As increasing numbers of people with type 1 diabetes live into old age, a large new study has found they face almost three times the risk of developing dementia compared to people without the condition - raising urgent questions about how the disease affects the brain over time.
Author
- Craig Beall
Associate Professor in Experimental Diabetes, University of Exeter
To put this in context, of the 283,772 people in the study , 5,442 had type 1 diabetes. Of those, 144 people went on to get dementia. That is 2.6% of that group.
Of those without diabetes, only 0.6% went on to develop dementia. Once the researchers had accounted for factors like age and education level, the overall increased risk was about three times higher.
A similar trend appeared for type 2 diabetes. Those people had roughly a twofold higher risk.
It is important to note that this data was taken from a health registry. This gives imperfect data, as some people will have undiagnosed diabetes and others will be misdiagnosed with the wrong type of diabetes. Some dementia cases may also have been missed. The follow-up period in this study was also relatively short at roughly two and a half years.
However, the data follows trends similar to that seen in a smaller Swedish study, published in 2025 . In this study, those with type 1 diabetes had a roughly twofold higher risk of dementia. This study also had a longer follow-up of 14 years.
Why type 1 diabetes, specifically?
This raises the question of why type 1 diabetes appears to carry a higher risk of dementia. There are a number of reasons, including that those with type 1 diabetes may have lived with diabetes for more years than type 2 diabetes. Type 1 diabetes can occur in younger people, and having a chronic disease for more years increases the risk for other conditions.
There is also the rollercoaster of blood sugar levels. The peaks and troughs are typically more extreme in type 1 diabetes.
It is particularly the low blood sugar levels that are dangerous. Very low blood sugar can harm the brain by putting stress on its nerve cells. Those with type 1 diabetes have roughly twice as many bouts of low blood sugar compared to type 2 diabetes.
Also, after a low, rapid and extreme high blood sugar further worsens brain cell health. A recent study in mice found that having high blood sugar after a low blood sugar episode may cause even more harm - especially to the hippocampus, the part of the brain that helps with learning and memory.
One of the main reasons for the extreme variation in blood sugar seen in type 1 diabetes is insulin. Compared to tablet-controlled type 2 diabetes, multiple daily insulin injections always carry an increased risk of low blood sugar.
Despite careful monitoring and carbohydrate counting, accurately managing blood sugar using insulin is difficult. Patches that continuously monitor blood sugar and insulin pumps (devices that automatically infuse insulin) have helped to reduce but not eliminate hypoglycaemia. However, the link between insulin and dementia runs deeper.
The insulin connection
Insulin levels are controlled by how much hormone gets made and how quickly it is broken down. In the case of breakdown, this is controlled by a molecule called insulin-degrading enzyme. Despite the name, this molecule also breaks down a protein strongly linked with dementia, called amyloid beta.
If there's too much insulin, the enzyme focuses on insulin first . This means less amyloid beta gets broken down, so it can build up in the brain.
This is bad as amyloid is a sticky protein that clumps together in the brain to make amyloid plaques. These clumps are thought to damage the way brain cells communicate, eventually causing an increasing number of brain cells to die. The brain begins to shrink, impairing cognition.
These plaques are linked strongly with Alzheimer's disease specifically. And type 1 diabetes is associated with an increased risk of developing Alzheimer's .
There is also an increased risk of developing vascular dementia, the type caused by poor blood supply to the brain. This is because high blood sugar damages blood vessels throughout the body, including the brain.
Despite these rather gloomy links, there is cause for some optimism. Diabetes is now more treatable than ever. Many older people with type 1 diabetes have lived with the disease for 60, 70 or even 80 years.
There are many classes of drugs for all forms of diabetes . With combinations, there are over 50 different treatments available.
Some diabetes drugs may lower the risk of dementia. For example, metformin - the main treatment for type 2 diabetes - can reduce dementia risk by more than 10%. It works by helping the body use insulin more effectively.
Whether the brain benefits of this drug also occur in those without diabetes is currently being tested in the Metformin in Alzheimer's Disease Prevention trial . This drug is increasingly used in people with type 1 diabetes, particularly those with reduced insulin sensitivity.
There are mixed results on whether weight-loss drugs reduce dementia risk. A large trial showed limited to no benefit of oral weight-loss drugs on dementia progression in people with mild cognitive impairment and Alzheimer's.
Another study using the weight-loss drug liraglutide, however, showed some benefit. This smaller drug - potentially more able to get into the brain - helped to better protect cognition in people with mild-to-moderate Alzheimer's.
These drugs are increasingly being used in type 1 diabetes, as early evidence suggests they help blood sugar control. Whether this can also protect the brain in type 1 diabetes remains to be determined.
However, physical activity can lower the risk of dementia. A 2025 study found that the more people exercised, the lower their risk of developing dementia. Around 30 minutes of exercise each week decreased risk by about 40%. Those who were the most active, doing over 140 minutes per week, had nearly 70% decreased risk.
Staying active and tailoring diabetes treatment over time may help reduce the higher risk of dementia in people with type 1 diabetes. The continuing progress in stem cell therapies for type 1 diabetes gives further reason for optimism.
Craig Beall currently receives funding from Diabetes UK, Breakthrough T1D, Steve Morgan Foundation Type 1 Diabetes Grand Challenge, Medical Research Council, NC3Rs, Society for Endocrinology and British Society for Neuroendocrinology.
