Can Diabetes Cause Alzheimer's Disease? A Look at the Connection Between Blood Sugar and Dementia

A growing number of studies show that people with diabetes have a greater chance of developing dementia as they get older. Sometimes referred to as “type 3 diabetes” in recent research, dementia is caused by abnormal brain changes that decrease memory retention and cause dysfunction in the way neurons communicate with each other.

Over time, these changes impair the brain’s capacity to process thoughts, leading to changes in behavior and the ability to complete everyday tasks. Research has shown that diabetes is a significant risk factor for the two most common types of dementia: vascular dementia and Alzheimer’s disease. 

In this article, learn more about the characteristics of these two types of dementia, the link between diabetes and dementia, and the best ways to reduce the risk of both diseases. 

Vascular Dementia Vs. Alzheimer’s Disease

Scientists are not entirely clear on how diabetes increases the risk of dementia. One possible explanation is that excessive blood sugar damages the blood vessel network that runs through the body. Chronically high blood sugar will slowly deteriorate the cardiovascular system and, ultimately, damage the brain. 

Blood vessels in the brain and nervous system are especially susceptible to these changes. These damaged vessels become occluded or “leaky,” causing inflammation that further damages the nervous tissue and develops into vascular dementia. 

However, the most common form of dementia is Alzheimer’s disease. In this type of dementia, abnormal proteins called amyloid accumulate inside neurons, impairing neural functioning and damaging brain cells. 

Plaque deposits further damage the brain.  Eventually, these clusters of damaged neurons atrophy and shrink. In one study that used MRI imaging, researchers compared the brains of healthy people against people with type 2 diabetes. Although neither group had dementia, those with diabetes had smaller brain volumes and more signs of atrophy in the hippocampus, the area of the brain associated with memory. 

Another study, published in Neurology in June 2002, showed that the brains of people with diabetes had more amyloid protein plaques and deposits than brains of healthy people. As the extent of this brain damage correlated with the amount of Alzheimer’s-related cognitive decline, the researchers concluded that these abnormal changes could all be linked to diabetes. 

It is important to keep in mind that in most cases, dementia is a result of a mixed series of events — there isn’t just one sole cause. Patients with dementia may have characteristics of both of the main types. This means that vascular dementia patients may have some plaque and amyloid, while Alzheimer’s patients may have some vascular abnormalities. 

As dementia is the result of several different processes occurring over time, it is essential to know the risk factors of the disease to establish the best preventive strategies.

Risk Factors for Diabetes and Dementia

Diabetes is a known risk factor for strokes and small vessel disease, the hallmarks of cardiovascular disease. Strokes occur when the walls of small blood vessels become leaky or occluded. This disruption in blood flow results in neuron death and increased inflammation, causing the damage to spread further.

Over time, clusters of mini-strokes accumulate and lead to vascular dementia. The effect of chronically high blood sugar has a compounding effect on the vessels in the brain. Damage to these vessels disrupts the availability of oxygenated blood to the brain. This cumulative damage eventually compromises brain function and can lead to Alzheimer’s disease and dementia, as discussed in a February 2017 review. 

Therefore, reducing cardiovascular risk factors may be one of the best ways to reduce the risk of both dementia and diabetes. 

These risk factors include:

• Obesity
• High blood sugar
• Abnormal cholesterol and lipid levels
• High blood pressure

Improving these markers may preserve blood vessels and brain integrity, thereby reducing the risk of dementia.

Alzheimer’s Disease and High Blood Sugar

There is less evidence that supports the reduction of cardiovascular risk factors to prevent Alzheimer’s disease. However, research has shown that high blood sugar levels are linked to increased plaque and amyloid accumulation in brain tissue. 

Researchers believe that these risk reduction strategies may reduce some of the cognitive decline attributed to Alzheimer’s disease. Optimal management of these risk factors in early life could provide cognitive benefits in later life for people who have diabetes.

Key Takeaway:

Diabetes is a chronic disease that can significantly increase the risk of dementia, which includes vascular dementia and Alzheimer’s disease. Elevated blood sugar can lead to detrimental changes in the nervous and cardiovascular systems that eventually damage enough brain tissue to develop dementia. 

Changes to the brain caused by high blood sugar take time to develop, with many of these changes taking place over a period of years or even decades. Because of this, researchers recommend that dementia prevention starts as early in life as possible, with a particular focus on reducing known cardiovascular risk factors and keeping blood sugar levels within normal ranges.

References:

den Heijer T, Vermeer SE, van Dijk EJ, et al. Type 2 diabetes and atrophy of medial temporal lobe structures on brain MRI. Diabetologia. 2003;46(12):1604-1610. doi:10.1007/s00125-003-1235-0

Ninomiya T. Diabetes mellitus and dementia. Curr Diab Rep. 2014;14(5):487. doi:10.1007/s11892-014-0487-z

Mankovsky BN, Ziegler D. Stroke in patients with diabetes mellitus. Diabetes Metab Res Rev. 2004;20(4):268-287. doi:10.1002/dmrr.490

Nguyen TT, Ta QTH, Nguyen TKO, Nguyen TTD, Giau VV. Type 3 Diabetes and Its Role Implications in Alzheimer's Disease. Int J Mol Sci. 2020;21(9):3165. Published 2020 Apr 30. doi:10.3390/ijms21093165

Pfeifer LA, White LR, Ross GW, Petrovitch H, Launer LJ. Cerebral amyloid angiopathy and cognitive function: the HAAS autopsy study. Neurology. 2002;58(11):1629-1634. doi:10.1212/wnl.58.11.1629

Serlin Y, Levy J, Shalev H. Vascular pathology and blood-brain barrier disruption in cognitive and psychiatric complications of type 2 diabetes mellitus. Cardiovasc Psychiatry Neurol. 2011;2011:609202. doi:10.1155/2011/609202