Diabetes and dementia: exploring the links

Professor Velandai Srikanth and Associate Professor Chris Moran
tease out the connections between type 2 diabetes and dementia in
their recent review. See also a recent video presentation from them.

by Anne Crawford

Studies have linked type 2 diabetes with dementia in later life for some years but the connection between the two conditions, causal or otherwise, is still to be clarified.

A review by researchers from the Department of Geriatric Medicine, Peninsula Health and Medicine, Central Clinical School has highlighted the need to further explore the potential mechanisms and pathways linking the two conditions.

The article was published in the high-impact international ‘Journal of Clinical Endocrinology & Metabolism’. ‘New Horizons-Cognitive Dysfunction Associated With Type 2 Diabetes’ also stresses the importance of clinicians identifying and managing treatments in people with coexistent type 2 diabetes and cognitive dysfunction.  

Professor Velandai Srikanth, Director, National Centre for Healthy Ageing, was invited by the journal to conduct the review. It’s a subject his group has researched extensively. “The link is not something that’s usually talked about but people have become more aware of it in the last 10 or 15 years,” Professor Srikanth said. 

“Several studies showed around 15 years ago that type 2 diabetes is linked to a two-fold increase in the occurrence of a dementia in later years – but what might be the cause? Is it that the diabetes is a cause in the increasing risk of dementia or is there another set of mechanisms?”

The answers are important. Type 2 diabetes is highly prevalent, affecting around 463 million people globally. One in five adults older than 65 years have diabetes, mostly type 2, the review says. 

Increasing age is also associated with an increased incidence and prevalence of cognitive dysfunction and dementia. In 2015, an estimated 46.8 million people lived with dementia globally with this number expected to double every 20 years. 

Clinicians will be increasingly tasked with managing older people who have both type 2 diabetes and cognitive dysfunction. There is also great research interest in whether type 2 diabetes is a direct causal factor in the pathogenesis of cognitive decline and dementia, the review says.

Written from a clinical perspective assessing information in 164 papers, the narrative review discusses potential mechanisms and pathways linking the two co-morbidities, and factors such as high blood glucose, blood pressure and lifestyle modifications. 

“My theory is that the impact of diabetes, the way diabetes is related to the brain, is through multiple pathways, and each of these pathways might have a small amount to contribute to the overall effect,” Professor Srikanth said. “If you’re just going to try dealing with one pathway, or one treatment addressing a single pathway such as blood pressure tablets or a cholesterol tablet, then you might not address the whole package and hence treatment might not be successful.”

Advances in technology measuring brain dysfunction will help in understanding potential mechanistic pathways and guide recommendations for clinical practice, the review says.

“There might be better ways to capture the effects of diabetes on the brain going forward with much more sensitive measurements of the brain with MRI or PET scans.” 

Professor Srikanth said he hoped the article would help inform clinicians about the issues involved in treating people with the co-morbidities. 

Challenges for researchers and clinicians in the future include developing: testable frameworks for the early identification of people with type 2 diabetes at risk of future cognitive problems; implementable and sustainable clinical response models of care for such people to prevent future cognitive decline; and a strong evidence base for the ideal management of diabetes and its complications in those with prevalent cognitive dysfunction or dementia.

First author is Geriatrician/Researcher Adjunct Associate Professor Chris Moran.

To read a previous review on the topic in which Professor Srikanth was first author, see Lancet Diabetes and Endocrinology.