Loss of smell predicts death
The loss of a sense of smell can predict death within five years, according to research published today in the online journal PLOS ONE.
The study was from the National Social Life, Health and Ageing Project (NSHAP) and involved more than 3000 US participants aged between 57 and 85. It was conducted by Jayant Pinto and colleagues from the University of Chicago.
They asked the participants to identify five common odours – rose, leather, fish, orange and peppermint – as a way of assessing the accuracy and robustness of their sense of smell.
After five years, the participants were asked to take the test again. During the five year gap, 430 participants (12.5% of the total) had died, with 39% of those who failed the first smell test dying before the second test. Of those who had scored moderately well on the first test, 19% had died by the second test, while only 10% of those who had a healthy sense of smell on the original test had died during the period.
Surprisingly, loss of smell was a more accurate predictor of imminent death than a cancer diagnosis, heart disease or lung failure.
However the researchers argue smell loss does not cause death. The smell receptors, on the tip of the olfactory nerve, are continuously regenerated by stem cells, which makes them unique in the human body. One hypothesis is that the production of stem cells falls away as we age, affecting our sense of smell and indicating the body can no longer repair itself.