Diabetes and dementia: exploring the links

Studies have linked type 2 diabetes and dementia later in life for a few years, but the link between the two conditions, causative or otherwise, remains unclear.

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

The article, “New Horizons-Cognitive Dysfunction Associated With Type 2 Diabetes,” was published in the high-impact international Journal of Clinical Endocrinology & Metabolism. It also highlights the importance for clinicians to identify and manage treatments in people with type 2 diabetes and cognitive dysfunction.

Professor Velandai SrikanthDirector, National Center for Healthy Aging, was invited by the journal to perform the review. This is a subject that his group has studied a lot. “The connection is not something that is usually talked about, but people have become more aware of it over the last 10 or 15 years,” Professor Srikanth said.

“Several studies showed around 15 years ago that type 2 diabetes is linked to a doubling of the occurrence of dementia in subsequent years – but what could be the cause? diabetes is a cause of the increased risk of dementia or is there another set of mechanisms?”

The answers are important. Type 2 diabetes is very common, affecting approximately 463 million people worldwide. One in five adults over the age of 65 have diabetes, mostly type 2, according to the review.

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

Clinicians will increasingly be tasked with caring for older adults with 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 states.

Written from a clinical perspective assessing information from 164 articles, the narrative review discusses potential mechanisms and pathways linking the two comorbidities, as well as factors such as hyperglycemia, blood pressure and changes in mode of life.

“My theory is that the impact of diabetes, the way diabetes relates to the brain, goes through several pathways, and each of these pathways could contribute a small amount to the overall effect,” Professor Srikanth said. “If you’re just trying to treat one route or a one-way treatment, like blood pressure tablets or a cholesterol tablet, you may not be treating the whole package and therefore treatment may not be successful.”

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

“There may be better ways to capture the effects of diabetes on the brain in the future with much more sensitive measurements of the brain with MRIs or PET scans.”

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

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

The first author is a geriatrician/researcher assistant associate professor Chris Moran.

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

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