Alzheimer’s Disease: The New Diabetes?

When one hears “diabetes,” these words may come to mind: sugar, sedentary lifestyle, and insulin. However, there is one important word missing from that list, and it is, in fact, the name of a form of dementia that affects over three million Americans annually. This progressive condition is known as Alzheimer's disease. Though Alzheimer’s and diabetes were initially believed to be completely unrelated illnesses, researchers have uncovered the startling connection between the two, earning the notorious brain condition the nickname “type 3 diabetes.”

Within the broad umbrella of diabetes, there are two subtypes: type 1 and type 2. Both types involve pancreatic cells, specifically beta cells, which are responsible for producing insulin. In type 1 diabetes, these beta cells are attacked by the body’s own immune system, causing excess glucose (sugar) to build up in the bloodstream. On the other hand, type 2 diabetes develops when insulin becomes less responsive to glucose and less efficient at removing it from the bloodstream, causing it to build up rather than be taken into cells for energy. In Alzheimer’s disease, a similar problem of insulin resistance occurs, but rather than causing problems in the body as a whole, the effects are localized in the brain.

When researchers studied the brains of deceased victims of Alzheimer’s, they observed several of the same abnormalities present in those with diabetes, including reduced levels of insulin in the brain. With diabetes, when a person’s blood sugar levels rise or plummet, the body exhibits the problem through behavioral changes, such as confusion, seizures, and more. However, with Alzheimer’s disease, rather than sending very obvious signs of the problem, the brain’s function and structure decline gradually over time. The researchers also noted that a common finding in Alzheimer’s disease is the deterioration of the brain’s ability to use and metabolize glucose, which has been proven to coincide with, or even precede, a decline in cognitive ability found in Alzheimer’s patients.

This brings up a new question, however: does type 2 diabetes cause Alzheimer’s disease? According to the American Diabetes Association (ADA), at least half of the population with type 2 diabetes will go on to develop Alzheimer’s disease; even having diabetes in the first place may increase a person's risk of developing Alzheimer’s later in life by 65 percent. Nonetheless, researchers still aren’t sure that type 2 diabetes can be generalized as the sole cause of Alzheimer’s. By raising the risk of heart disease and stroke, dementia can often result from reduced blood flow to the brain due to blood clots. Moreover, elevated blood sugar can lead to inflammation, which may damage brain cells and trigger Alzheimer’s. Despite these potential scenarios, other causes unrelated to diabetes can still lead to the development of Alzheimer’s disease, such as genetic or environmental factors. Overall, however, this startling discovery of the correlation between Alzheimer’s and diabetes has shone a new light on potential treatments for the mental disease. Mayo Clinic’s Florida and Rochester campuses recently participated in a multi-institutional clinical study that tested whether a new insulin nasal spray could improve Alzheimer’s symptoms. Nasal insulin has been tested in several Phase 2 clinical trials in patients with mild cognitive impairment or early Alzheimer’s. Researchers were excited to find that both short-term and long-term treatments with nasal insulin resulted in improved memory and everyday function. However, evidence suggests that nasal insulin may not be equally effective in all Alzheimer’s patients, due to one gene-coding protein called Apolipoprotein E (APOE). The response to nasal insulin may vary based on not only the dose but also the form of the APOE gene the patient carries. Despite this, in a study conducted by the U.S. National Library of Medicine-National Institutes of Health, the early intranasal insulin therapy was in fact found to halt the progression of neurodegeneration found in Alzheimer’s patients.

Due to the groundbreaking discovery of the correlation between diabetes and Alzheimer’s disease, researchers are now able to adapt current treatments of the glucose-related disorder to the brain. In addition, this discovery offers some insight into our daily lives. The nutritional lifestyle we decide to live now as teenagers may play a crucial role in the future of our mental health—for better or worse.