[Editor's note: we received two separate reports on this story and wanted to give attribution to both submitters. They are presented here in the order received.]
Failing a smelling test is a strong predictor of death within 5 years, according to a new study (full text).
Thirty-nine percent of study subjects who failed a simple smelling test died during that period, compared to 19 percent of those with moderate smell loss and just 10 percent of those with a healthy sense of smell.
The hazards of smell loss were "strikingly robust," the researchers note, above and beyond most chronic diseases. Olfactory dysfunction was better at predicting mortality than a diagnosis of heart failure, cancer or lung disease. Only severe liver damage was a more powerful predictor of death. For those already at high risk, lacking a sense of smell more than doubled the probability of death.
"We think loss of the sense of smell is like the canary in the coal mine," said the study's lead author Jayant M. Pinto, MD, an associate professor of surgery at the University of Chicago who specializes in the genetics and treatment of olfactory and sinus disease. "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."
Hugh Pickens writes:
Mo Costandi writes at The Guardian that a new study shows that losing one’s sense of smell strongly predicts death within five years, suggesting that the nose knows when death is imminent, and that smell may serve as a bellwether for the overall state of the body, or as a marker for exposure to environmental toxins. “Olfactory dysfunction was an independent risk factor for death, stronger than several common causes of death, such as heart failure, lung disease and cancer,” the researchers concluded, “indicating that this evolutionarily ancient special sense may signal a key mechanism that affects human longevity.” Jayant Pinto of the University of Chicago prepared special felt-tipped pens scented with five common odors—fish, leather, orange, peppermint and rose—and presented them one by one to volunteers. After each presentation, the volunteer was shown pictures and names of four possible answers, and was asked to select the correct one. Getting one answer wrong was considered okay, or “normosmic”, but two or three errors labelled a person as “hyposmic”, or smell-deficient, and four or five counted them as “anosmic”, or unable to smell. Five years later, the researchers tracked down as many of the same participants as they could, and asked them to perform this smell test a second time. During the five-year gap between the two tests, 430 of the original participants (or 12.5% of the total number) had died. Of these, 39% who had failed the first smell test died before the second test, compared to 19% of those who had moderate smell loss on the first test, and just 10% of those with a healthy sense of smell. Despite taking issues such as age, nutrition, smoking habits, poverty and overall health into account, researchers found those with the poorest sense of smell were still at greatest risk.
The researchers stress that it is unlikely to be a cause of death itself, arguing only that it is a harbinger for what is to come. The tip of the olfactory nerve, which contains the smell receptors, is the only part of the human nervous system that is continuously regenerated by stem cells. The production of new smell cells declines with age, and this is associated with a gradual reduction in our ability to detect and discriminate odours. Loss of smell may indicate that the body is entering a state of disrepair, and is no longer capable of repairing itself.
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