Is Alzheimer's Disease really "Type 3" Diabetes?

A rising health concern throughout the world is diabetes. The number of people diagnosed with diabetes in 1985, around 30 million, increased nearly ten fold to 285 million in 2010. Similarly there has been an increase in the amount of cases of Alzheimer’s disease. Although the increase in these two dispositions may appear coincidental research has shown that there is a correlation between diabetes and Alzheimer’s disease. More specifically research has focused on the role insulin plays in the body and recently the brain.
First, it is important to understand what the role of insulin in the body is. Insulin’s primary job in the body is to allow for cells to intake glucose, or sugar, in order to use as energy. Diabetes is a disease in which for some reason insulin fails to complete its job. There are two main types of diabetes: Type 1 and Type 2, also apart of Type 2 is Gestational diabetes mellitus (GDM) which is the onset of diabetes during pregnancy. According to some researchers there is a “Type 3 diabetes.” Although not universally recognized due to lack of research, Alzheimer’s disease is sometimes referred to as “Type 3 diabetes.” Now you’ll probably ask, how can insulin relate to a neurodegenerative disease like Alzheimer’s? The answer is that insulin’s role in the brain is as important and more complex than throughout the rest of the body.
In the brain insulin is most concentrated and active within the hippocampus and frontal lobes. The hippocampus functions as the memory center of the brain and insulin affects the hippocampus by regulating the neurotransmitter acetylcholine. Acetylcholine basically acts as a bridge between stimulus, insulin, and brain function, memory and learning. The question then arises, what turns a normally functioning insulin receptor inactive? Insulin resistance is the cause of decreased insulin sensitivity and diabetes.

Insulin resistance involves normally healthy neurons becoming unable to respond to insulin stimuli. The picture shows how some insulin receptors are active while others are non-responsive. Because the neurons are not processing the signals from insulin, the cell in not able to take in glucose. This means that the cell does not receive the energy required to facilitate normal cellular functions and excess glucose stays in the blood stream. Without a source of energy brain cells within the hippocampus and frontal lobes enter their termination state and begin to die. Based upon this, researchers focused in Alzheimer’s disease believe insulin resistance is a cause for the neurodegeneration associated with Alzheimer’s disease.
Compared with the rising levels of diabetes throughout the world the number of cases of Alzheimer’s disease is likewise increasing. A likely cause of this correlative increase is due to the poor eating habits that are on the rise in the united states. The onset of diabetes continues to occur at earlier ages and thus the likelihood of earlier onset of Alzheimer’s disease is also expected, although more research is needed on this topic. The genetic consequences of permanent insulin resistance are more likely to cause a predisposition to Alzheimer’s disease in the children of those who possess insulin resistance. Further studies is required to fully understand the consequences of insulin resistance on the brain as well as the development of Alzheimer’s disease based on that resistance.
Sources:
http://www.hbo.com/alzheimers/science-insulin-in-the-brain.html
http://diabetes.niddk.nih.gov/dm/pubs/insulinresistance/
http://www.jci.org/articles/view/59903
http://onlinelibrary.wiley.com/doi/10.1111/j.1582-4934.2011.01318.x/full