New research done over the past few years has led scientists to use the term “type 3 – diabetes” when referring to Alzheimer’s disease. And while that definition on its surface doesn’t appear to make a whole lot of sense there is a lot more similarity to type 2 diabetes and Alzheimer’s than most people realize.
For example, they both share a problem with insulin. But what seems to be one of their more similar traits is the fact that they both appear to be another potential side effect of our sugary, Standard-American-Diet.
It’s also not uncommon for the path from sugar consumption to Alzheimer’s disease to move through type 2 diabetes, although a recent study shows that the progression doesn’t always work that way.
In a new longitudinal study, published in the medical journal Diabetologia, researchers followed 5,189 people over the course of 10 years. During that time, scientists discovered that people with high blood sugar levels suffered from a faster rate of cognitive decline than those with blood sugar in the normal ranges. These finding were independent of the fact as to whether the subjects blood sugar levels technically made them diabetic or not. In essence, the higher the average blood sugar readings, the faster the person suffered from cognitive decline.1
Lead author, Wuxiang Xie at Imperial College London said in an email statement, “Dementia is one of the most prevalent psychiatric conditions strongly associated with poor quality of later life. Currently, dementia is not curable, which makes it very important to study risk factors.”
Melissa Schilling, a professor at New York University, published a review of the literature in The Journal of Alzheimer’s Disease and connected the two diseases back in 2016.2
Her goal in reviewing the literature was to make sense of two somewhat confusing trends. The fact, that people with type 2 diabetes are twice as likely to develop Alzheimer’s disease and the fact that diabetics treated with insulin are also more likely to develop Alzheimer’s. Several studies have revealed the fact that elevated levels of insulin, increase the risk of developing Alzheimer’s.
However, the most confusing part is that type 1 diabetics who don’t make insulin are also thought to have an increased risk of developing Alzheimer’s. A finding that appears to contradict the other.
The theory Schilling has proposed is that it’s because of the insulin-degrading hormone, a by-product of insulin that breaks down both insulin and amyloid proteins in the brain. These amyloid proteins are the same proteins that clump together and lead to Alzheimer’s disease.
People who don’t make enough insulin, like those who have diabetes and are no longer producing enough insulin are also not producing enough of the enzyme to break down those brain clumps.
And for those who use insulin to treat diabetes and are left with excessive insulin the majority of the enzyme gets used up in an effort to break down that excess insulin, leaving a lack of the enzyme to address the amyloid proteins.
Schilling suggests, that this can happen in people who haven’t even been diagnosed with diabetes yet. A condition often referred to as prediabetes. What this means is that essentially your blood sugar is higher than normal, but not quite in the diabetic ranges yet.
And while Schilling isn’t primarily known as a medical researcher, Rosebud Roberts, a professor of epidemiology and neurology at the Mayo Clinic, agrees that she is interpreting the data correctly.
In a prior study published in 2012 in The Journal of Alzheimer’s Disease, Roberts looked at close to 1000 test subjects and separated them into four groups based on their carbohydrate intake.3
Those that had the highest carbohydrate intake were 80% more likely to develop mild cognitive impairment – a condition that is a primary step towards dementia, when compared to those who ate the lowest amount of carbs.
Mild cognitive impairment, or MCI allows people to dress and feed themselves but makes it difficult for them to perform more complex tasks. Research shows that preventing MCI can also prevent dementia.
And while these theories do appear to have merit, other researchers warn that we can’t jump to conclusions. Rebecca Gottesman, a professor of neurology at Johns Hopkins, says that the findings on carbs aren’t as well-established as those on diabetes. “It’s hard to be sure at this stage, what an ‘ideal’ diet would look like,” she says. “There’s a suggestion that a Mediterranean diet, for example, may be good for brain health.”
However, she does admit that there are several prevailing theories that could very well explain the connection between elevated blood sugar and dementia. Another factor is the weakening of blood vessels that diabetes causes. This can also put people at risk for ministrokes in the brain which are also linked to dementia.
Excessive sugar intake can cause cells to become insulin resistant, which can cause brain cell death. Plus, eating too much sugar can cause obesity which creates inflammation. And inflammation can also damage the brain. One study linked obesity with elevated amyloid proteins later in life.4
According to Roberts, type 1 diabetics are primarily at risk if they poorly control their insulin and suffer from hypoglycemic episodes. But regardless of whether people have diabetes or not, they should still be watching their sugar intake, she warns.
She says, “just because you don’t have type 2 diabetes doesn’t mean you can eat whatever carbs you want,”. “Especially if you’re not active.” What we eat, is a big factor in maintaining control of our destiny.”
She also says that this new study by Xie, is very eye-opening because it shows the relationship between prediabetes and cognitive decline.
And while there are other factors associated with Alzheimer’s disease like genetics, researchers say that decisions we make about food are one risk factor we can control. And the earlier you decide to limit sugar intake the better, or so it would appear.