In the study, 3,005 adults aged 57 through 85 were surveyed and put through an odor identification test. Most of the participants were found to have a normal sense of smell, with 20 percent showing a moderately reduced sense of smell (they got two or three out of five scents right) and 3.5 percent only identifying one scent or less. Unsurprisingly, sense of smell declined with age.

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Five years later, the researchers found that 430 of the original participants had died. Even when they adjusted their analysis to control for age, gender, socioeconomic status, race, and overall health, they found that those with mild to severe smell loss had been more likely to die. Those with severe loss of smell were four times more likely to have died than the superior sniffers.

Olfaction "is a really important brain function," said lead study author Jayant Pinto, associate professor at University of Chicago. While losing that sense has already been associated with diseases such as Alzheimer's and Parkinson's, Pinto and his colleagues found it to be a stronger predictor of mortality for older adults than heart failure or a cancer diagnosis.

It's true that there are some instances where a weakened sense of smell could actually contribute to risk of death. A decreased sense of smell leads to loss of appetite, which could be dangerous in someone whose health is on the decline. A poor sense of smell also leaves the elderly vulnerable to gas leaks and other accidents.

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But because this study didn't track down the exact cause of death of each individual, the researchers can't make these kind of connections. And it's more likely that the subjects' sense of smell was just an indicator of declining health.

"We don't believe it's a causal question here. We believe this is an indication that whatever is causing olfaction decline is causing overall health to decline," Pinto said. The olfactory system has self-regenerating stem cells, he said, so its decline may indicate a larger failure of the body to repair itself.

Scent tests could prove to be a quick and cheap way of keeping tabs on overall health in the elderly. But even people in their prime should take note of their noses.