Untreated diabetes and dementia are closely linked. Research shows that when blood sugar remains high for long periods and diabetes is not well controlled, the risk of dementia, including Alzheimer’s disease, rises clearly above that of people without diabetes or with well managed diabetes.
Doctors have known for years that type 2 diabetes is not only a problem of blood sugar, but a condition that affects blood vessels, nerves, and many organs, including the brain. A large body of research shows that people with type 2 diabetes are more likely to develop cognitive problems, such as trouble with memory, attention, processing speed, and planning, which can progress to full dementia over time, especially if the diabetes is poorly treated. One narrative review notes that keeping blood sugar near normal helps preserve thinking abilities, while untreated or inadequately treated diabetes increases the risk of dementia by worsening brain function over the years. You can see this discussed in articles such as https://pubmed.ncbi.nlm.nih.gov/41480353/ and https://pmc.ncbi.nlm.nih.gov/articles/PMC12753325/.
In type 2 diabetes, the body either does not make enough insulin or does not respond to it well. This leads to chronic hyperglycemia, which means blood sugar is frequently or constantly higher than normal. Over years, this long term high sugar damages both large and small blood vessels. The same process that increases the risk of heart attack and stroke also affects brain circulation. Narrowed or diseased blood vessels can limit blood flow to parts of the brain, contributing to what doctors call vascular cognitive impairment and vascular dementia. Reviews like the one at https://pmc.ncbi.nlm.nih.gov/articles/PMC12753325/ describe how diabetes related vascular disease and inflammation are key pathways connecting diabetes to dementia.
Untreated or poorly controlled diabetes also seems to harm the brain in ways that go beyond blood flow. High sugar levels and insulin resistance can increase oxidative stress and chronic inflammation in brain tissue. These changes may make it easier for abnormal proteins like amyloid and tau, which are tied to Alzheimer’s disease, to build up. Some researchers even use the term “type 3 diabetes” to describe Alzheimer’s disease because of these similarities. Popular summaries, such as those on brain effects of “type 3 diabetes,” explain that people with diabetes have significantly higher rates of Alzheimer’s and other dementias, and that the risk is especially high when blood sugar is not well controlled. This is reflected in articles like https://gulfnews.com/lifestyle/could-type-3-diabetes-harm-your-brain-what-your-blood-sugar-levels-mean-for-alzheimers-risk-1.500377397 and https://www.timesnownews.com/health/is-type-3-diabetes-hurting-your-brain-what-blood-sugar-levels-mean-for-dementia-risk-alzheimers-disease-insulin-resistance-article-153288602.
Epidemiological studies, which follow large groups of people over time, repeatedly show that diabetes is a clear risk factor for dementia. Meta analyses and population studies find that people with diabetes have a higher chance of both Alzheimer’s disease and all cause dementia when compared with those who do not have diabetes. Some reports summarized in lay outlets mention figures like a more than 70 percent higher risk of dementia among people with diabetes, with the risk climbing further in those who have had diabetes for many years or whose blood sugar is poorly managed. The relationship between worse glycemic control and higher dementia risk is discussed in sources such as https://gulfnews.com/lifestyle/could-type-3-diabetes-harm-your-brain-what-your-blood-sugar-levels-mean-for-alzheimers-risk-1.500377397 and https://nuffieldclinic.com/could-your-blood-sugar-be-affecting-how-you-think-remember-and-decide/.
On top of this, major dementia prevention reports now list diabetes as one of the key “modifiable risk factors” for dementia. The Lancet Commission on dementia prevention highlights diabetes alongside high blood pressure, hearing loss, smoking, physical inactivity, and other factors that can be addressed to lower overall risk. An example of how important these risks are can be seen in summaries of the Commission’s work, such as the Trinity College Dublin report on dementia prevention, which notes that addressing modifiable factors, including diabetes, could prevent a substantial share of dementia cases in a population. This kind of discussion appears in overviews like https://www.tcd.ie/medicine/research/news/2025/study-identifies-powerful-opportunity-to-act-on-dementia-prevention/.
The duration and quality of diabetes treatment matter a great deal. People with short term, newly diagnosed diabetes who quickly get their blood sugar under control seem to have a lower added risk than those who spend years with high sugar levels or skip treatment. Poor control often shows up as a high HbA1c value, which reflects average blood sugar over several months. Clinical and observational work suggests that higher HbA1c values are associated with faster cognitive decline and greater dementia risk, while better glycemic control relates to more stable thinking skills. Educational articles for patients, such as the one at { lazyloadBackgroundObserver.observe( lazyloadBackground ); } ); }; const events = [ 'DOMContentLoaded', 'elementor/lazyload/observe', ]; events.forEach( ( event ) => { document.addEventListener( event, lazyloadRunObserver ); } );