For many, the idea of developing Alzheimer’s disease brings to mind the loss of memories and overall cognitive decline over time. And while this symptom can make itself hard to diagnose early, scientists are beginning to better understand that there are other signs the onset of the disease has begun. In fact, one study has found that not being able to smell certain scents could be a sign that someone is at high risk of Alzheimer’s disease. Read on to see which aromas could soon be used as a test for the neurological condition.
A 2017 study carried out by researchers at McGill University used 274 participants with a mean age of 63 and who had been identified as being genetically at-risk for Alzheimer’s. The subjects were then given scratch-and-sniff cards with very distinguishable and various scents, including bubble gum, lemon, and gasoline, and asked to identify them.
One hundred patients also agreed to regular lumbar punctures so researchers could measure the levels of certain proteins in their cerebrospinal fluid (CSF) that are linked to Alzheimer’s disease. The tests found that the participants who had the hardest time identifying the smells also had the most proteins indicating a high Alzheimer’s risk in their CSF.
The study’s results, which were published in the journal Neurology, add weight to a popular theory that Alzheimer’s can affect the area of the brain responsible for taste and smell known as the olfactory bulb. The researchers behind the study say it could help link anosmia—or the medical term for the loss of smell—with the onset of Alzheimer’s.
“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,” Marie-Elyse Lafaille-Magnan, the study’s lead author, said in a news release.
“For more than 30 years, scientists have been exploring the connection between memory loss and the difficulty that patients may have in identifying different odors. This makes sense because it’s known that the olfactory bulb (involved with the sense of smell) and the entorhinal cortex (involved with memory and naming of odors) are among the first brain structures first to be affected by the disease.”
The study’s authors pointed out that the results pointed towards Alzheimer’s being much easier to spot early on and diagnose in the future. “This means that a simple smell test may potentially be able to give us information about the progression of the disease that is similar to the much more invasive and expensive tests of the cerebrospinal fluid that are currently being used,” John Breitner, MD, the director of the Centre for Studies on Prevention of Alzheimer’s Disease at McGill University and the study’s co-author, said in a statement.
“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 percent.” But, he still cautioned: “Problems identifying smells may be indicative of other medical conditions apart from [Alzheimer’s disease] and so should not be substituted for the current tests.”
This isn’t the first research to find a connection between the sense of smell and cognitive decline. For example, a 2017 study published in the Journal of the American Geriatrics Society determined that a strong link exists between olfactory decline and dementia. The study’s researchers assembled a “nationally representative sample” of 2,906 men and women between the ages of 57 and 85, who completed a short interview and underwent a five-item smell test. Subjects were tasked with identifying five scents—peppermint, fish, orange, rose, and leather—by sniffing “a device similar to a felt-tip pen.” They were then provided four possible answers and asked to identify which one they were smelling.
Five years later, the research team conducted a follow-up interview. They found that those who were unable to identify at least four out of the five odors were more than twice as likely to have developed dementia during that time.
“These results show that the sense of smell is closely connected with brain function and health,” said Jayant M. Pinto, MD, a professor of surgery at the University of Chicago in Illinois and senior author of the study. “We think a decline in the ability to smell, specifically, but also sensory function more broadly, may be an important early sign, marking people at greater risk for dementia,” he told Medical News Today.