If you want to know how long you'll live, your nose might help you sniff out the answer, a new study suggests.
In a study of older adults, researchers have found a link between the inability to identify certain scents— like peppermint or fish — and an increased risk of mortality over the next five years. Known as "olfactory dysfunction," the loss of smell is an even stronger predictor of when a person will likely die than conditions such as heart failure, cancer or lung disease, according to researchers at the University of Chicago.
"We think loss of the sense of smell is like the canary in the coal mine," lead author Dr. Jayant Pinto, an associate professor of surgery at the University of Chicago, said in a statement. "It doesn't directly cause death, but it's a harbinger — an early warning that something has gone badly wrong, that damage has been done."
For the study, researchers administered a simple smell test to 3,005 participants ages 57 to 85. Each participant was asked to identify five common smells: peppermint, fish, orange, rose and leather. The majority of participants (nearly 78 percent) were found to have normal smelling abilities, meaning they correctly identified at least four of the five smells. Nearly twenty percent correctly identified two or three of the five scents, and the remaining 3.5 percent of participants could identify none or only one of the five scents.
Five years after this initial smell test, the researchers confirmed which of the study participants were still alive. They found that 430 of the original smellers (12.5 percent) had passed away, including 39 percent of those who had shown significant loss of smelling power five years earlier (i.e., they had identified none or only one of the test scents). Nineteen percent of the participants who had exhibited moderate smell loss five years prior were among those who died. However, just 10 percent of those who aced their smell tests died within the five-year period, the study found.
"Obviously, people don't die just because their olfactory system is damaged," Martha McClintock, co-author of the study and a professor of psychology at the University of Chicago, said in a statement. However, a decreased ability to smell may signal what McClintock called a "decrease in the body's ability to rebuild key components that are declining with age," leading to death by other causes.
Olfactory dysfunction, as McClintock noted, could be a sign of slowed cellular regeneration. Or, it could be the result of years of toxic environmental exposures, the researchers said.
In the paper outlining their study, the researchers noted the role of olfaction (the ability to smell) as an ancestral chemical system that's linked to many physiological processes. For example, smell helps humans maintain proper nutrition, aiding appetite and preference for certain kinds of food. The ability to smell is also linked to the detection of environmental hazards and pathogens and is even associated with emotions and memory, the researchers pointed out.
Other studies on ways to predict mortality have focused more on physical indications that health might be failing. One study, conducted in 2011 by researchers at the University of Pittsburgh, found that people who walk 1 meter per second (about 2.25 mph) or faster consistently live longer than others of their age and sex who walk more slowly.
And a 2010 study based on a review of 28 smaller studies found that people who perform badly on simple physical tests — including those related to gripping, walking, rising from a chair and balancing on one leg — are at an increased risk of death compared with those who perform well on such tests.
But using smell to predict mortality might be easier than conducting tests for physical capabilities, Pinto said. The smell test conducted for the study used "Sniffin' Sticks," odor-dispensing devices that look like felt-tip pens and are loaded with aromas rather than ink.
"Our findings could provide a useful clinical test — a quick and inexpensive way to identify patients most at risk," Pinto said.
The study was published today (Oct. 1) in the journal PLOS ONE.