Why Diabetes and Alzheimer's Are Linked
The long-term effects of impaired glucose processing can take its toll. At the core of this metabolic dysfunction lies insulin, the pancreatic hormone that regulates glucose levels in the blood. Whether it's insufficient production of insulin in type 1 diabetes, or decreased sensitivity of the body's cells to insulin in type 2 diabetes, the result is the same: hyperglycemia, or high blood sugar.
Because prolonged hyperglycemia can affect neurological functioning, diabetes is considered a contributing factor in many cognitive illnesses. And we know that the neurological consequences of diabetes can be dire.
When an overabundance of glucose molecules collect in the blood, they eventually bind to proteins in the inner walls of veins and arteries. That contributes to arteriosclerosis, which in turn increases the risk of diseases like stroke and vascular dementia. In some people, a stroke may trigger Alzheimer’s, while in others vascular dementia and Alzheimer’s may coexist.
The role of insulin
At the same time, cellular respiration—the process through which cells burn glucose to obtain energy—is affected by insulin deficiency. If insulin does not efficiently metabolize glucose molecules, some cells, including brain cells, can literally starve to death, a phenomenon that may help to explain impaired cognitive functioning in some people with diabetes.
Both types of diabetes pose significant risks to cognitive health, but there are important differences between them:
• Type 1 diabetes, the inherited form of the disease, affects approximately 10 percent of all people with diabetes and is characterized by insulin dependency. People with this type of disease are unable to produce insulin, sometimes because of a genetic defect and possibly because of an infection. This form of diabetes is typically detected early, usually in childhood, and can be treated with insulin injections and a carefully managed program of diet and exercise.
• In type 2 diabetes, the most common form of the disease, the pancreas produces enough insulin (and often too much), but the cells that insulin is supposed to affect do not respond to the hormone. Later, as the disease progresses, the pancreas may stop producing insulin altogether. Because obesity and a sedentary lifestyle are two major risk factors associated with type 2 diabetes, the implications of this form of the disease on cognitive health are troubling.
With the obesity epidemic now fully recognized in this country, more people are projected to join the 18 million Americans already diagnosed with type 2 diabetes. Add to this the 40 to 70 million Americans with metabolic syndrome, or prediabetes, and it becomes clear that the risk for serious memory-related illnesses in these populations will continue to rise.