People who fail to recognize common odors could be at risk for dementia, researchers from the University of Chicago found.
Researchers looked at nearly 3,000 adults ages 57 to 85 and found people who cannot identify at least four out of five common scents are twice more likely to develop dementia within five years than those who can recognize the smells.
"Loss of the sense of smell is a strong signal that something has gone wrong and significant damage has been done," the study's lead author, Dr. Jayant M.Pinto, said in a statement. "This simple smell test could provide a quick and inexpensive way to identify those who are already at high risk."
For the study, researchers used “Sniffin’ Sticks,” which look like markers. Instead of ink, the sticks were infused with different scents. Participants were told to smell the Sniffin’ Sticks one at a time and identify the scent.
The smell participants mostly had trouble with was peppermint, followed by fish, orange, rose and leather.
Among the study’s participants, 78 percent of those tested correctly identified four of five scents. Meanwhile, 14 percent could only recognize three out of five smells, five percent identified only two scents, two percent only one scent and one percent couldn’t recognize any of the scents.
During a five-year follow-up, researchers found almost all of the participants who failed to name a single scent had been diagnosed with dementia. Among those who could only identify one or two scents, nearly 80 percent of them were diagnosed with dementia.
"These results show that the sense of smell is closely connected with brain function and health," said Pinto, an ear, nose and throat specialist. "We think smell ability specifically, but also sensory function more broadly, may be an important early sign, marking people at greater risk for dementia."
Pinto added more knowledge is needed in the underlying mechanisms so experts can understand dementia and develop new treatments for the disease, as well as prevention steps.
"Of all human senses," Pinto said, "smell is the most undervalued and underappreciated -- until it's gone."
He added that losing the sense of smell can impact a person’s lifestyle and could also risk a their safety.
“People who can't smell face everyday problems such as knowing whether food is spoiled, detecting smoke during a fire, or assessing the need a shower after a workout,” said Pinto. “Being unable to smell is closely associated with depression as people don't get as much pleasure in life."
Humans can smell through the olfactory nerve. Problems with the olfactory nerve are usually a sign of Parkinson's or Alzheimer's disease and most likely get worse as the disease advances.
The study was published in the Journal of the American Geriatrics Society.