Scientists from the University of Chicago found not only can a decline in a person’s sense of smell over time predict their loss of cognitive function, but it can also foretell structural changes in regions of the brain important in Alzheimer’s disease and dementia.
The finding could lead to the development of smell-test screening to detect cognitive impairment earlier in patients.
The research is published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association and was conducted by Jayant M. Pinto et al.
It’s estimated more than 6 million Americans have Alzheimer’s disease, which is characterized by memory loss and other symptoms, such as mood changes and trouble completing everyday tasks.
Memory plays a critical role in our ability to recognize smells, and researchers have long known a link between the sense of smell and dementia.
The plaques and tangles that characterize tissue affected by Alzheimer’s disease often appear in olfactory and memory-associated areas before developing in other parts of the brain.
It’s still unknown if this damage actually causes a decline in a person’s sense of smell.
In the study, the team examined 515 older adults. They tapped anonymized patient data from Rush University’s Memory and Aging Project (MAP).
The UChicago Medicine scientists found that a rapid decline in a person’s sense of smell during a period of normal cognition predicted multiple features of Alzheimer’s disease.
This included smaller gray matter volume in the areas of the brain related to smell and memory, worse cognition and higher risk of dementia in these older adults.
In fact, the risk of sense of smell loss was similar to carrying the APOE-e4 gene, a known genetic risk factor for developing Alzheimer’s.
The changes were most noticeable in the primary olfactory regions, including the amygdala and entorhinal cortex, which is a major input to the hippocampus, a critical site in Alzheimer’s disease.
An autopsy is the gold standard for confirming whether someone had Alzheimer’s, and the team hopes to eventually extend these findings by examining brain tissue for markers of Alzheimer’s.
The team also hopes to study the effectiveness of using smell tests in clinics—in ways similar to how vision and hearing tests are used—as a means of screening and tracking older adults for signs of early dementia and to develop new treatments.
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