People at risk of developing Alzheimer’s disease may lose their sense of smell earlier in life than others, according to a new study.
The study does not imply that everyone who loses their sense of smell is at risk for developing Alzheimer’s, but it does add to previous research on the connection between Alzheimer’s and olfaction.
A new study suggests that people at risk for developing Alzheimer's disease may experience a decline in odor sensitivity years before experiencing cognitive decline. The research indicates that impairment or loss of sense of smell can be an early warning sign of the condition.
Researchers followed more than 1,000 older adults for 10 years, periodically testing their genes and ability to smell and think. They found connections between those who carry the APOE e4 gene variant, commonly present in people with Alzheimer’s, and impaired ability to detect smells. Those who carried the gene variant experienced difficulty detecting odors between ages 65 and 69, about a decade before those without the gene. Those with the variant were also, at any given point, 40% less likely to have good odor detection than those without it, according to the study.
Dr. Heather Sandison, ND, neurocognitive medicine specialist and founder and medical director of companies Solcere and Marama, says that the research makes sense given what we know about the olfactory nerve in the brain.
This nerve is “responsible for transmitting signals from our nose to our brain so we can identify everything from our morning coffee to the smell of rain to a dangerous toxin,” she says. If this part of the brain is damaged—which can happen through a condition like Alzheimer’s—she says, there is “potential for our sense of smell to be impacted by that.”
However, Dr. Sandison says it is also important not to jump to conclusions and assume that a stuffy nose foreshadows Alzheimer’s disease.
“If you are experiencing a loss of smell, there are other potential causes, including inflammation caused by COVID, hay fever, or congestion caused by a common cold,” Dr. Sandison adds.
Adding to existing research
This isn’t the first study to note a connection between the development of Alzheimer’s and impairments to a sense of smell. Previous research has noted that olfactory deficits can be early indicators of both Alzheimer’s disease and Parkinson's disease.
“How much smell loss can tell us about Alzheimer's is still being researched,” says Dr. Sumeet Kumar, PhD, former Parkinson’s researcher and founder of the genetic research website GenesWellness. In addition to the impact that Alzheimer’s has on the olfactory nerve, the disease can cause swelling in the brain, which could also impact sense of smell, he adds.
As research continues to unfold, Daniel Morris, founder of My Caring Plan, a resource for seniors and caregivers, says he already sees Alzheimer’s-smell connections in his community.
“Many people may not realize it, but our sense of smell is often the canary in the coal mine when it comes to cognitive decline,” says Morris. “If you can't relish the aroma of your morning coffee or find that your favorite perfume has lost its charm, it might not just be a passing phase or consequence of a blocked nose. It could be an early indication of something much more severe: Alzheimer’s.”
However, Morris adds that many people experience sensory changes with age, with or without an Alzheimer's diagnosis. So, while this study suggests a correlation between the two, it’s not an absolute cause-and-effect relationship adding to a long list of unanswered questions about Alzheimer’s. “That's the catch,” Morris says, “it's not definitive.”
What this means for you
Losses or impairments to a sense of smell around ages 65 to 69 could be an early biomarker of Alzheimer’s disease, according to a new study that builds on previous research regarding the condition's connection to a sense of smell.