Diabetes and Your Brain

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Former US Surgeon General Richard H. Carmona, MD, calls Alzheimer disease “diabetes of the brain.” I don’t know what he’s talking about. Is there a connection between diabetes and Alzheimer? If so, how can we protect ourselves?

Alzheimer disease affects 1 in 10 Americans over 65 years of age. According to the Salk Institute for Health Research, “Studies have shown that people with diabetes have a 30 to 65 percent higher risk of developing Alzheimer’s disease compared to non-diabetic individuals.” The increased risk applies to both Type 1 and Type 2 diabetes. Other studies, like this one from Japan, found that insulin resistance was linked with an elevated risk of developing plaques in the brain that are associated with Alzheimer disease.

The insulin resistance link seems crucial. In 2007, Northwestern University scientists reported that Alzheimer makes brain cells insulin resistant. As Web Editor Diane Fennell reported here, people started calling Alzheimer “Type 3 diabetes.”

This name may be misleading, though. The insulin resistance in the brains of people with Alzheimer may have little to do with diabetes. It seems to be caused by proteins called beta amyloids, found in large quantities in Alzheimer brain lesions. These proteins seem to strip insulin receptors from brain cells, so insulin (and glucose) can’t get through. This is called an “insulin-signaling defect.”

Higher-than-normal blood glucose may aggravate the effect of beta amyloids, though. In a study published online, investigators led by David R. Schubert, PhD, reported that blood vessels in the brain of young mice with diabetes are damaged by “the interaction of elevated blood glucose levels and beta amyloids.” The damage took place long before the first Alzheimer plaques appeared, but the mice suffered from significant memory loss and an increase in inflammation in the brain.

So it may be that low levels of amyloids, which wouldn’t cause problems if glucose levels were normal, start to cause damage when blood sugar levels are up. Or is something else going on? After all, in studies like the Japanese one mentioned above, insulin resistance contributes to beta amyloid deposits, even if blood glucose levels are close to normal.

Another Link
Consumption of saturated fat may be another connection between Alzheimer and diabetes.

Diabetes, insulin resistance, and Alzheimer disease are inflammatory conditions, and saturated fats can increase inflammation. This study from the University of North Carolina at Chapel Hill School of Medicine, published online April 10, 2011 in the journal Nature Immunology, finds that saturated fatty acids can activate immune cells to produce an inflammatory protein called interleukin-1beta. This inflammation causes insulin resistance. Interleukin is different from beta amyloid, but fat intake has also been found to help beta amyloids get into the brain. So possibly saturated fat intake can increase both of these inflammatory chemicals.

Is Insulin the Treatment?
There may be a bright side to the Alzheimer/diabetes connection. Researchers from the University at Buffalo have found that low-dose insulin suppresses production of a precursor to beta amyloids in obese people with Type 2 diabetes. The research, published in March online in the Journal of Clinical Endocrinology and Metabolism, suggests that “insulin could have a powerful, new role to play in fighting Alzheimer’s disease.”

A study from Italy describes at least 12 ways that insulin resistance can contribute to Alzheimer disease. The paper, “Possible implications of Insulin Resistance and Glucose metabolism in Alzheimer’s disease pathogenesis,” was published in the Journal of Cellular and Molecular Medicine, March 2011. After describing connections between inflammation, oxidation, various proteins, and insulin, the Italians conclude that, “Insulin appears to act as “neuromodulator”…improving learning and memory.”

Now, this is starting to sound like diabetes. Maybe more like Type 2 than Type 1, but all types maybe. Insulin isn’t a cure, but it keeps the cells functioning. It sounds as if keeping blood sugar levels down may prevent or slow down Alzheimer disease, and insulin may be a valuable part of the process, and may benefit the brain in other ways as well — another reason to consider insulin therapy early in Type 2. A pilot study in 2009, using inhaled insulin in people with mild Alzheimer but no diabetes, showed improvement in memory and daily functioning in the insulin group compared to placebo (inactive treatment).

It’s important to note that late-onset Alzheimer disease (the usual kind) tends to be slow-moving. Most people who have Alzheimer lesions in their brains don’t find out until they’re autopsied. They never had symptoms, or people didn’t notice while they were alive. So quite possibly, self-managing to reduce blood glucose levels and inflammation may mean that Alzheimer disease never plays a part in your life. Insulin may help.

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