WEDNESDAY, Oct. 1, 2014 (HealthDay News) -- Older adults who have trouble smelling the roses -- literally -- may face an increased risk of dying in the next several years, new research suggests.
In a study of over 3,000 older Americans, researchers found those who were unable to detect scents such as rose, orange and peppermint were more than three times as likely to die in the next five years, versus those with a sharp sense of smell.
In fact, anosmia -- the inability to distinguish odors -- was a bigger predictor of death than major killers such as heart disease, lung disease or cancer, the researchers reported Oct. 1 in the online journal PLOS One.
"We were pretty surprised it was such a strong predictor," said lead researcher Dr. Jayant Pinto, a surgeon at the University of Chicago who specializes in nasal disorders.
Now, the question is why. No one is saying anosmia itself kills people, stressed Pamela Dalton, a researcher at the nonprofit Monell Chemical Senses Center in Philadelphia.
"There's no need for people to be scared," said Dalton, who wasn't involved in the study. But, she said, the findings are important, because they suggest that problems with smell detection can sometimes be a "harbinger" of health issues to come.
According to the U.S. National Institutes of Health, 1 to 2 percent of North Americans have trouble detecting scents. In some cases, Dalton said, there is a specific cause, such as benign growths in the nasal cavity, a head injury, or -- for a small number of people -- lasting effects from a respiratory infection.
But aging is the main culprit behind loss of smell, Pinto said.
Up to one-quarter of men in their 60s, and 11 percent of women, may have a "smell disorder," according to the Institutes of Health.
In Pinto's study, however, age didn't explain the link between anosmia and death risk.
Neither did other risk factors for smell loss, such as smoking and heavy drinking. The researchers also accounted for major diseases, including heart disease, stroke, cancer, diabetes and lung disease, as well as study participants' performance on a test of memory and thinking skills.
Other research has found that problems with scent detection can precede mental decline and dementia, Pinto explained. "Interestingly enough," he said, "when we controlled for [mental] decline, we still saw this association" between smell loss and death risk.
The findings are based on 3,005 U.S. adults ages 57 to 85 who were asked to identify five odors: rose, orange, peppermint, leather and fish.
Overall, 78 percent correctly named at least four, and were considered to have a normal sense of smell. Another 20 percent identified two or three scents; close to 4 percent sniffed out no more than one scent, and were considered to have anosmia.
Over the next five years, 39 percent of people with anosmia died, versus 19 percent of those with moderate smell loss, and 10 percent of those with a healthy sense of smell.
So what's going on? One theory, Pinto said, is that a poor sense of smell is associated with lifetime exposure to toxins such as on-the-job chemicals or air pollution.
Pinto explained that the olfactory nerve, which carries scent information to the brain, is the only one of the cranial nerves that is directly exposed to the environment.
He also noted that, unlike our other senses, the sense of smell depends on a constant turnover of primitive cells called stem cells.
"In theory," Pinto said, "[anosmia] could be an indicator that the body's overall regenerative capacity is in decline."
He said more research is needed to understand the reasons for the findings, and to see whether smell loss is linked to particular causes of death.
For now, Pinto said, "I hope this raises awareness that our sense of smell is important."
Problems with smell can be subtle, and people may only realize something is wrong when they can no longer taste and enjoy food, Pinto said. "If you notice a problem, tell your doctor," he advised. If the cause of the smell loss is treatable, that should improve your quality of life, Pinto said.
Dalton agreed, and said she'd like to see doctors routinely evaluate people's sense of smell, just as they check vision and hearing.
The U.S. National Institutes of Health has more on smell disorders.