A new study of over 1,000 adults age 60 and above, conducted by researchers in Japan found that those with diabetes had about twice the risk of developing Alzheimer’s dementia and 1.74 times the risk of developing dementia of any kind within 15 years, compared to those without diabetes.
The study, by Yutaka Kiyohara, MD, PhD, of Kyushu University in Fukuoka, Japan, and colleagues, was published in the September 20, 2011 issue of Neurology®, the medical journal of the American Academy of Neurology.
“Our findings emphasize the need to consider diabetes as a potential risk factor for dementia,” said Dr. Kiyohara, the study’s principal author. “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.”
As to the growing prevalence of diabetes and ways to prevent it, see our previous reports on:
- Diabetes Pandemic Linked to Obesity Epidemic; Study Finds Early Diet Intervention Helps and
- CDC Reports Number of Americans with Diabetes Or Prediabetes Has Risen Dramatically; Losing Weight & Exercise Can Prevent or Delay the Disease.
Previous studies had found a link between diabetes and Alzheimers Disease, but not Vascular Dementia, and other studies had found contrary results. “These conflicting results may have been related to differences in the study designs, including the defined criteria for diabetes and dementia subtypes,” the authors of the current study hypothesized.
This new study was one of the first large studies to verify a significant link between diabetes and both Alzheimer’s Disease and all-cause dementia using rigorous study methodology to avoid definitional issues in identifying the incidence of the diseases.
For the study, a total of 1,017 people in Japan who were age 60 and older were given an oral glucose (sugar) tolerance test after an overnight fast to determine if they had diabetes at the beginning of the study period. None of the participants had dementia at the start of the study.
Study participants were monitored for an average of 11 years and then tested for dementia, with a total of 15 years follow-up. The cases of dementia were all diagnosed based on scientific tests using either brain scans or autopsies, or in some cases both.
During the study, 232 people (22% of the participants) developed dementia.
Through their analysis of the data, the researchers found that over the study period, people with diabetes were 2.05 times as likely (about twice as likely) to develop Alzheimer’s Disease as people with normal blood sugar levels, and 1.74 times as likely to develop dementia of any kind as those with normal blood sugar levels. After adjustments, the risk of developing Vascular Dementia was found to be 1.82 times as high in those with diabetes as in those with normal blood sugar levels.
Of the 150 people with diabetes, 41 developed dementia, while of the 559 people without diabetes, 115 developed dementia.
The results remained the same after the researchers controlled for factors such as high blood pressure, high cholesterol and smoking.
The risk of dementia was also found to be higher in people who did not have diabetes, but had impaired glucose tolerance, or were “pre-diabetes.”
In addition, the study found the risk of developing dementia significantly increased when blood sugar was still high two hours after a meal.
How Does Diabetes Lead to Dementia?
The study did not measure the mechanism by which diabetes may lead to Alzheimer’s or other dementia, and the researchers called for further study into this.
The authors, however, mentioned previous studies that suggested “possible pathophysiologic mechanisms through which diabetes or elevated blood glucose levels might affect the initiation and promotion of dementia.” Among the possible mechanisms mentioned:
- Insulin resistance (which causes high blood sugar and may lead to type 2 diabetes), may disrupt the body’s ability to break down an amyloid protein which forms plaques in the brain that have been linked to Alzheimer’s.
- High glucose (blood sugar) levels also produces molecules that contain oxygen, which in a process called “oxidative stress,” can damage cells.
- High blood sugar and high cholesterol may lead to atherosclerosis, a hardening and narrowing of arteries in the brain, which can lead to vascular dementia. Vascular dementia is known to occur when blocked arteries (including from strokes) kill brain tissue.
“Our findings suggest that diabetes is a significant risk factor for all-cause dementia, AD [Alzheimer's Disease], and probably VaD [Vascular Dementia],” the authors concluded.
They called for further study into the mechanisms by which diabetes may lead to dementia. “Further studies are needed to elucidate the pathogenesis of hyperglycemia and diabetes in the development of dementia,” they wrote.
The full study report is available in the September 20, 2011 issue of Neurology®, the medical journal of the American Academy of Neurology.
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