Being unable to smell bacon frying may be far more dire than simply missing out on one of life's pleasures. In older adults, it could be a predictor of increased risk of death within five years.
In a study of more than 3,000 people aged 57 to 85, 39 percent of subjects who failed a simple smelling test died within five years, according to results published on Wednesday in the science journal PLOS ONE.
That compared with a 19 percent death rate within five years for those with moderate smell loss and 10 percent for those deemed to have a healthy sense of smell.
"Compared to a person with a normal sense of smell, a person with an absent sense of smell has three times greater risk of dying within a five-year span," Dr. Jayant Pinto, the study's lead author, said in a telephone interview.
"What this tells us is your sense of smell is a great indicator of your overall health," said Pinto, an associate professor at the University of Chicago who specializes in genetics and treatment of olfactory and sinus disease.
He likened the loss of smell to a canary in a coal mine. "It doesn't cause death, but it's an early warning that something has gone badly wrong."
The smell test was conducted in 2005 using "Sniffin' Sticks," which resemble felt-tip pens, that were loaded with five different odors subjects were asked to identify: peppermint, fish, orange, rose or leather.
Nearly 78 percent of those tested were able to identify at least four of the five scents and so classified as having normal sense of smell. Almost 20 percent got two or three of the scents right, while the remaining 3.5 percent could correctly identify one or none of the five, researchers said.
In 2010 and 2011, the survey team confirmed which participants were still alive. During the five years, 430 of the 3,005 subjects, or 12.5 percent, had died.
Researchers conducted interviews to adjust for variables and risk factors, such as age, smoking, alcohol use, overall health and socioeconomic status. In the end, those with greater smell loss when first tested were substantially more likely to have died five years later.
"It predicted it quite strongly," Pinto said.
Researchers noted that a healthy olfactory system has stem cells that self-regenerate. They speculated that a loss of smell could signal a decrease in the body's ability to rebuild key components and may be a harbinger of more serious health problems.
"If one's sense of smell is in decline, it's a warning sign for doctors taking care of such patients," Pinto said.