A large new observational study finds that the risk for dementia in type 2 diabetes is highest for vascular dementia and among individuals in whom blood sugar is poorly controlled.

Investigators compared health data from more than 370,000 people with type 2 diabetes with nearly 2 million controls over an average of seven years. Individuals with diabetes were 36% more likely to develop vascular dementia and 9% more likely to receive a non-vascular dementia diagnosis compared with their diabetes-free peers, they found. But these individuals’ risk of Alzheimer’s disease was not higher, reported Naveed Sattar, Ph.D., from the University of Glasgow, Glasgow, Scotland.

A 36% higher risk is in itself an argument for preventive measures such as a healthier lifestyle,” Sattar said. “The importance of prevention is underscored by the fact that, for the majority of dementia diseases, there is no good treatment.”

Sattar and colleagues also examined whether blood sugar control had an effect on these associations. Compared with patients with well-controlled blood sugar, study participants with poorly controlled blood sugar had nearly double the risk of developing vascular dementia. (Well-controlled blood sugar was defined as HbA1c of under 52 mmol/mol, and poorly controlled blood sugar was defined as having HbA1c of over 87 mmol/mol.)

In all cases, investigators adjusted the results for a range of dementia risk factors, such as age, sex, education, income, body mass index and pre-existing health measures.

The study does not prove cause and effect, and the absolute risk of developing dementia in diabetes — although increased — is low, the researchers acknowledged. 

“Our findings by no means suggest that most who have diabetes will go on to develop vascular dementia in later life,” says co-author Carlos Celis, Ph.D., also from the University of Glasgow. “But with the number of people with type 2 diabetes doubling over the past 30 years, the importance of a healthy lifestyle is clearer than ever. Moreover … our findings underscore the importance of good blood sugar control.”

The study was presented at the virtual annual meeting of the European Association for the Study of Diabetes, Sept. 21 through 25.