In a new report published in the December issue of the journal Diabetes Care, it is predicted that in the United States the number of people suffering from Diabetes will double over the next 25 years. This is bad news for those of us concerned about the looming epidemic of Alzheimer's Dementia.
Diabetes is a disease of metabolic function in the body that is defined as an inability to control levels of sugar in the blood. However, Diabetes does far more than disturb blood sugar levels. Diabetes adversely affects the functions of virtually every organ in the body. Consequently, it is a major risk factor for heart disease, stroke, and other illness, among which are various forms of dementia.
There are actually two types of diabetes. Diabetes Type I, often referred to as Juvenile Onset Diabetes, is most often seen in children and young people. This form of Diabetes results from a loss of pancreatic function and subsequent decrease in the production of the essential hormone, insulin. The other, far more common form of Diabetes is Diabetes Type II, or what is sometimes referred to as Adult Onset Diabetes. Diabetes Type II is not primarily due to a lack of insulin, but rather to a loss of the body's sensitivity and response to insulin. Whereas Diabetes Type I is usually caused by infections or autoimmune diseases of the pancreas, Diabetes Type II is almost always the result of poor diet, stress and lack of exercise. That is, it is generally the result of poor lifestyle choices. It is Diabetes Type II that is expected to grow in such disturbing fashion over the next 25 years.
Diabetes Type II is a major risk factor for Alzheimer's Dementia. Indeed, having Diabetes Type II is thought to at least double the risk of developing Alzheimer's Dementia. Over the last ten years we have greatly increased our understanding of the relationship between Diabetes Type II and Alzheimer's. The most obvious reason that Diabetes increases the risk of Alzheimer's Dementia is because it increases the incidence of heart disease; high blood pressure; high levels of fat in the form of triglycerides in the blood; decreases in the levels of the good cholesterol, HDL; and increases in levels of the bad cholesterol, LDL. All of these factors are individually known to increase the risk of Alzheimer's Dementia. These conditions also increase the risk of stroke and other forms of damage to blood vessels in the brain, which thus increases the risk of vascular dementia. Unfortunately, vascular dementia accelerates the pathological changes that occur in Alzheimer's Dementia. Thus, vascular dementia is itself a risk factor for Alzheimer's Dementia.
It has more recently become apparent that insulin itself plays an important role in brain chemistry, and that disturbances in the body's response and sensitivity to insulin may play a role in the pathology of Alzheimer's Dementia. Thus, in respect to the growing epidemic of Alzheimer's Dementia, the predicted increase in the incidence of Diabetes is particularly ominous. The hallmarks of the damage done to brain tissue in Alzheimer's Dementia are plaques of abnormal amyloid protein, and tangles of abnormal forms of the brain protein tau. Insulin plays an important role in maintaining normal forms and functions of those proteins. A lack of insulin or insufficient sensitivity to insulin in the brain results in increased build up of amyloid plaques.
Interestingly, the enzyme that breaks down insulin in the brain after it has served its purpose, an enzyme known as Insulin Degrading Enzyme (IDE) is also able to destroy amyloid plaques. Insulin stimulates the production of IDE, and when there is insufficient insulin activity, there is also a decrease in the presence of IDE that could help reduce amyloid plaque build up. Another curious relationship between amyloid and insulin is that amyloid protein resembles insulin closely enough to bind to insulin receptors in the brain and block the effect of insulin. Thus amyloid plaques further decrease the brain's sensitivty to insulin. Insulin also prevents the production of abnormal neurofibrillary tangles of tau protein by inhibiting an enzyme in the brain known as glycogen synthase kinase-3 (GSK3). GSK3 adds phosphate to tau protein and "hyperphosphorylation" of tau protein causes it to tangle.
Beyond its direct effects on amyloid plaques and neurofibrillary tangles of tau, insulin serves as a growth factor in the brain that helps maintain nerve endings where neurons communicate with each other. Maintenance of these nerve endings is essential for what is referred to as "neural plasticity". Neural plasticity allows us to learn and adapt to changing conditions, and without it our brain function deteriorates. Insulin acts to reduce inflammation in the brain. It is known that inflammatory processes play a major role in the progression of Alzheimer's Dementia.
Although increases in the incidence of Diabetes Type II will almost certainly increase the number of individuals who will develop Alzheimer's Dementia, there is also a hidden danger. In most cases, Diabetes Type II arises in individuals who have first developed the condition known as Metabolic Syndrome. Metabolic Syndrome is the presence of high blood pressure, abdominal obesity, high triglycerides, and low HDL cholesterol. The other characteristic of Metabolic Syndrome is high blood sugar. However, the levels of blood sugar in Metabolic Syndrome are not high enough to reach those necessary to diagnose Diabetes. In fact, Metabolic Syndrome is often referred to as "pre-Diabetes".
The underlying cause of Metabolic Syndrome is thought to be insulin resistance, and it is largely due to poor lifestyle choices, that is, too much sugar, too much saturated fat along with it, too much stress, and too little exercise. The frightening fact is that along with the doubling of cases of Diabetes Type II, there will also be an enormous and less apparent growth in the number of individuals with Metabolic Syndrome but not actual Diabetes. Unfortunately, Metabolic Syndrome, even when it does not progress to full-blown Diabetes Type II, is also a major risk factor for developing Alzheimer's Dementia.
The answer to this looming health catastrophe, which will destroy both lives and financial plans, is the dissemination and implementation of common sense protocols of preventative medicine. We must reduce our intake of sugars and simple carbohydrates; reduce our intake of saturated fats, particularly when consumed along with simple carbohydrates; fight obesity and maintain ideal weight; promote exercise and stress reduction; and build a health care system that is dedicated to prevention of disease and monitoring for signs of risk factors for disease that can be improved or reversed. If these steps are not taken, our society faces a heartbreaking and extraordinarily expensive future of ill health, regardless of what type of health care plan congress is able to establish.
Dr. Mendelson is the author of the new book, Beyond Alzheimer's.