We know that exercising and maintaining a healthy weight can help ward off dementia. We also know that people with Type 2 diabetes appear to be at least twice as likely to develop Alzheimer's disease than others. And now a provocative thesis suggests that Alzheimer's itself should be thought of as "Type 3" diabetes, or "diabetes of the brain." It's a theory that offers cause for both encouragement and concern.
A recent article by Brown Medical School neuropathologist Suzanne de la Monte in the Journal of Alzheimer's Disease detailed the connection between insulin and Alzheimer's. "Many of the unexplained features of Alzheimer's, such as cell death and tangles in the brain, appear to be linked to abnormalities in insulin signaling," she explained in a statement. "This demonstrates that the disease is most likely a neuroendocrine disorder, or another type of diabetes."
To reach her conclusions, de la Monte examined the brains of 45 deceased elderly Alzheimer's patients and found that among those "in the most advanced stage of Alzheimer's, insulin receptors were nearly 80 percent lower than in a normal brain." In healthy brains, insulin stimulates the enzyme that produces the neurotransmitter acetylcholine, the lack of which is seen as a key marker of Alzheimer's disease. In patients with Alzheimer's, de la Monte believes, the brain gradually becomes resistant to insulin.
Previous animal brain studies by de la Monte and others have supported the hypothesis that insulin resistance may be a root cause of Alzheimer's, although many researchers believe that it will emerge as just one of several possible causes, including genetics. Most Alzheimer's patients are not diabetics and while many appear to have insulin-signaling concerns, not all do.
An Epidemic Gaining Momentum
Like Alzheimer's, diabetes has no cure. According to the American Diabetes Association, there are already nearly 26 million diabetics in the country, a number that is growing. Many diabetics do not develop Alzheimer's, but there is measurable overlap and the rates of both diseases are rising. If fatty foods provoke insulin resistance in our brains, then, as New Scientist magazine put it in a recent cover story about the link between diabetes and Alzheimer's, "we may be unwittingly poisoning our brains every time we chow down on burgers and fries."
In the New Scientist article, SUNY-Albany neuroscientist Ewan McNay said: "The epidemic of Type 2 diabetes, if it continues on its current trajectory, is likely to be followed by an epidemic of dementia. That's going to be a huge challenge to the medical and care systems."
Some Hope for New Treatment
Traditional understanding of Alzheimer's has focused on beta amyloid plaques in the brain, but exactly how those plaques amass has challenged scientists. "I believe it starts with insulin resistance," de la Monte has said. "Once it gets going you are going to need to attack on multiple fronts."
The news that Alzheimer's could be a type of diabetes may not appear to be encouraging, but de la Monte offers a bit of hope. "If you could target the disease early," she has said, "you could prevent the further loss of neurons. But you would have to target not just the loss of insulin but the resistance of its receptors in the brain."
Envisioning Alzheimer's as a form of diabetes may lead to new treatments targeting insulin resistance that could finally help reverse some effects of the disease. In limited testing, delivering insulin via a nasal spray that helps it travel to the brain more efficiently has shown some promise in improving attention and performance on memory tests. That experiment, directed by Suzanne Craft of the University of Washington in Seattle, is being expanded with money from the federal National Institutes of Health to see how the spray affects 240 subjects already displaying some signs of dementia.
"The human brain evolved to seek out foods high in fat and sugar. But a preference that started out as a survival mechanism has, in our age of plenty, become a self-destructive compulsion," an editorial in New Scientist began. It concluded that "we may be left with only the option of medically blocking either the craving for fast food, or its consequences. That has its own complications, and sidesteps the problem rather than addressing it. But the human brain also evolved to find ingenious solutions to intractable problems. It may yet come to its own rescue."
In the meantime, remember that regular exercise can decrease one's risk of developing Alzheimer's by 40 percent. So while the scientists work to formulate those ingenious solutions, it's best for the rest of us to keep running.