Although we often underestimate our ability to smell compared to our ability to see and hear, our sense of smell provides our brain with important information, from detecting potential hazards like smoke to recognizing the sweet smell of cookies.
Researchers from the University of Chicago Medicine have found another reason to appreciate our sniffers. Deterioration of a person’s sense of smell over time may not only predict loss of cognitive function, but also predict structural changes in brain regions important to Alzheimer’s disease and dementia.
The findings, based on a longitudinal study of 515 older adults, were published on July 2 in the Alzheimer’s disease and dementia: Journal of the Alzheimer’s Associationcould lead to the development of smell screening to detect cognitive impairment in patients earlier.
“This study provides another clue to how the rapid decline in smell is a really good indicator of what will eventually happen structurally in certain regions of the brain,” said senior author Jayant M. Pinto, MD, professor of surgery at at the University of Chicago and is an ENT specialist who studies diseases of the nose and sinuses.
It is estimated that more than 6 million Americans suffer from Alzheimer’s disease, which is characterized by memory loss and other symptoms such as mood swings and problems with daily activities. There is no cure for Alzheimer’s disease, but some medications can temporarily slow its symptoms.
Memory plays an important role in our ability to recognize smells, and researchers have long known about the link between smell and dementia. The plaques and tangles that characterize tissue affected by Alzheimer’s disease often appear in areas of smell and memory before developing in other parts of the brain. It is not yet known whether this damage actually causes the deterioration of a person’s sense of smell.
Pinto and his team wanted to see if it was possible to identify changes in the brain that correlate with a person’s loss of smell and cognitive function over time.
“Our idea was that people with a rapidly declining sense of smell would be in worse shape over time — and more likely to have brain problems and even Alzheimer’s disease itself — than people with a slow decline or a normal sense of smell,” she said. Rachel. Pacino, a fourth-year medical student at the Pritzker University in Chicago and lead author of the study.
The team used anonymized patient data from Rush University’s Memory and Aging Project (MAP), a research group founded in 1997 to study chronic conditions of aging and neurodegenerative diseases such as Alzheimer’s disease. MAP participants are seniors who live in retirement or senior living facilities in Northern Illinois and are tested annually for their ability to identify certain odors, cognitive function and signs of dementia, among other health parameters. Some participants also underwent an MRI.
Scientists at UChicago Medicine have found that a rapid decline in a person’s sense of smell during periods of normal cognition predicts many signs of Alzheimer’s disease, including smaller gray matter in brain regions associated with smell and memory, cognitive impairment and an increased risk of dementia in these older adults. . In fact, the risk of losing the sense of smell was similar to carrying the APOE-e4 gene, a known genetic risk factor for Alzheimer’s disease.
The changes were most prominent in key olfactory regions, including the amygdala and the entorhinal cortex, which is the primary input to the hippocampus, a critical site in Alzheimer’s disease.
“We were able to show that the volume and shape of gray matter in the olfactory and memory-related brain regions of people with rapid olfactory decline was smaller compared to people who had less severe olfactory decline,” Pinto said.
An autopsy is the gold standard for confirming someone has Alzheimer’s, and Pinto hopes to eventually expand on those 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 people for signs of early dementia, and to develop new treatments.
Smell tests are an inexpensive, easy-to-use tool that consists of a series of sticks that look like felt-tip pens. Each stick is filled with a special scent that people have to identify from four options.
“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 put them in clinical trials and develop better drugs,” Pacino said.
The study was limited by the fact that the participants only had one MRI scan, which meant the team didn’t have enough data to determine exactly when structural changes in the brain began or how quickly brain regions were shrinking.
“We have to look at our study in the context of all the risk factors we know about Alzheimer’s disease, including the effects of diet and exercise,” Pinto said. “Olfaction and changes in olfaction must be one important component in the context of a number of factors that we believe influence brain health and aging.
Additionally, because the majority of MAP participants were white, more research is needed to determine whether underrepresented populations are similarly affected. The team’s previous work showed marked racial differences, with African-Americans experiencing the most severe olfactory impairment.
Pinto’s previous research has examined smell as an important marker of declining health in older adults. His 2014 paper found that older adults without a sense of smell were three times more likely to die within five years, a better predictor of death than a diagnosis of lung disease, heart failure or cancer.
Other scientists who contributed to “Rapid decline in olfaction during aging predicts dementia and GMV loss in brain regions in AD” include Kristen Wroblewski, M.D., and Martha McClintock, Ph.D., David Lee Schillinglaw Professor Emeritus, Department of Psychology and Comparative Human Development at the University of Chicago, and Duke Hahn, Ph.D., professor of family medicine, neurology, psychology and gerontology at the University of Southern California.