Loss of smell could be warning sign for future Alzheimer’s disease, researchers say

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Loss of the sense of smell could be a warning sign of future Alzheimer’s disease, as a recent study published in Neurology, the medical journal of the American Academy of Neurology, noted.

Those who carry the APOE4 gene have a higher risk of both developing Alzheimer’s and of losing the ability to detect odors, the findings stated.

"Testing a person's ability to detect odors may be a useful way to predict future problems with cognition," said study author Matthew S. GoodSmith, M.D., of the University of Chicago, in the journal entry discussing the findings. 

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"While more research is needed to confirm these findings and determine what level of smell loss would predict future risk, these results could be promising, especially in studies aiming to identify people at risk for dementia early in the disease," he also said. 

In the study, more than 865 participants completed two home surveys, taken five years apart, that measured their ability to detect and identify odors. 

Loss of a sense of smell could be a warning sign of future Alzheimer’s disease, as a recent study published in Neurology, the medical journal of the American Academy of Neurology, revealed. (iStock)

At the same intervals, they also took skill tests to gauge their memory and cognitive function.

The participants also submitted DNA samples so the researchers could determine whether they carried the APOE4 gene.

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Those who had the gene variant were 37% less likely to detect odors than those who did not, the researchers found. 

Reduced sense of smell was first noticed between the ages of 65 and 69. 

That group also showed "more rapid declines in their thinking skills," the study findings stated.

"Testing a person's ability to detect odors may be a useful way to predict future problems with cognition," said the author of a new study.  (iStock)

"Identifying the mechanisms underlying these relationships will help us understand the role of smell in neurodegeneration," GoodSmith said.

The study did not include people who had severe dementia.

"These results could be promising, especially in studies aiming to identify people at risk for dementia early in the disease."

Dr. Shailaja Shah, a geriatric psychiatrist at the Carrier Clinic, a behavioral health campus that is part of Hackensack Meridian Health in New Jersey, did not participate in the research but reviewed the findings.

"Olfaction, or the sense of smell, declines with normal aging," she told Fox News Digital. 

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"However, to date, there are quite a few studies that indicate olfaction declines early on in neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and frontotemporal dementia, to name a few."

The most common type of dementia, Alzheimer’s disease affects more than six million people in the U.S., according to the Alzheimer’s Association. (iStock)

"We also know that pathological changes, including plaques and tangles, occur a few decades prior to clinical symptoms and signs of Alzheimer’s disease."

Shah emphasized the need for a non-invasive test and biomarker to detect and diagnose Alzheimer’s disease in its early stages — as well as a clinical, easily available, inexpensive test to study the efficacy of drugs to treat dementia.

Although the APOE4 gene is a risk factor for developing Alzheimer’s disease, not all people with the gene will develop dementia.

"More studies are needed to determine the specificity and sensitivity of an olfactory test in the diagnosis of Alzheimer’s disease, because many other conditions can contribute to a decline in olfaction, such as sinus infections, smoking, side effects of certain medications and COVID, to name a few," she said.

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Although the APOE4 gene is a risk factor for developing Alzheimer’s disease, Shah pointed out that not all people with the gene will go on to develop dementia.

Alzheimer's disease is the most common type of dementia, affecting more than six million people in the U.S., according to the Alzheimer’s Association.

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It is expected that this number will exceed 12 million by 2050.