Étienne Aumont is a PhD student in psychology at the University of Quebec in Montreal (UQAM) and Maria Galipeau is a PhD student in molecular biology at the University of Montreal.
Over half a million Canadians are living with dementia in Canada, a cost to society over $ 10 billion annually. Alzheimer’s disease is involved in most of these cases. It is therefore essential to find a treatment.
A theory developed by Suzanne M de la Monte, a professor at Brown University, argues that Alzheimer’s is actually caused by a disruption in the brain’s metabolism. Supported by other researchers, the scientist has suggested renaming the disease “type 3 diabetes”. Although diabetes and Alzheimer’s have many things in common, this proposal undermines the general public’s understanding of Alzheimer’s. Although this information circulates a lot on social media, it is not a widespread theory in the medical and scientific fields.
As a doctoral student in molecular biology working on diabetes and a doctoral student in psychology specializing in Alzheimer’s, this question is at the crossroads of our worlds. We therefore set out to meet the third type … of “diabetes”!
A problem of definition
The term “type 3 diabetes” directly links Alzheimer’s type 1 and type 2 diabetes, two metabolic diseases. Type 1 diabetes is caused by an autoimmune attack on the pancreas, the insulin-producing organ. Deprived of insulin, some cells can no longer feed on glucose, a sugar that is their source of energy. Type 2 diabetes occurs when the pancreas has to produce too much insulin. In the long run, the cells become insensitive to it.
What do these two types of diabetes have in common? The abnormally high concentration of glucose in the blood. However, the definition of Alzheimer’s is totally different. It’s about a toxic accumulation beta-amyloid and tau proteins in plaques and tangles, which can be seen under the microscope.
Alzheimer’s, a metabolic disorder?
In Alzheimer’s disease, neurons receive less and less sugar, which have difficulty entering the brain. Neurons must therefore consume less energy. Like a mountain climber at high altitude, they slow down their metabolism to cope with this energy deprivation. But this is not without consequences. These diseased neurons produce toxic substances, which make them increasingly vulnerable to other problems related to the disease.
Insulin helps neurons work better, so it’s important for keeping the brain healthy. In a person with Alzheimer’s disease, the brain becomes less sensitive to insulin than that it would lead to the loss of cognitive functions like memory and learning. However, unlike type 2 diabetes, where insulin insensitivity is present throughout the body, Alzheimer’s would only affect the brain. This would explain the fact that the consequences of the two diseases are so different.
Suzanne de la Monte then determined that the brain’s insensitivity to insulin and weakened metabolism were the causes of Alzheimer’s. Because diabetes is associated with dysregulation of insulin and glucose levels, she strongly defended her theory that Alzheimer’s should be dubbed “type 3 diabetes”.
A deceptive association
If this theory is correct in all respects, people with type 2 diabetes should be more vulnerable to Alzheimer’s. It is true that diabetes increases the risk of having a cognitive decline. However, these cognitive losses appear to be distinct from those of Alzheimer’s. Diabetes can affect any cognitive function, from attention to language, while Alzheimer’s primarily affects memory. Diabetes and Alzheimer’s therefore appear to affect the brain differently.
On the other hand, the collective imagination strongly associates diabetes with eating habits. For example, we often hear that a high sugar diet increases the risk of suffering from type 2 diabetes. But you should know that a low-sugar, high-fiber diet helps keep blood sugar levels stable for both type 1 and type 2 diabetes. reduces the risk of complications associated with the disease.
Good eating habits also contribute reduce the risk of getting Alzheimer’s, but they probably wouldn’t improve symptoms. By using the name “type 3 diabetes,” we therefore reinforce the unproven idea that diet determines the rate of progression of Alzheimer’s.
New theory, new name?
The metabolic theory is far from the only explanation for the onset of Alzheimer’s disease. Some argue rather than an origin autoimmune, inflammatory or even infectious would be in question. None of these songs managed to stand out. Also, according to a clinical study whose results were published in 2021, insulin inhalation it did not relieve symptoms of people with Alzheimer’s onset.
Certainly, establishing the causes of a disease is essential to finding a cure. However, diseases are generally not named after their cause, but rather according to their manifestation, such as arthritis, diabetes, and cancer.
As such, Alzheimer’s is well known as a disease that leads to memory loss and this knowledge helps make the diagnosis. Renaming the disease would therefore be a big step backwards. We suspect that the proposed name “type 3 diabetes” is rather motivated by the increased notoriety of the metabolic theory of Alzheimer’s.
Such political motivations are harmful both clinically, for the confusion sown in public opinion, and scientifically, for the desire to dominate parallel theories on Alzheimer’s.
