People with type 2 diabetes or in the early stages of getting the disease appear to be at an increased risk of developing the brain plaques of Alzheimer’s disease. The findings are troubling, as diabetes is becoming alarmingly common in the United States and many other countries and may contribute to the growing number of Alzheimer’s cases in coming years.
One in five older Americans has diabetes. Many more people, both young and old, have risk factors for the disease, including obesity and poor control of blood sugar. “Type 2 diabetes and Alzheimer’s disease are two epidemics growing at alarming levels around the world,” said study author Dr. Kensuke Sasaki of Kyushu University in Japan. “With the rising obesity rates and the fact that obesity is related to the rise in type 2 diabetes, these results are very concerning.”
Numerous studies have shown that obesity, including having lots of belly fat in middle age, is associated with an increased risk of Alzheimer’s disease and other forms of dementia. Diabetes and insulin resistance, or the inability of the hormone insulin to properly control blood sugar levels, are also linked to increased dementia risk. Diabetes and poor blood sugar control is also linked to an increased risk for mild cognitive impairment, a condition marked by difficulties in thinking and learning that may be an early transitional form of Alzheimer’s disease.
This study further confirms the link between diabetes and brain health by showing that people with diabetes or prediabetes, or poor control of blood sugar, are more likely to develop the telltale beta-amyloid brain plaques that invade the brains of those with Alzheimer’s. The findings were published in the journal Neurology, from the American Academy of Neurology.
In the study, researchers performed diabetes and memory tests on 135 seniors, average age 67, over the course of 10 to 15 years. During that time, about 16 percent developed Alzheimer’s disease.
After the participants died, researchers examined their autopsied brains for the physical signs of Alzheimer’s disease – the plaques and tangles that invade the brain. While 16 percent had symptoms of Alzheimer’s disease while alive, a total of 65 percent had plaques.
The study found that people who had abnormal results on three tests of blood sugar control had an increased risk of developing plaques. Plaques were found in 72 percent of people with insulin resistance, when the hormone insulin becomes less effective at lowering blood sugar. In contrast, plaques were present in only 62 percent of people with no indication of insulin resistance. The researchers did not find a link between diabetes and tangles in the brain.
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 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 findings underline the importance of maintaining lifestyle measures, like keeping weight down and following a regular exercise regimen, in avoiding diabetes and maintaining brain health. It is important to note, however, that having diabetes does not mean that you will develop Alzheimer's as you age. Rather, diabetes may put you at increased risk for developing these conditions. Similarly, many people who develop Alzheimer's do not have diabetes.
“Further studies are needed to determine if insulin resistance is a cause of the development of these plaques,” said Dr. Sasaki. “It’s possible that by controlling or preventing diabetes, we might also be helping to prevent Alzheimer’s disease.”
Jose A. Luchsinger, M.D., M.P.H.: “Insulin Resistance, Type 2 Diabetes, and AD: Cerebrocascular Disease or Neurodegeneration” (editorial). Neurology, Vol 75, pages 758-759, e-pub August 25, 2010.
T. Matsuzaki, M.D.; K. Sasaki M.D., Ph.D.; Y. tanizaki, M.D., Ph.D.; et al: “Insulin Resistance Is Associated With the Pathology of Alzheimer Disease: The Hisayama Study.” Neurology, Vol. 75, pages 764-770, August 25, 2010.