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A study of 300,000 U.S. adults over age 50 has linked type 1 diabetes with dementia.

People with type 1 diabetes were nearly three times as likely to develop dementia as those without diabetes.

The study does not prove that diabetes causes dementia but shows a correlation between the two conditions.

A new study has found that people with type 1 diabetes are nearly three times as likely to develop dementia as those without diabetes.

“We have known that type 2 diabetes is linked to an increased risk of dementia,” said study author Jennifer Weuve, a professor of epidemiology at the Boston University School of Public Health, “but this new research suggests that, unfortunately, the association may be even stronger for those with type 1 diabetes.”

Published yesterday in the journal Neurology, the paper analyzed a sample of 283,772 U.S. adults over the age of 50.

A total of 5,442 of them had type 1 diabetes, an autoimmune form of the disease that prevents the body from making the insulin it needs to process sugars; 51,511 had type 2 diabetes, a more common metabolic disorder that causes muscle, liver, and fat cells to stop responding to the insulin the body does produce.

The exact causes of type 1 diabetes are unknown, though genetics and environmental triggers like viruses likely play a role. Type 2 diabetes may also have a genetic component, but it’s strongly associated with lifestyle factors like diet, exercise, and chronic stress.

Three times as likely to develop dementia

The study followed participants for an average of 2.4 years. During that time, 2,348 of them developed dementia: 0.6% of the group without diabetes, 1.8% of the group with type 2 diabetes, and a staggering 2.6% of the group with type 1 diabetes.

After taking into account other risk factors like age and education level (higher education has been connected with a delayed onset of dementia), researchers calculated that participants with type 2 diabetes were twice as likely to develop dementia as those without diabetes. Participants with type 1 diabetes, on the other hand, were nearly three times as likely.

The results were similar regardless of gender or ethnicity. 56.7% of the study group identified as women, 60.3% as non-Hispanic white, and 13.3% as Hispanic or Latino.

Healthier aging for people with type 1 diabetes

The study does have limitations. Because it was based on electronic health records and survey data, some diagnoses may have been missed, or some participants may have been diagnosed with the wrong type of diabetes.

It does, however, replicate the findings of a Swedish study published last year, which found that individuals with type 1 diabetes were twice as likely to develop dementia as those without the disease. That study followed its participants for a longer period of about 14 years.

Neither study proves that diabetes causes dementia. They only establish an association between the two diseases. But they do add evidence to the theory that certain forms of dementia may share underlying biological mechanisms with diabetes.

Alzheimer’s disease is occasionally called “type 3 diabetes” based on the hypothesis that Alzheimer’s is triggered by insulin resistance in the brain. The classification of Alzheimer’s as “type 3 diabetes” is still highly controversial, though, and many diabetics never develop dementia.

What the researchers hope is that their work will inspire further investigation so people with diabetes can live longer, healthier lives.

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“For the growing number of people with type 1 diabetes who are over 65 years old,” says Weuve, “these findings underscore the urgency of understanding the ways in which type 1 diabetes influences dementia risk and how we can prevent or delay it.”

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