Losing Your Sense of Smell May Be a Warning Sign of Alzheimer’s
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Key Takeaways
The APOE e4 gene puts you at high risk for developing Alzheimer’s. A new study suggests that people with the gene are also more likely to also develop a loss of smell around the age of 65.
Changes in smell can be an early sign of neurodegenerative diseases like Alzheimer’s and other dementias.
Experts say that developing a smell test could become part of routine Alzheimer’s screenings.
Loss of sense of smell may no longer be strongly correlated with COVID, but new research ties the phenomenon to a different condition.
A recent study from researchers at the University of Chicago found a possible link between a gene associated with Alzheimer’s disease and the loss of sense of smell at around the age of 65. Based on the findings, the researchers think that losing your sense of smell around that age could be an early warning sign of neurodegenerative disease.
The study included 865 people who were tested at 5-year intervals. The tests looked at their ability to detect odor and asked them what odor they were smelling. A DNA sample was also collected to see which participants carried the APOE e4 gene—a known risk factor for developing Alzheimer’s.
The researchers found that the people who carried the gene were 37% less likely to be able to detect odor at around the age of 65 compared to people who did not carry the gene. At age 75, people with the gene also started to lose the ability to identify odors.
Study author Matthew GoodSmith, MD, told Verywell that the findings “only identified a relative decrease in the ability to detect smell in people carrying the APOE e4 gene.” However, GoodSmith said that the team hopes that the research “will spur more interest in researching the connections between smell loss, cognitive decline, and risk for dementia.”
If you lose your sense of smell, you shouldn’t jump to worrying about Alzheimer’s. Here’s what experts say.
Related: What Causes Loss of Smell and Taste?
Why Would Smell Be Linked to Alzheimer’s?
Researchers already know that decreasing ability to smell is linked to neurodegenerative diseases, including Parkinson’s and Alzheimer’s. Often, the first signs of neuron degeneration happen in the olfactory cortex of the brain—the part that controls your sense of smell.
Zara Patel, MD, an otolaryngologist and smelling disorders specialist at Stanford Health Care, told Verywell that the recent study is just the latest of many that have shown similar findings.
“The very first signs of degeneration in the brain are located in the olfactory cortex, so of course, loss of this sense would be the first sign,” she said.
Your ability to smell starts in the mucus membranes of our nose. Electrical signals are sent through the olfactory nerve directly to the olfactory cortex in the brain, which processes the smell.
The olfactory nerve also sends signals to the parts of the brain responsible for emotions and memories (amygdala and hippocampus, respectively). These connections could explain why certain smells trigger specific emotions and memories.
Research suggests that most people diagnosed with Alzheimer’s have olfactory dysfunction, but why they do is not fully understood. Scientists think that changes to certain neural proteins and neurotransmitters in the parts of the brain that help us smell may play a role in the early stages of the disease.
Other neurodegenerative diseases that can affect the sense of smell include:
Related: ‘Smell Training’ Could Help People Who Lost Their Sense of Smell From COVID
Is Smell Part of Diagnosing Alzheimer’s?
According to the Alzheimer’s Association, there is no single test that can confirm a patient has dementia. Instead, Providers usually have to do a variety of screens, tests, and scans to make an Alzheimer’s diagnosis.
Current tests and screenings for Alzheimer’s include:
Medical history
Physical exam (e.g., check blood pressure, review medications, talk about lifestyle)
Blood and urine lab work
Neurological exam (e.g., reflexes, muscle strength, speech, eye movement)
Brain scans (e.g., MRI, CT scan)
Cerebrospinal fluid tests (e.g., spinal tap)
Although a loss of smell could be an early sign of neurodegeneration, it is not currently included in the screenings for Alzheimer’s and other dementias.
However, that could change. Researchers at the University of Warwick are working on a smell and taste test that could become part of a routine health exam and initial Alzheimer’s screening.
Patel said they are also involved with research that’s looking for ways to test a patient’s sense of smell as part of Alzheimer’s screening.
“My current research is centered around developing a device that could objectively test smell, as the current testing methods are hindered by multiple biases that would affect test outcome,” said Patel. “That is why I consider this research so important. I also hope to be able to use this device in the future to not only record signals from the olfactory nerves but also stimulate the nerves for potential regain of function.”
Related: Loss of Smell No Longer Reliable Sign of COVID
What Else Causes Loss of Smell?
Olfactory dysfunction can be caused by a variety of conditions. In recent years, the most notable has been COVID-19. At times during the pandemic, loss of smell and taste was one of the most common symptoms of the virus.
Patel said there’s a wide range of conditions that can cause you to lose your sense of smell, ranging from fairly harmless to serious:
Older age
Trauma or injury
Allergies
Cold or flu
Congestion
Sinus infection
Nasal polyps
Metabolic disorders
Post viral disorders
Tumors
Related: How a Stroke Affects Your Sense of Smell
Should You See a Provider If You Lose Your Sense of Smell?
You don’t necessarily need to panic if you notice changes to your sense of smell, but it is something to pay attention to.
For example, if you figured your loss of smell was from a recent cold you caught but you get better and your smell has not come back or things are not smelling “normal,” don’t brush it off. You won’t know what’s up with your sense of smell until you see your provider.
It might turn out to be something simple that will get better on its own. If not, you may need to see a provider who is more of a smell expert. If you’re older, know you have the gene that puts you at a higher risk for Alzheimer’s, and you lose your sense of smell, your provider might want you to see a neurologist for more testing.
“People should seek out a physician who is a smell expert for a full evaluation and work-up,” said Patel. “The longer you go with smell loss before definitive intervention, the harder it is to bring that sense back.”
What This Means For You
You don’t need to panic about Alzheimer’s if you lose your sense of smell, but that doesn’t mean you should just brush it off. Let your provider know if your sense of smell has changed, especially if it’s not getting better. If it is a warning sign of something more serious, your provider can help you figure out the next steps.
Read Next: Early Warning Signs of Dementia Checklist
