A simple, validated “sniff” test can help to predict the likelihood that an individual will develop dementia within the next 5 years, irrespective of other risk factors, according to the results of a long-term study by researchers at the University of Chicago. The study, involving nearly 3000 adults aged 57 to 85 years, found participants who couldn’t identify at least four out of five common odors were more than twice as likely as to develop dementia within the next five years as participants who could identify all five scents.
“Loss of the sense of smell is a strong signal that something has gone wrong and significant damage has been done,” commented Jayant M. Pinto, M.D., professor of surgery at the University of Chicago. “This simple smell test could provide a quick and inexpensive way to identify those who are already at high risk.”
Dr. Pinto and colleagues published their findings this week in the Journal of the American Geriatrics Society, in a paper entitled “Olfactory Dysfunction Predicts Subsequent Dementia in Older U.S. Adults.”
The new study builds on the team’s previous work, published in 2014, which indicated a link between olfactory dysfunction and an increased risk of death within 5 years. Both the prior study and this new work used devices known as “SniffinSticks” to test a participant’s ability to identify scents. SniffinSticks look like felt-tipped pens, but rather than carrying ink, they are infused with specific scents.
For the latest research, study participants tried to identify at least four out of five specific odors: peppermint, fish, orange, rose, and leather. Out of the 2906 people tested, 78.1% had a normal sense of smell, with 48.7% correctly identifying 5/5 odors, and 29.4% correctly naming 4/5. Of the total study population another 18.7% of subjects were classified as “hyposmic,” and could only name two or three of the five scents. The remaining 3.2% of people were considered “anosmic,” with 2.2% of participants identifying just one of the five scents, and 1% unable to name any of the five SniffStick smells.
Move forward five years, and all of the study subjects who hadn’t been able to name a single scent had been diagnosed with dementia, as had nearly 80% of participants who had correctly identified only one or two of the SniffStick odors. There was also a dose-dependent relationship between the degree of smell loss and the incidence of dementia. “We need to understand the underlying mechanisms,” Pinto commented, “so we can understand neurodegenerative disease and hopefully develop new treatments and preventative interventions.” Dr. Pinto is an ENT specialist and a member of the Section of Otolaryngology-Head and Neck Surgery at UChicago Medicine.
Declining sense of smell can be an early sign of Parkinson’s disease or Alzheimer’s disease, and these olfactory problems worsen as the diseases progress. The olfactory nerve is the only cranial nerve that is exposed directly to the environment, and smell-sensing cells connect with the base of the brain, which exposes the central nervous system to potential environmental hazards.
“This evolutionarily ancient special sense may signal a key mechanism that also underlies human cognition,” states co-researcher Martha K. McClintock, Ph.D., the David Lee Shillinglaw Distinguished Service Professor of Psychology at the University of Chicago. “ … a decrease in the ability to smell may signal a decrease in the brain's ability to rebuild key components that are declining with age, leading to the pathological changes of many different dementias.”
Dr. Pinto suggests that smell is the most “undervalued and underappreciated” of the human senses, “until its gone.” In fact, smells influence both nutrition and mental health, he adds. People who lack a sense of smell can't tell when food has gone off, or when there’s a fire, for example. “Being unable to smell is closely associated with depression as people don't get as much pleasure in life.”
The authors acknowledge that more work will be needed before an olfactory test could be developed for clinical use. “Our test simply marks someone for closer attention,” Pinto concluded. “But it could help find people who are at risk. Then we could enroll them in early-stage prevention trials.”