How good is your sense of smell?

For over three decades, scientists have been interested in this question because the answer can indicate your risk for Alzheimer’s.

Back in the 1970s researchers discovered that loss of smell went hand in hand with neurodegenerative conditions. In the decades that followed, further research showed this is one of the earliest symptoms of Alzheimer’s disease.

A couple of years ago, Dr. Jacob Teitelbaum told us this when we interviewed him in our 12-part video series “Awakening from Alzheimer’s”. Here’s what he said:

“There’s a test that they’re doing now where you simply take some peanut butter, and you see at what point you can smell it. So you go ahead, pinch your right nostril shut, hold the peanut butter perhaps 10 or 12 inches from your nose, and just slowly move it closer and closer to your left nostril and see when you can start to smell it. Most people can start to smell it at eight inches away. So take a little ruler; see how far it is.

“See when you first notice the smell. Then, go with the other side, the right nostril, and see where you first notice the smell. In people with Alzheimer’s it’s usually half the distance, so four inches, usually, is where they start to smell it instead of eight inches.”

Now things have gone a step beyond this simple home test. Here’s what’s going on. . .

An Early Warning System

Recent findings by scientists at McGill University in Montreal, Canada have advanced our knowledge of how odor tests can be used as an early indicator of Alzheimer’s risk, well before you notice any memory loss.

Located high up in the nasal cavity, where odors enter, are our olfactory receptors. From here, nerve fibers lead to specialized structures called olfactory bulbs in the front part of the brain.

The nerve endings at this point receive impulses and send them to higher olfactory centers at the base of the brain with the message “this is lemon” or “this is bacon.”

These olfactory brain regions not only identify odors, but are also involved with memory and emotion. These areas are particularly vulnerable to Alzheimer’s pathology.

Doubles the Risk of Memory Loss

In a Mayo Clinic study published in JAMA Neurology in 2016, 1,430 men and women, with an average age of 79, and assessed as being in good cognitive shape, were given a smell identification test. They were followed up after 3½ years during which 250 developed mild cognitive impairment (MCI), an early sign of Alzheimer’s.

The researchers found that as the test performance got worse, so did the risk of memory loss. Dividing all the scores equally into four quarters, the researchers found seniors in the second quarter from the top had a 12% increased risk compared to the those in first quarter. This rose to 95% in the third, and more than double in the bottom quarter.

In a second part to the study, they also found that odor identification predicted the progression of mild memory loss to Alzheimer’s.

These findings were consistent with previous studies.

Odor Loss Linked with Markers for Alzheimer’s

For the McGill study, the research team recruited 274 people whose average age was 63. Each had a parent or multiple siblings with Alzheimer’s.

They were given the University of Pennsylvania Smell Identification Test which consists of four booklets containing ten “scratch and sniff” odorized strips in each.

The subjects must choose between four possible choices – listed above the strip – to decide what the odor is. The 40 smells range from banana and cinnamon to bubble gum, motor oil and root beer.

In addition, 101 of the participants donated cerebrospinal fluid (CSF) to be tested for the Alzheimer’s-related proteins tau and beta-amyloid, which are located in the lumbar region as well as the brain.

The principal finding of the study was that as participants showed less ability to identify the odors, the evidence of Alzheimer’s pathology in their spinal fluid increased.

This association survived even after adjustment for other risk factors such as age, gender, education, APOE4 status, cognitive scores and brain/olfactory health history.

Lead author Marie-Elyse Lafaille-Magnan holds a doctorate in neuroscience. She commented, “This is the first time that anyone has been able to show clearly that the loss of the ability to identify smells is correlated with biological markers indicating the advance of the disease.”

Another member of the team, Dr. John Breitner, added, “…if we can delay the onset of symptoms by just five years, we should be able to reduce the prevalence and severity of these symptoms by more than 50%.”

The Canary in the Coal Mine

Davangere Devanand, a Professor of Psychiatry and Neurology at Columbia University, believes that olfaction status is “important not just because it’s novel and interesting and simple but because the evidence is strong.”

Jayant Pinto, MD, Professor of Surgery at the University of Chicago, joined with four colleagues to go even further, calling olfaction “the canary in the coal mine of human health.”

The smell test appears to be a simple, low cost, early, and reliable warning of future Alzheimer’s.

However, if you feel you’re losing your sense of smell, please don’t be alarmed. The number one reason this occurs is due to the common cold. The loss can last for months afterwards or even become permanent. Other causes are sinus infections, hay fever and nasal polyps.