Could Changes In Smell Be An Early Warning Sign of Alzheimer’s?

Based on a new study, being unable to distinguish between certain smells, such as petrol and bubble gum, could be an early indication of Alzheimer’s. As the olfactory neurons become damaged, reduced odor identification may be a clear biomarker. These findings have recently been published in the journal, Neurology, and may one day support the diagnostic process.

How Alzheimer’s Influences the Olfactory System

Before we dive into the latest research, let’s discuss the connection between Alzheimer’s and your sense of smell. Since Alzheimer’s is a degenerative condition, the affected population experiences symptoms across varying phases. As damage to the brain expands, new, progressive symptoms arise.

Throughout stages 1-2, for instance, this disease is often referred to as clinically silent. Although memory and learning will begin to suffer, non-cognitive changes will also develop, including potential olfactory issues. Since olfaction and memory are so closely related in terms of the limbic system, this is why particular smells evoke emotion.

Have you ever personally experienced this?

When detecting a certain smell, you’re transported to a specific time or memory? That’s because previous experiences can be triggered by an olfactory stimulus, including our ability to learn. Although our ability to smell diminishes with age, medical causes can also affect this sensation.

Throughout years of research, the link between Alzheimer’s and the loss of olfaction is clear. Although it’s unknown why this occurs in Alzheimer’s patients, various theories have developed. Two of the core theories include:

  • The Olfactory Vector Theory — Developed in 1985, it’s possible that the olfactory system acts as a gateway for various triggering agents. Meaning, loss of smell may be due to the transport of virus or toxins traveling from the nose to the brain.

  • The Secondary Degeneration Theory — Since the limbic system is particularly susceptible among those with Alzheimer’s disease, loss of olfaction may be due to retrograde secondary degeneration.

Study Finds — Changes In Smell May Indicate the Early Stages of Alzheimer’s

As mentioned, for over 30 years, scientists have been exploring the possible connection between the difficulty in identifying various scents and memory loss. Based on the areas that are initially damaged by Alzheimer’s, involving your ability to smell and name odors from memory, this connection is sparking new areas of research.

Within this new study, researchers from McGill University wanted to test their theory regarding changes to the olfactory system. Researchers studied 274 healthy participants who were considered to be ‘high risk’ for developing Alzheimer’s, based on the fact that they had a parent who had suffered from this degenerative disease.

During the study, each participant was given a multiple choice, scratch-and-sniff test in order to identify various scents. These included strong smells, such as lemon, petrol and bubble gum. Of these participants, one hundred of them had also volunteered to have lumbar puncture tests, measuring levels of AD-related proteins in their cerebrospinal fluid.

What they found, was that:

  • A reduction in odor identification was associated with lower cognitive score and older age, as well as an increased ratio of tau and β-amyloid.
  • Among healthy high-risk individuals, odor identification reflects a potential degree of preclinical Alzheimer’s pathology.
  • Diminished odor identification may be an affordable and practical biomarker of Alzheimer’s.

Of course, there is still more research that needs to be conducted, but based on the current evidence, an odor detection test may support future diagnostic processes. When combined with paper tests or the BrainTest app, for instance, by conducting olfactory tests, symptoms may be more clearly identified as a sign of Alzheimer’s.

Related Studies That Link Sense of Smell to Alzheimer’s

Since this connection has been explored for decades, this isn’t the first study to verify such a link. Although many researchers have been skeptical that a simple ‘smell test’ could help diagnosis such a complex disease, it’s hard to ignore the research.

Based on previous research, here are some additional findings:

  • At the University of Florida, a ruler and a spoonful of peanut butter were shown to be effective tools in terms of confirming the early stages of Alzheimer’s. A graduate student had noticed that while shadowing in the clinic, patients were not being tested for their sense of smell. When testing her theory, it was found that patients who were in the early stages of Alzheimer’s, struggled to detect the distinct smell of peanut butter.
  • Within a longitudinal study, it was found that people aged 41 to 85 years old, who had lost their sense of smell, experienced a 50 percent chance of developing Alzheimer’s.
  • After studying 183 patients at Massachusetts General Hospital, the lead investigator stated that a diminished sense of smell caused by Alzheimer’s, may be detected as early as a decade before symptoms of memory loss surface.

At the end of the day, one of the most important aspects of treatment is early intervention. If a more conclusive test was developed, it’s possible that patients could intervene years before significant cognitive issues develop. By then, researchers may better understand this disease, helping patients reverse poor brain health and future cognitive decline.

Suggested reading: The Memories of Alzheimer’s Patients May Not Be Gone Forever

If you are currently concerned about potential early warning signs, it is important that you take action. Our scientifically-validated app can help you detect early warnings signs of Alzheimer’s. Try it for free today!

Krista Hillis has a B.A.Sc degree, specializing in neuroscience and psychology. She is actively involved in the mental health and caregiving community, aiming to help others. Krista is also passionate about nutrition and the ways in which lifestyle choices affect and influence the human brain.

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