While the death rates from many chronic diseases have stabilized or declined over the past 2 decades, there have been 2 exceptions. The rates of diabetes and Alzheimer’s have dramatically increased. Their parallel increase is not surprising as diabetes is a major risk factor for Alzheimer’s. Newer research is now suggesting that the relationship may begin sooner than the appearance of the diabetes.
Type two or “adult onset” diabetes has one of the most established relationships to dietary patterns. It is largely a disease of “carbohydrate intolerance” brought on by excessive simple sugars and refined carbohydrates in the diet. This pattern of eating over time leads to insulin resistance where cells become poorly responsive to insulin. In the early stages the body produces excessive insulin trying to force cells to respond to insulin. Blood sugar is maintained at normal levels by the excessive insulin so without measuring blood insulin levels the problem remains hidden.
The importance of the insulin resistance/normal blood sugar phase is that it has now been demonstrated that changes in brain function representing “pre-Alzheimer’s” occur in this phase.(1) Using functional MRI which shows the ability of brain areas to activate during memory tasks, this study showed that in those with insulin resistance that the core brain areas that process memory were impaired in their functioning. The ability to process recall memory was also examined with a memory test called “what, where, when” (WWW). Subjects are shown successive diagrams briefly and then their ability to recall what was seen, where it was in a diagram and when in the series it appeared. As the diagram shows, the WWW memory was diminished 50% in those with insulin resistance.
The concern with this observation is that the abnormal brain functioning seen in Alzheimer’s disease begins to be seen long before its onset when insulin resistance is present. New study has now shown that the process appears to begin even before insulin resistance occurs with the behavior that eventually causes insulin to dysfunction, simply eating higher amounts of sugar!
This new data emerged as a new part of the famous Framingham Heart Study.(2) This branch of the study followed over 4200 adults with standard testing used to evaluate the presence of either pre-Alzheimer’s called MCI or Alzheimer’s. Testing included neuropsychological testing and volumetric MRI which is a sensitive measure of actual brain loss that is the hallmark of Alzheimer’s. The adults were also assessed for daily sugary beverage intake. Sugary beverage intake has been found to be a stable marker reflecting general sugar intake levels. The findings were striking.
The volumetric MRI showed that those who consumed 1 or more sugary beverages daily had a significantly greater loss of total brain volume, and this was especially present in the hippocampus, a primary memory processing area. Neuropsychologic testing revealed a similar pattern on memory testing with significant losses associated with 1 sugary beverage/day and even greater loss with 2 or more. They concluded that the memory loss was equivalent to 3.5 – 13 years of brain aging.
The researchers conclusions tell it all, “Our results provide further evidence that sugary beverage consumption is associated with markers of preclinical Alzheimer’s in humans.” So while the earliest understanding of the relationship between the whole sugar dynamic was that elevated blood sugar in the form of diabetes increased Alzheimer’s risk, the current understanding suggests that relationship begins much earlier. The next understanding was that the damage to the brain which drives Alzheimer’s could be shown in the early phase of prediabetes, insulin resistance.
The most recent understanding is the damage begins even before insulin resistance begins simply associated with eating high amounts of sugar which correlates both with brain volume loss and impaired memory testing. This relationship had been demonstrated in animals for about decade. The caution cited in these studies has been that the result may not translate into a relationship between sugar consumption and Alzheimer’s in humans as it does in animals. The translation has now been done.
Some of the other important points the researchers discussed include:
To get ahead of the rapidly increasing rates of Alzheimer’s we need to start with the modifiable lifestyle factors that are associated with the disease. Consuming the amount of sugar that has become typical in the Western diet is a major one.
Cheke et al. Obesity and insulin resistance are associated with reduced activity in core memory regions of the brain. Neuropsychologia, 2017;96:137–149.
Pase et al. SUGARY BEVERAGE INTAKE AND PRECLINICAL ALZHEIMER’S DISEASE IN THE COMMUNITY. Alzheimer’s & Dementia, 2017 ePub, 1-10.