, that having diabetes does not mean that you will develop mild cognitive impairment or Alzheimer's as you age. Rather, diabetes may put you at increased risk for developing these conditions. Similarly, many people who develop mild cognitive impairment or Alzheimer's do not have diabetes. The authors call for continued study, in larger numbers of people, to better understand the link between diabetes and memory loss.
Prevention Is Key
The findings underline the importance of keeping weight down, following a regular exercise regimen, and maintaining other lifestyle measures designed to keep the body, and brain, healthy into old age. A "heart-healthy" lifestyle may not only protect the heart and ward off diabetes; it may help to keep Alzheimer's at bay as well, a growing body of evidence shows. If you already have diabetes, it is important to maintain tight control of blood sugar, using medications and regular medical check-ups.
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 feet. Ongoing damage to blood vessels in the brain may be one reason why people with diabetes are, as a group, at higher risk of cognitive loss as they grow older. Diabetes is also marked by impairment in the body's ability to regulate blood sugar (glucose), which in excessive amounts 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. Insulin, the hormone that regulates blood sugar levels, also plays a key role in diabetes.
Scientists at the Fisher Center for Alzheimer's Research at The Rockefeller University showed several years ago that insulin raises levels of beta amyloid secreted by cells that have been specially grown (cultured) in a laboratory. Beta-amyloid is a toxic protein that builds up in the brains of those with Alzheimer's.
For more on Alzheimer's and preserving your memory, visit www.ALZinfo.org.
Archives of Neurology, Volume 64, pages 570-575, April 2007.