September 20, 2011

People with diabetes are at increased risk of having a heart attack or stroke at an early age, and diabetes appears to dramatically increase a person's risk of developing Alzheimer's disease or other types of dementia later in life, according to a new study conducted in Japan and led by Yutaka Kiyohara, M.D., an environmental medicine researcher at Kyushu University, in Fukuoka. The study included more than 1,000 men and women over age 60. At the beginning, tests showed that 15% of the participants had full-fledged diabetes, while 23% had prediabetes, also known as impaired glucose tolerance. The participants were all dementia-free when the tests were done, but over the next 15 years 23% received a diagnosis of dementia. Slightly less than half of those cases were deemed to be Alzheimer's disease, with the remainder roughly split between vascular dementia and dementia due to other causes. The diagnoses were confirmed with brain scans of living patients and brain autopsies in deceased patients. Both diabetes and prediabetes were associated with an increased risk of dementia diagnosis, although the association was weaker for prediabetes. And the link persisted even after the researchers took into account several factors associated with both diabetes and dementia risk, such as age, sex, blood pressure, and body mass index. The researchers found that people with diabetes were twice as likely as the other study participants to develop Alzheimer's disease within 15 years. They were also 1.75 times more likely to develop dementia of any kind. Diabetes could contribute to dementia in several ways, which researchers are still sorting out. Insulin resistance, which causes high blood sugar and in some cases leads to type 2 diabetes, may interfere with the body's ability to break down a protein (amyloid) that forms brain plaques that have been linked to Alzheimer's. High blood sugar (glucose) also produces certain oxygen-containing molecules that can damage cells, a process known as oxidative stress. In addition, high blood sugar -- along with high cholesterol -- plays a role in the hardening and narrowing of arteries in the brain. This condition, known as atherosclerosis, can bring about vascular dementia, which occurs when artery blockages (including strokes) kill brain tissue. Studies dating back to the late 1990s have suggested that people with diabetes are more likely to develop Alzheimer's disease and other types of dementia. The next step will be to understand whether controlling blood sugar and reducing risk factors for type 2 diabetes also reduces dementia risk. Before it’s too late, I’d just like to say, it’s been nice to know you.