The Link between Type 2 diabetes and Alzheimer's disease

Recent statistics indicate that people with type 2 diabetes mellitus have nearly twice the risk of developing Alzheimer's disease as people without diabetes. While the exact reason for this is still being investigated, several interesting findings connecting the two diseases have emerged.

Type 1 vs. Type 2 Diabetes.   The American Diabetes Association reports that in 2012, 29.1 million Americans, or 9.3% of the population had diabetes.  Of these, 90 to 95% have Type 2 diabetes.  While both Type 1 and Type 2 diabetes are characterized by high blood sugar, the mechanism for the development of each type is very different.  Type 1 diabetes is considered to be an autoimmune disease in which the cells within the pancreas that produce insulin are destroyed, resulting in a deficiency of insulin. Without insulin to move sugar from the bloodstream into the body's cells, blood sugar rises. Type 2 diabetes, on the other hand, is considered a disease of "lifestyle".  Poor diet, inactivity, and obesity are major reasons for its development.  In type 2 diabetes elevated blood sugar levels are initially due to the body's inability to use insulin effectively. This is known as "insulin resistance" and is associated with higher than normal insulin levels.
 
Complications of Type 2 diabetes.   In addition to significantly increasing one's risk of heart attack and stroke, Type 2 diabetes mellitus is associated with a number of other medical complications including:

• Blindness from diabetic retinopathy
• Reduced blood flow in the feet and legs requiring amputations
• Kidney failure
• Nerve damage and ulcerations of the feet

If these problems weren't enough, add in the recent findings that Type 2 diabetes may also contribute to the development of Alzheimer's disease.

How could diabetes cause Alzheimer's?   When examining the brain of someone with Alzheimer's disease who has died, two major findings are noted: amyloid plaques and tau protein "tangles".  These are considered to underlie the neurodegenerative process related to development of dementia.  Recent research has shown that the high insulin levels (hyperinsulinemia) from Type 2 diabetes cause changes in the tau protein that result in the tangles.  Another study performed with mice demonstrated that high levels of glucose in the blood can increase amyloid beta, a key component of amyloid plaques, clusters of "sticky" proteins that inhibit the normal function of brain cells. While the relative contribution of high blood sugar or high insulin levels is still under investigation, one or both of these features of
Type 2 diabetes is likely responsible for the increased development of Alzheimer's.

Reducing Alzheimer's risk.  By avoiding the development of Type 2 diabetes, the risk of developing Alzheimer's goes down in parallel. This is best done by staying physically active, eating a healthy diet and keeping one's weight in an ideal range.  In someone who already has Type 2 diabetes, most of the known complications can be prevented or delayed with regular visits to a health care provider, appropriate medication and attention to lifestyle issues.  It stands to reason that these measures would reduce the risk of developing Alzheimer's disease also.  One study performed by scientists at Kaiser Permanente demonstrated a 20% reduction in the development of dementia when treating Type 2 diabetics with the diabetes medication, metformin. While many cases of Alzheimer's disease seem to develop by chance, prevention or management of Type 2 diabetes appears to offer an opportunity to reduce the likelihood of its occurrence.