Rapid Loss of Smell Linked with Dementia and Brain Changes

Our sense of smell can bring us plenty of enjoyment, from taking in the scent of the trees on a camping trip to being transported back to childhood when we get a whiff of a favorite dish. It’s important for our safety, too, as certain smells alert us to danger. A new study has also found that the rapid loss of our sense of smell may have implications on our brain health and dementia risk.

Researchers from University of Chicago Medicine examined the brain differences between older adults who had rapidly lost their sense of smell and those who had not. According to their findings, published in The Journal of the Alzheimer’s Association, such a loss can be predictive of cognitive issues and lead to changes in areas of the brain associated with Alzheimer’s.

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Jayant M. Pinto, senior author and professor of surgery at the University of Chicago, says, “This study provides another clue to how a rapid decline in the sense of smell is a really good indicator of what’s going to end up structurally occurring in specific regions of the brain.”

To understand the structural changes, the team used data from 515 older adults who had taken part in Rush University’s Memory and Aging Project. The aim of the project is to understand chronic conditions related to age and neurodegenerative diseases. Participants have annual exams that include tests of their smell and cognitive function. They may also receive MRIs. With this information, Payant’s team investigated whether there were identifiable changes in the brain related to loss of smell that were also linked with cognitive function.

Rachel Pacyna, lead author and University of Chicago medical student, says, “Our idea was that people with a rapidly declining sense of smell over time would be in worse shape – and more likely to have brain problems and even Alzheimer’s itself – than people who were slowly declining or maintaining a normal sense of smell.”

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So what did they find? Something similar to this hypothesis. Their research showed that when a person experienced a swift decline in their ability to smell during a period of normal cognitive health, this was a strong predictor of developing Alzheimer’s features, including smaller gray matter in areas of the brain linked with smell and memory. There was also a decline in cognitive function and a risk of Alzheimer’s similar to those with the genetic risk factor APOE-e4.

This builds on past research showing a link between smell and dementia, with Alzheimer’s-related plaques and tangles often found in olfactory-associated areas of the brain before they’re found in others.

The team says these findings show that smell tests could be a helpful tool in identifying dementia and possibly treating higher-risk patients.

Pacyna says, “If we could identify people in their 40s, 50s and 60s who are at higher risk early on, we could potentially have enough information to enroll them into clinical trials and develop better medications.”

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The team hopes to study this idea going forward.

One limitation of the current study was that participants only had one MRI, meaning it was difficult to determine when changes to the brain occurred and how quickly they happened.

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