A declining sense of smell in older people is a strong predictor of death, according to research.
Thirty-nine per cent of study subjects who failed a simple smelling test died within five years, compared with 19 per cent of those with moderate smell loss and just 10 per cent of those with a healthy sense of smell, the journal PLOS ONE reported.
"We think loss of the sense of smell is like the canary in the coal mine," said the study's lead author Jayant Pinto, an associate professor of surgery at the University of Chicago.
"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."
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Researchers said 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, they said.
Precisely how sense of smell loss relates to mortality is unclear.
"Obviously, people don't die just because their olfactory system is damaged," said Martha McClintock.
Pinto added: "Of all human senses, smell is the most undervalued and underappreciated - until it's gone."
The US study published on Wednesday used a well-validated test for a field survey of 3005 participants.
It measured their ability to identify five distinct common odours.
After five years 430 (12.5 per cent) of the original 3005 study subjects had died and 2565 were still alive.
