In recent years a clear link has been established between Alzheimer’s disease and high blood sugar. Alzheimer’s is the most common form of dementia – around two thirds of New Zealanders suffering dementia have Alzheimer’s.

Two studies published within the last year confirm that the effects of a sugary diet and long-term high blood sugar are factors in Alzheimer’s disease, and the findings are threefold. Scientists found that people with consistently high blood sugar are more likely to get Alzheimer’s, and that Alzheimer’s sufferers exhibit high brain glucose and problems with the way the brain breaks down glucose.

One longitudinal study, published in April 2018 in Diabetologia journal, followed 5198 men and women from 2004 to 2015. Researchers found that people with long-term high blood sugar exhibited a faster rate of cognitive decline, regardless of whether they ever developed diabetes.

Another recent study, appearing in November 2017 in the Alzheimer’s & Dementia: the Journal of the Alzheimer’s Association, looked at autopsied brain tissue, gathered from the Baltimore Longitudinal Study of Aging (which has been running for almost 60 years). Higher levels of glucose were revealed in brains affected by Alzheimer’s. A link was also drawn “between abnormalities in how the brain breaks down glucose” and the symptoms and severity of Alzheimer’s disease.

 

The link with diabetes

The blood sugar revelation has led to Alzheimer’s being dubbed ‘Type 3 diabetes’ and ‘late stage diabetes’, though this is somewhat misleading.

Type 1 and type 2 diabetes themselves develop in completely different ways. Although both are characterised by high blood sugar and the inability of the body to regulate blood sugar properly, they have very different causes. Type 1 diabetes is an autoimmune disease, in which the immune system mistakenly attacks insulin-producing cells in the pancreas. It is usually diagnosed in childhood and must be treated with regular insulin injections. Type 2 diabetes is caused by poor diet and the body developing a resistance to insulin, and usually manifests in adulthood.

Type 2 diabetes is now a known risk factor for Alzheimer’s disease. But people with high blood sugar, but who are not categorised as diabetic, also have a higher risk of developing Alzheimer’s. So perhaps it’s more accurate to say that both diseases are a result of an unhealthy, sugary diet.

The other point to be aware of is that, although type 2 diabetes means you have a greater risk of Alzheimer’s, it’s also a risk factor for lots of other diseases, including heart disease and kidney disease, because the high levels of circulating glucose lead to fatty deposits that clog arteries and raise blood pressure.

 

Insulin resistance in the brain?

The real connection between diabetes and Alzheimer’s seems to an inability to effectively break down glucose. Recent research shows that insulin plays a more prominent role in the brain than previously thought. In fact insulin resistance in the brain seems to be a contributing factor for Alzheimer’s disease.

As far back as 2003, a review of research, drawing on studies from the previous 20 years, put forward the hypothesis that insulin resistance may be a factor in Alzheimer’s disease. The review pointed to evidence that “insulin-sensitive glucose transporters” are located in areas of the brain associated with memory and that “insulin may also play a role in regulating the amyloid precursor protein and its derivative beta-amyloid (Abeta), which is associated with senile plaques, a neuropathological hallmark of Alzheimer’s disease.”

Research into the link between Alzheimer’s disease and insulin resistance, as well as the role of insulin signaling in the brain, has intensified in the last few years. It’s now widely accepted that insulin signaling is indeed involved in various cognitive functions, including those that are impaired by Alzheimer’s.

Medical researchers are currently investigating whether administering insulin could have a therapeutic benefit in patients with the disease. For example, a study published in 2017 found that “long acting insulin detemir administered intranasally for three weeks enhanced memory for adults with Alzheimer’s disease”, but stressed the need for more extensive trials to verify these preliminary results and determine long-term benefits.

 

Insulin, resveratrol and metformin – potential treatments for AD?

We’ve discussed the potential for insulin to treat Alzheimer’s disease. What else is out there? While there is no known cure or proven treatment for Alzheimer’s, a lot of research is being dedicated to this very question. Two quite different medications have shown some promise in preliminary studies.

Resveratrol is a naturally occurring plant polyphenol with a number of benefits in terms of fighting age-related diseases. It has been shown by a significant body of research to improve cognitive function and slow brain aging. In a small-scale human study of 50-75-year-olds in 2014, which administered resveratrol daily for 26 weeks, participants exhibited improved memory, hippocampal functional connectivity and glucose metabolism.

Resveratrol has also been shown to help combat insulin resistance, which has implications for the treatment of both Alzheimer’s and type 2 diabetes.

Metformin is a prescription medication used to treat type 2 diabetes, controlling both blood sugar levels and insulin sensitivity. The good news is that it’s no longer controlled by drug companies – a generic form is available in many countries. However, the jury is out as to whether this diabetes drug could play a role in treating Alzheimer’s. Some studies show that it may reduce Alzheimer’s risk, and others suggest that long-term use may actually increase it. More research is needed to confirm its safety and efficacy in the prevention and treatment of Alzheimer’s.

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