Here's what we know from a study of senior citizens sniffing scented markers for science: Your sense of smell is as good an indicator of your five-year risk of death as heart failure, lung disease, and cancer, and perhaps a better one.
A good sense of smell isn't the usual thing doctors look for when predicting how long a patient has to live. That's a role usually reserved for factors like mental state, disease, and mobility. After all, a patient with dementia, congestive heart failure, and difficulty getting out of bed probably isn't going to live a whole lot longer. On the other hand, a decline in the ability to detect different smells often precedes neurodegenerative diseases such as Parkinson's and Alzheimer's, one of the leading causes of death in the United States. And that, Jayant Pinto and colleagues at the University of Chicago observed, might mean they could assess the risk not just of neurological disease but also mortality risk based on simple tests of smell.
"We believe olfaction is the canary in the coal mine of human health, not that its decline directly causes death."
To find out, Pinto and team included as part of the National Social Life, Health, and Aging Project a test that your stoner friends from high school might have enjoyed. In the first wave of the project, conducted in 2005 and 2006, NSHAP staff conducted in-person interviews with 3,005 men and women between the ages of 57 and 85. As part of that interview, interviewees sniffed five Burghart Sniffin' Sticks imbued with the perfumes of rose, leather, orange, peppermint, and fish and then tried to identify each aroma from a multiple-choice list. The second wave of the project, conducted five years later, was less colorful—researchers checked with interviewees, their families, news reports, and public records to see whether smell-test participants were still alive.
As the researchers suspected, they found that smell was a solid predictor of mortality. Only about 10 percent of those who scored 100 percent on the test died within the following five years, while a third of those who couldn't correctly identify a single smell died. That held up even after controlling for age, gender, race, education, and even serious medical conditions like heart disease, cancer, liver failure, or stroke. After taking all those into account, an inability to identify common odors indicated older adults were nearly two and half times more likely to die within five years than those who could smell just fine.
Still, the researchers aren't saying that people will die of a failing nose. "We believe olfaction is the canary in the coal mine of human health, not that its decline directly causes death. Olfactory dysfunction is a harbinger of either fundamental mechanisms of aging, environmental exposure [to pollution, toxins, or pathogens], or interactions between the two," the authors write in PLoS One.