Poor sense of smell linked to increased mortality rate

A person’s nose knows when he or she is knocking on death’s door, according to research released Thursday showing that a severe loss of one’s sense of smell is a stronger indicator of impending death than a diagnosis of heart failure or cancer.

In a study of more than 3,000 adults the ages 57 to 85, researchers from the University of Chicago administered a test measuring how well participants could identify five common odors: peppermint, fish, orange, rose and leather. Then they followed up with all the participants five years later.

A whopping 39 percent of the people who could identify only one of the five scents died within five years, compared with just 19 percent of people who recognized two or three of the five smells, meaning that they had moderate loss of smell. Among the people who could correctly identify all five scents, just 10 percent died within five years.

The researchers statistically adjusted their results for age, gender, race, socioeconomic status, mental health and overall health, including whether participants had ever been diagnosed with a disease or whether they smoked or drank. Despite the adjustments, a strong loss of sense of smell still translated into “strikingly increased odds of death” within five years, the study said.

Smell was a stronger indicator than a diagnosis of heart disease, cancer or lung disease. Only severe liver damage had a stronger link to imminent death.

“We think loss of the sense of smell is like the canary in the coal mine,” Dr. Jayant M. Pinto, an associate professor of surgery at the University of Chicago, said in a press release. “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. Our findings could provide a useful clinical test, a quick and inexpensive way to identify patients most at risk.”

The study, published Wednesday in the journal PLOS One, is part of the university’s National Social Life, Health and Aging Project, which aims to examine the health and well-being of older adults.

The researchers didn’t look into the relationship between the olfactory system and mortality, but they have a few ideas. First, the olfactory nerve, with its receptors in the nasal passages, is the only cranial nerve exposed to the environment.

That means the central nervous system, in receiving information about scents from the olfactory nerve, may be damaged by continuous exposure to airborne toxins and pollution, which has been shown to increase the risk of dying from chronic obstructive pulmonary disease.

Also, the olfactory system is unique, the researchers wrote, in that it continuously regenerates itself with stem cells. So another reason for a marked decrease in the ability to smell could be age-related decline in the body’s overall ability to rebuild itself.

“This evolutionarily ancient special sense may signal a key mechanism that affects human longevity,” the authors wrote.