Celebrated as National Alzheimer’s Disease Month, the month of November is recognized as a nationwide opportunity to raise awareness for those afflicted with the disease. Currently, there are an estimated 5.8 million Americans living with Alzheimer’s disease (AD) – the 6th leading cause of death in the nation. Alzheimer’s disease has seen a dramatic increase in mortality rate of 145% since the year 2000 and continues to grow in incidence.
Although AD mostly affects individuals over the age of 65, early-onset Alzheimer’s may be more prevalent than previously thought, occurring at a rate of close to 6%, rather than the 1-2% rate presumed from prior studies. The number of Americans suffering from Alzheimer’s is growing quickly; projections forecast that by 2050 the number of people living with AD in the United States will grow to approximately 14 million.
As a result, there is an urgent need for improved prevention methods, increased research efforts, and optimized care strategies for AD patients to help serve the growing aging population. In an attempt to enhance screening and treatment methods, researchers continue to analyze the many plausible underlying mechanisms of the disease, and more recently its potential connection to another widespread chronic condition – type 2 diabetes. Emerging evidence implicates the possible connection between Alzheimer’s disease and type 2 diabetes, which affects over 30 million Americans today.
The Link Between Alzheimer’s Disease and Type 2 Diabetes
At the annual meeting of the Society of Neuroscience, Neuroscience 2019, the latest preliminary research was presented exploring this connection further. Researchers currently believe that the underlying link between AD and diabetes is a function of the brain’s metabolism of blood glucose, as well as the many factors that influence the process, including nutrition and sleep habits, physical activity levels, and cardiovascular health.
As part of the session, representatives of the University of Eastern Finland presented a study of the Western diet and its effect on brain insulin. The study revealed that the typical American diet – high in fat and rich in carbohydrates – can decrease brain insulin signaling, which resulted in memory loss in mice genetically prone to Alzheimer’s disease.
Furthermore, insulin signaling was found to play a central role in blood glucose management, aiding the brain in monitoring and controlling insulin release, a finding which supports previous research and confirms the link between impaired insulin signaling and the progression of AD. In the trial, a typical Western diet led to the worsening of age-related memory impairment in mice, suggesting that such nutritional habits may impede the brain’s metabolic processes and act as a trigger for cognitive decline in individuals predisposed to Alzheimer’s disease.
Additional research presented by the University of Arkansas for Medical Sciences revealed that AD mimics diabetes by impairing how the brain metabolizes blood sugar. In examining mice genetically altered to develop Alzheimer’s, investigators discovered that a flaw in glucose delivery to neurons left extra glucose in the blood. As a result, mice with AD showed diabetic traits even whilst consuming a normal diet and maintaining the same physical activity levels and feeding patterns, further confirming the relationship.
The final study from Wake Forest School of Medicine revealed a connection between glucose resistance and abnormal sleep patterns which appear in mice predisposed to Alzheimer’s prior to the appearance of any other AD symptoms, including signs of cognitive decline. Their results implicate the early adverse effects of sleep loss and its association with Alzheimer’s development. Furthermore, poor sleeping patterns in patients with type 2 diabetes may exacerbate AD risk for those already genetically predisposed to dementia.
Thus far, most research on the connection between Alzheimer’s and type 2 diabetes has been conducted in animal models, making it difficult to determine whether any of these results can be applicable to humans. To date, there is limited knowledge of the connection between dementia and brain metabolic processes, however, future research efforts may help illuminate the potential strategies for manipulating these functions to increase treatment efficacy and better identify the precursors of disease.
Preliminary studies presented at this year’s Neuroscience meeting offer a strong starting point for further exploration of the link between two diseases with a high population health burden. However, researchers note that cause and effect across these studies remains unclear. It is unknown whether diabetes is a precursor to Alzheimer’s or if impaired blood sugar metabolism is correlated with AD. Understanding the underlying association between Alzheimer’s disease and type 2 diabetes could help improve early detection strategies and prevention protocols, as well as result in better treatment protocols for both diseases – having wide-reaching positive implications for population health.