While the finding may seem odd, a poor sense of smell raises the odds of death more than established medical conditions including cancer.The U.S. researchers said that while the dulling of the sense does not directly cause death, it provides ‘early warning that something has gone badly wrong’.
They believe that a simple smell test could be used to identify pensioners most at risk of an early death.
University of Chicago researcher Jayant Pinto said: ‘Of all the human senses, smell is the most undervalued and underappreciated – until it’s gone.’
But British experts urged people not to panic – and said that much more research is needed to confirm the link.
In the first study of its kind, more than 3,000 men and women aged between 57 and 85 were put through a three-minute smell test.
They were asked to sniff the scent given off by felt tip-pen like gadgets and given four possible answers.
They did this five times. The fragrances used were, in order of increasing difficulty, peppermint, fish, orange, rose and leather.
Most of the men and women got at least four of the five right, meaning they had a normal sense of smell.
Almost 20 per cent only identified two or three of the smells – indicating a mild loss of the sense.
Some 3.5 per cent got one or none right – and were judged to be ‘anosmic’ – or to have lost their sense of smell.
Five years later, 430 of the men and women had died.
Those who had failed the smell test were almost six times as likely to have died as those with a healthy sense of smell, the journal PLOS ONE reports.
The finding could be partly explained by age, gender and socio-economic status. But, even when these were taken into account, someone without a sense of smell was more than three times as likely to have died.
Even a moderate loss of sense of smell raised the odds of an early death.
What is more the link wasn’t simply due to those with poor sense of smell having lost their appetite, or drinking or smoking more, having cancer or heart problems or being generally frail.
In fact, not being able to smell things provides a more accurate warning of an early death than cancer or heart failure.
Only severe liver damage is more strongly linked to dying within five years.
Dr Pinto said: ‘We think that loss of sense of smell is like the canary in the coal mine.
‘It doesn’t directly cause death, but it’s a harbinger, an early warning that something has gone badly wrong.’
One possibility is that the health of the olfactory nerve, which carries information on smell from the nose to the brain, is a sign of overall health.
If it has become old, worn and unable to repair itself, the brain and body may be in the same position.
Another possible explanation is that infections, poisons and pollutants that we breathe in damage our sense of smell before harming the brain and body.
Dr Pinto said: ‘Pollution can affect heart, lung and brain disease, predisposing to early death.’
Dr Martha McClintock, the study’s senior author, said: ‘This evolutionary ancient special sense may signal a key mechanism that affects human longevity.’
Nirmal Kumar, a consultant head and neck surgeon, described the research as interesting – but questioned the reliability of the smell test used.
He would give a patient 40 different fragrances, rather than just five, to establish if they have lost their ability to identify smells.
Professor Kumar, honorary secretary of ENT UK, the British association for ear, nose and throat specialists, added that people who are starting to lose their sense of smell shouldn’t panic.
However, they should seek medical help as previous studies have linked the loss with the early stage of Alzheimer’s and Parkinson’s diseases.
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