Scientists have yet to discover why Alzheimer's disease develops, but research conducted in recent years has shown that diabetes heightens an individual's risk. Past studies examining this link have shown that low levels of insulin, which characterizes diabetes, may also interfere with normal brain functions and lead to Alzheimer's. In a new study, researchers at the Salk Institute for Biological Studies investigated a related mechanism that may also explain this link: the connection between Alzheimer's, diabetes, and high blood glucose levels, which are caused by the body's inability to process insulin. Their work, which will appear in the journal Neurobiology of Aging, indicates that an interaction between blood glucose and beta amyloid may contribute to the progressive cognitive decline of Alzheimer's.
According to the study, diabetics have a 30 to 65 percent greater chance of developing Alzheimer's, a risk that applies to individuals with both type I and type II diabetes. In both forms of the disease, low insulin levels lead to high blood glucose levels, and the researchers theorized that this symptom may affect the brain's ability to function in some way. To test this idea, they assessed memory and learning in diabetic mice that were also prone to develop Alzheimer's but had not yet shown symptoms. Compared to mice that were either diabetic or genetically vulnerable to Alzheimer's, mice that were both diabetic and contained the predisposition displayed greater cognitive decline over time.
Although these mice were presymptomatic for Alzheimer's and did not have amyloid plaques or other signs of the disorder, evaluations of their brains revealed that biological mechanisms associated with both conditions affected the brain in a way that could impair cognitive abilities. The researchers found that interactions between high levels of blood glucose and low levels of beta amyloid led to an abnormal increase in the production of harmful molecules, including free radicals. These molecules damaged blood vessels and caused inflammation in the rodents' brains, both of which contributed to cell death and cognitive decline.
Rates of Alzheimer's and diabetes are increasing among Americans, and the nation's growing obesity problem as well as an aging population have contributed to this escalation in diagnoses. This research furthers our understanding of how diabetes raises an individual's risk for Alzheimer's, and it may provide new directions for researchers searching for a treatment that can slow the progress of the disorder or even prevent it. Additionally, this study demonstrates how physical and mental health intertwine. While there may be other factors at play in the development of Alzheimer's, we can lower our risk for this and other forms of dementia by maintaining an active lifestyle, eating well, and taking other steps to prevent diabetes and other health problems.
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