The nose knows

Failure to recognise smells could be an indicator as to how long a person may live.

Death is inevitable. No matter how many times we tell ourselves that death is part and parcel of life, we are never prepared for it. It is for this reason some of us would like to be able to foretell deaths. There is a simple test for that!

Bear in mind that the test may not be as accurate as expected, and getting people to participate in it may be a little tough. It is based on the nose’s ability to detect odours. The test deals with probabilities, and it will not tell you exactly when a person is going to die.

You may give a willing participant five odours to identify - rose, fish, mint, leather and orange. If the person being tested gets four or all odours wrong, then that’s something to look into.

There are many diseases where the sense of smell decreases with the progression of the disease - Parkinson’s and dementia for example. This discoveries led to the speculation that perhaps there are many other diseases which could result in the loss of the sense of smell and to turn the idea around,  perhaps the sense of smell could be used to predict deaths.

This theory was tested by a group in 2001 using a group of elderly people (described in a paper published in 2011 by Wilson et al). The group of over a thousand people was given a rather complicated smell-identification test involving twelve odours and a choice of four answers, one of which was correct.  The group was followed through the years and after four years, about a third of them died. Analyses of the smell-identification results for the group that had died with a matched group (similar illnesses and severity as judged by other tests) from the surviving cohort showed that the group that had died  had done much worse on the smell-test on average. In fact, it appeared that each wrong smell-identification had increased the risk of death 6% over the background risk.

A similar but simpler paper was published in 2014 and caught the eye of many. It involved a five smell test (using the odours mentioned at the start) with a larger group of about 3000 people. The age group was broader this time (57-85) and again, the participants were asked the correctly identify the  five odours, given a choice of possible responses. Five years later, the participants were tracked down and two groups were compared, those that had died and those that survived. A striking difference in the smell-test was once again noted. There was a three-fold greater chance of death among participants  who got none or only one of the odours correct, compared to those who got five or six.

How can the failure to recognise smells be a good predictor of mortality? One possible explanation that has been put forward is that our ability to smell relies on regular replenishment of our smell-cells by the stem cells. None of our other senses are so directly reliant. As our body loses its ability  to repair itself and gradually falls into a state of disrepair, we begin to lose both our sense of smell and the war to survive. The explanation seems plausible and certainly the simplicity of the test and the clarity of the results are striking. As for the test mentioned at the start, it may be difficult  to get people to participate in it. But why not give it a try yourself?

The School of Science, Monash Malaysia gives you the opportunity to learn more about the subjects discussed above. Contact the School if you are interested.


Sadequr Rahman is Professor of Plant Genetics at the School of Science, Monash University Malaysia. Prior to joining Monash in 2011, he worked and studied at leading research institutes and universities in Australia, Japan, Bangladesh, Canada and the UK. His particular interests are in the application    of molecular genetics and genomics for increased rice productivity and biodiversity studies. He also has long standing interests in making science accessible to the layman and in the encouragement of evidence-based thinking. He regularly produces and presents broadcasts on science-related and more general    topics for a community radio station in Australia.

The article was first published in The Petri Dish, the monthly newspaper of Malaysian Biotechnology Information Centre (MABIC).