The nose knows when time is short. (Photography by Chrispl57, CC BY-NC-ND 2.0)

A sense of mortality

Underappreciated—but, it turns out, important—the olfactory system issues an SOS.

Think your sense of smell isn’t as sharp as it used to be? Go see your doctor—now. Turns out, olfaction’s repertoire is even more sweeping than previously realized. Not only does smell heighten mother-baby bonding, fuel nutrition, safeguard against toxins, enhance pleasure, and trigger memories long forgotten. It also predicts death among older adults.

“You have more than three times higher odds of death in the next five years if you have no sense of smell compared to those with a normal sense of smell,” says UChicago surgeon Jayant Pinto, a specialist in sinus and nasal diseases. His data analysis on adults aged 57 to 85, published this past fall in PLOS ONE, sheds new light on one of the less appreciated of the five main senses.

“It’s not in the public consciousness,” says Pinto, who studies risk factors for diseases of the nose among the aging. “People think, ‘I’m getting older. I’m going to get a hearing test’ or ‘I’m going to get a vision test,’” he says. “They don’t think, ‘My smell is declining.’”

They should. Many Alzheimer’s patients experience a weakening sense of smell as their first symptom. It frequently occurs in early-stage Parkinson’s disease as well. Such facts seemed to suggest that olfaction has important implications for brain health, but its relationship to mortality wasn’t clear. Pinto wondered: could diminished sense of smell predict death?

“We wanted to answer this question definitively,” he says. To do so, he needed to track people over time. Enter the National Social Life, Health, and Aging Project, the first-ever nationally representative study of social relationships and health among older Americans. Led by NORC at the University of Chicago, the longitudinal initiative sent research teams into more than 3,000 homes to gather data on topics as diverse as cognitive function, sexuality, financial resources, quality of relationships, and physical health.

Their collection included information on sense of smell. Subjects were asked to sniff a scented felt-tipped pen and identify five common odors—rose, leather, orange, fish, and peppermint—from among four choices. Nearly 78 percent of individuals had normal smell function, correctly identifying four or five of the scents, and another 20 percent were able to identify three of the five. But 3.5 percent could name only one scent or none. They were labeled “anosmic.”

The first wave of surveys was conducted in 2005 and 2006. When researchers followed up five years later, in 2010 and 2011, 430 of the study’s original subjects had died. The most likely to be deceased were those people who had demonstrated the most impaired sense of smell, the 3.5 percent group.

“We were surprised,” says Pinto, who initially thought that an age effect could be at work. After all, it made sense that the oldest people would have died and, because smell often declines with age, that could be a confounding variable. He and his team reanalyzed the data, controlling for a host of factors including age, gender, socioeconomic status, physical health, and cognitive function.

The relationship between declining smell and approaching death remained unchanged. In fact, not only was impaired smell a risk factor for death in the next five years, it was a stronger predictor of mortality than heart failure, lung disease, and cancer.

The question was why.

“We don’t think that you lose your sense of smell and that kills you directly,” Pinto clarifies. Instead, olfactory dysfunction seems to act as a biomarker, tipping us off that something is amiss. It’s the “canary in the coal mine of human health.”

He’s currently researching how that signaling works, homing in on two key hypotheses. The first is that smell loss is a harbinger of physiological shutdown. Unlike the other senses, the olfactory system relies on a continuous regeneration of stem cells. A weakening sense of smell could indicate a more global decline in the body’s ability to generate new cells and repair itself.

Secondly, it might be a marker of environmental exposure. Housed in the roof of the nasal cavity, the olfactory nerve is the only cranial nerve directly exposed to the outside environment. “Over time, as that nerve gets beaten down by exposures,” Pinto says, diminished olfactory function “could be a sign your body is also getting beaten down.” Attackers could include pollutants, toxins, and even microbes that slowly wear away at the nerve—and the rest of the body.

As Pinto and his team investigate the why behind their findings, he urges doctors to take smell loss seriously. “This paper is a warning call,” he says. “If your patient has a deteriorating sense of smell, it’s a sign they need more attention. Find out what’s going on—and see if you can intervene to prevent any untoward health effects.”