In a nation where obesity is becoming an increasingly serious problem, it's not a surprise that according to the American Diabetes Association, 27% of people aged 65 and older in the US have diabetes and approximately 50% have signs of prediabetes. A February 2015 study in Science Daily has found that diabetic individuals, in particular those with type 2 diabetes, have been shown to have a lower level of cognitive function and a higher risk for Alzheimer’s disease.
We have long known about the link between diabetes and vascular dementia, the second most common cause of dementia (the first being Alzheimer’s disease). However, type 2 diabetes in particular affects the ability of the brain and other body tissues to use sugar and respond to insulin. As the cerebral blood vessels that nourish the brain are damaged by the excess blood sugar, the blood vessels fail to nourish the brain cells effectively thus leading to increased cell mortality and leading to the development of dementia symptoms.
The findings in these recent studies have shown a common pathophysiology between diabetes and Alzheimer’s disease and that Alzheimer’s could be viewed as a new form of diabetes. This can be exhibited by the pathological process amyloidosis, in which “misfolded proteins (amyloids) form insoluble fibril deposits, occurs in many diseases, including Alzheimer disease (AD) and type 2 diabetes mellitus (T2D)” (Elsevier, 2015). Although scientists are still learning about amyloid protein development and interactions, they do know amyloid from the brain can stimulate the growth of fibrils in the pancreas and pancreatic-derived amyloid can be found along with brain-derived amyloid deposited in human brain senile plaques, a hallmark of dementia. These amyloid plaques and neurofibrillary tangles are also seen in the brain autopsies of patients who died with diabetes.
Amyloidosis is a common finding in the pancreas of diabetics and has been attributed to the dysfunction of beta cells, which secrete insulin. Studies have shown amyloid deposits and lower beta cell mass are correlated, as the insulin resistance seen in type 2 diabetes fuels beta cells to secrete more and more insulin. This encourages amyloid deposits to form and leads to the early signs of dementia! Researchers have also identified a reduced expression of certain genes in the early stages of Alzheimer's, which happen to be the genes responsible for insulin and insulin receptor production.
|Neurofibrillary tangles and amyloid plaques in Alzheimer cells|
The most controversial aspect of these findings is the effect of insulin therapy on dementia patients, with some saying it speeds up and others saying it slows down cognitive decline. Pathological findings have shown a combination therapy of insulin and hypoglycemic drugs had the most positive effect of the compounds studied. Nevertheless, the connection between these two diseases is still being studied and hopefully, the research being conducted will give way to new therapeutic strategies that can end this devastating disease for good. My maternal grandmother has both type 2 diabetes and late-stage Alzheimer's disease and the advancements being made in this field right now give me hope that soon enough people with similar afflictions will be living happier, healthier lives.
If you're interested, here is a great TED Talk about the link between diabetes and Alzheimer's Disease. I really enjoyed it.
Posted by Rebecca Quirie (Group C)