By Dennis Thompson
MONDAY, April 29, 2019 (HealthDay News) -- They say the nose knows, but can a loss of smell signal impending death?
Possibly, researchers say.
They discovered that a poor sense of smell was associated with a nearly 50% higher risk of death within the next decade for adults older than 70.
While the study didn't prove cause and effect, that association is enough to make some experts wonder whether seniors' sense of smell should be tested alongside their other vital signs.
"I would not be surprised if someday the sense of smell was included as a simple checkup, to see if this important human sense is affected," said senior researcher Dr. Honglei Chen, a professor of epidemiology and biostatistics at Michigan State University.
As many as 1 in 4 aging Americans suffers a loss in their sense of smell, researchers said in background notes.
Further, research has linked the loss of an ability to smell to your risk of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and some dementias, Chen said.
But Chen and his colleagues suspected that sense of smell might have broader health implications for seniors than just a predisposition to brain conditions.
So they analyzed data from nearly 2,300 adults between the ages of 71 and 82 who were tracked as part of a larger health study.
Participants took a brief smell identification test as part of a battery of health examinations. They then were tracked for about 17 years, to see what illnesses might affect them.
It's unusual for seniors to have their sense of smell tested, said Vidyulata Kamath, an assistant professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine in Baltimore.
"We notice when our vision is changing. There's some evidence when our hearing is changing. But what studies have shown is there is a sizable discrepancy between people's report of their sense of smell functioning versus their actual scores on objective testing," Kamath said. "There's a sizable number of adults who have an unawareness of olfactory [sense of smell] loss."
Kamath wrote an editorial accompanying the study. Both are published April 30 in Annals of Internal Medicine.
Even worse, the new study showed that a loss of smell did indeed serve as a warning that death could be approaching.
"We found that compared to people with a good sense of smell, those with a poor sense of smell had about a 48% higher risk for death at year 10 and a 30% higher risk at year 13," Chen said. "As we are talking about an older population, this risk is not small at all."
The association was largely limited to people who reported themselves in good or excellent health at the start of the study, Chen noted.
"This suggested to us it's an early and probably sensitive marker for ongoing health conditions that may not be regularly recognized by the participants themselves," Chen said.
What's more, the researchers found that the conditions already linked to poor sense of smell only accounted for about 28% of the higher death risk. That includes 22% of the risk attributable to neurodegenerative diseases, and 6% linked to weight loss, researchers reported.
"When you lose your sense of smell, that can have downstream effects on your appetite," explained Kamath. "You may not be able to enjoy food the way you did before. You might have reduced food intake. That can potentially lead to changes in body weight and changes in your nutritional status."
But that leaves unexplained more than 70% of the higher mortality associated with poor sense of smell, Chen said.
There are some theories why poor sense of smell might be tied to these deaths, but no real answers, Chen and Kamath said.
People might die in a fire because they can't smell the smoke, or die from food poisoning because they can't smell that their meal is off, but "those events are fairly rare to begin with in the general population," Chen said.
People who eat poorly due to their lost sense of smell might also be at higher risk of developing heart disease, due to malnutrition or by eating unhealthy junk foods that have a vivid taste, Chen added. Or they might have been exposed to some toxic environmental pollution that harmed their ability to smell as well as causing other damage to their bodies.
While these findings are interesting, it's still too soon to make smell exams part of seniors' regular checkups, Chen and Kamath agreed.
"I don't think we've done the study yet to show it improves clinical practice," Kamath said.
Part of that research will involve figuring out what's behind the unexplained 70% of deaths, Chen said.
"We need to know what those health consequences are before we can make recommendations," he said.