Diabetes may greatly raise dementia risk, large U.S. study suggests

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A large U.S. study has linked type 1 diabetes to increased dementia risk. Image credit: tolgart/Getty Images

A new study suggests people with type 1 diabetes may be nearly three times as likely to develop dementia compared with people without diabetes.
Similarly, people with type 2 diabetes may have roughly twice the risk of dementia compared with those without diabetes.
However, the study found an association rather than proof of causation, meaning diabetes was linked to dementia risk but was not shown to directly cause it.

Diabetes describes a group of metabolic conditions that typically result from problems with insulin production, action, or both.

Thus, it is not uncommon for those living with diabetes to experience comorbid conditions, or multimorbidity. This refers to an individual living with two or more chronic, long-term health conditions.

Although the link between diabetes and dementia is not well understood, research has noted that diabetes can increase dementia risk.

Now, a new large cohort study published in Neurology, suggests that people with type 2 diabetes have an elevated risk of dementia, but the risk may be even greater among those with type 1 diabetes.

This highlights the need to better understand the mechanisms connecting diabetes and cognitive decline. However, the researchers caution that the findings show an association rather than a cause-and-effect relationship.

The large cohort study analyzed data from the All of Us Research Program. This is a nationwide U.S. research initiative that links electronic health records with survey data to investigate long-term health outcomes.

Researchers examined whether different forms of diabetes were associated with the development of dementia in adults aged 50 years and older.

Among 283,772 participants included in the analysis, researchers identified 5,442 people with type 1 diabetes and 51,511 with type 2 diabetes. The participants had an average age of 64 years and were followed for an average of 2.4 years.

During the study period, 2,348 people developed dementia. This included 144 of the participants with type 1 diabetes (2.6%), 942 of those with type 2 diabetes (1.8%), and 1,262 of the 226,819 participants without diabetes (0.6%).

After adjusting for factors such as age, sex, race and ethnicity, and education, the researchers estimated that people with type 1 diabetes were nearly three times as likely to develop dementia as those without diabetes.

People with type 2 diabetes were about twice as likely to develop dementia compared with people without diabetes.

Even after adjusting for lifestyle factors, such as smoking and alcohol use, the association remained strong. Participants with type 1 diabetes still had more than twice the risk of dementia relative to those without diabetes.

Study author Annie Pederson, MPH, research fellow at the Boston University School of Public Health, was surprised at the magnitude of the association:

“As life expectancy among people with type 1 diabetes continues to increase, this elevated risk of dementia highlights the importance of understanding the neurologic challenges this population may face with aging, and underscores the need for greater awareness, monitoring, and targeted prevention strategies.”

The researchers also found that increased dementia risk linked to diabetes appeared broadly consistent across demographic groups.

When researchers analyzed the data by sex, type 1 diabetes was associated with higher dementia risk in both females and males.

Women with type 1 diabetes had slightly higher relative risk than men, though both groups showed strong associations.

The elevated risk also appeared across racial and ethnic groups, including non-Hispanic white, Hispanic/Latino, and other ethnic groups.

Type 1 diabetes is far less common than type 2 diabetes, accounting for less than 5% of diabetes cases. However, these findings suggest that type 1 diabetes may play a significant role in dementia risk.

Researchers estimated that about 64.5% of dementia cases among people with type 1 diabetes could be attributed to the condition itself.

However, because type 1 diabetes is relatively rare in the general population, it accounted for roughly 3.9% of dementia cases overall in the study population.

Health experts have long recognized diabetes as a risk factor for dementia, but most studies have focused on type 2 diabetes.

The biological pathways linking diabetes to cognitive decline may differ between these two forms of diabetes.

Type 2 diabetes is often associated with insulin resistance, chronic hyperglycemia, and metabolic complications that may damage blood vessels in the brain or promote protein buildup associated with Alzheimer’s disease.

The researchers propose that recurrent hypoglycemia, inflammation, oxidative stress, and long-term metabolic disruption may contribute to brain changes that increase dementia risk.

Commenting on the possible biological mechanisms at play, Pederson told Medical News Today:

“Individuals with type 1 diabetes are typically diagnosed at younger ages, leading to longer disease duration across the life course, which may add up to higher dementia risk over time. In addition, while type 1 diabetes and type 2 diabetes may share some pathways, type 1 diabetes is biologically distinct and may involve additional mechanisms that should be further studied.”

“While there may be growing interest in whether long-term patterns of blood glucose and episodes of hypoglycemia could play a role in dementia etiology, our study was not designed to examine these mechanisms directly, and more research is needed to better understand how these factors may contribute to dementia risk in people with type 1 diabetes,” Pederson added.

A key aspect of the study was the development of a new algorithm to distinguish between type 1 diabetes and type 2 diabetes using electronic health records.

Diagnostic codes can overlap, and some people with advanced type 2 diabetes may also require insulin. This can make accurate identification of diabetes subtypes in large datasets challenging.

To address this, the researchers created a classification method based on the number of clinical encounters coded as type 1 diabetes.

The approach was validated against two reference standards: self-reported diabetes type and laboratory measures of C-peptide, a marker of pancreatic insulin production.

This method enabled the researchers to analyze dementia risk separately for each diabetes subtype in a very large population.

The researchers noted that the study has several limitations. Diagnoses of both diabetes and dementia were identified using electronic health records and survey data, which may not capture every case.

People with type 1 diabetes may also interact with healthcare systems more frequently, potentially increasing the likelihood that dementia is identified earlier.

Additionally, because the All of Us cohort is not nationally representative and relies partly on convenience sampling through healthcare systems, the findings may not fully generalize to the broader U.S. population.

As a result, the findings should be interpreted cautiously. The study shows a link between diabetes and dementia risk but does not prove that diabetes directly causes dementia.

Further research will be necessary to better understand the biological mechanisms that may connect diabetes to cognitive decline and to identify strategies that could reduce the risk.

“While our findings help clarify the association between type 1 diabetes and dementia risk, important questions remain,” Pederson noted.

“To better understand the elevated risk among those with type 1 diabetes future research should examine the role of co-occurring clinical conditions and other potential ‘modifiable risk factors’ that may help identify subgroups at highest risk,” she added.

“In addition, studies are needed to better understand the biological mechanisms underlying this association and to determine whether targeted prevention or management strategies can reduce dementia risk in individuals with type 1 diabetes. Together, this could inform more personalized approaches to care and prevention,” Pederson told us.

Despite these limitations, the researchers say the findings add important evidence that diabetes subtype matters when assessing dementia risk.

As life expectancy for people with type 1 diabetes continues to improve, more individuals with the condition are reaching older age, which is the strongest known risk factor for dementia. As such, the results of this study may indicate more regular cognitive screenings for those living with type 1 diabetes.

“These findings highlight the need for greater awareness of dementia risk in patients with type 1 diabetes,” Pederson added.

“For clinicians, this may mean considering cognitive health as part of long-term diabetes care, particularly as people with type 1 diabetes are living longer,” she said.

“For individuals with type 1 diabetes, these results suggest an increased risk but not a certainty of developing dementia, and reinforce the importance of ongoing care, monitoring, and management of overall health as they age.”

– Annie Pederson, MPH

“We should be clear, however, that the findings from our study and other studies should press us to better understand how to help delay or prevent the development of dementia in people living with type 1 diabetes,” added Pederson.