Not Smelling Death

April 3, 2015

By Medical Discovery News

This may be Debbie Downer question, but can you guess what condition is most indicative of a person’s imminent demise? It turns out that the strongest predictor of impending death is not cancer, stroke, heart attack, diabetes, or emphysema, but a person’s declining sense of smell.

Scientists at the University of Chicago have revealed that the loss of the sense of smell, officially called olfactory dysfunction, is a significant forecaster of death in older Americans. In this study, 3,005 people aged 57-85 were asked to identify five common scents: peppermint, fish, rose, leather, and orange. Five years later, the health of the same people was evaluated.

As this was an older population, some of the subjects died before the study contacted them again. The surprise was that almost 40 percent of those who died had failed the scent test, identifying only one or none correctly. Anosmia is the technical term for complete loss of the ability to smell, while hyponosmia is the significant (but not total) loss of smell. The mortality rate for those with anosmia was four times higher than for those with normal smell. Those who were hyponosmic had an intermediate mortality compared to normal individuals. So being either anosmic or hyponosmic is associated with an increase in a person’s  mortality. And because of the limited length of this study and the relatively small group examined, the effect on mortality is probably underestimated.

Overall, these results are striking. Since these were older individuals, the possibility of other factors influencing these results was examined. The study ruled out confounding factors such as nutrition, mental health, smoking, alcohol abuse, frailty, and neurodegenerative diseases in the results. Those at a higher risk for anosmia or olfactory loss were males, those who were overweight or obese, and those with a lower socioeconomic status.

While the human sense of smell is not as dominant as in other mammals (such as dogs), it is associated with good health and nutrition. The sense of smell is strongly tied to an array of brain functions and is the strongest sense tied to individual memory. Remembered scents can provoke intense memory responses and can stimulate memories from long ago.

The sense of smell is also highly connected to other parts of the central nervous system. Unique among the senses, normal olfactory function relies on cellular regeneration of the specialized sensory cells lining the inside of the nose. If the olfactory system is not working properly, these cells won’t regenerate like they are supposed to do.

Recently, we reported on a study that determined that human noses are capable of distinguishing between at least a trillion different scents. It now appears that the loss of this ability is an omen of death. The exciting part is that a simple scent test taking less than five minutes could become a powerful new way to identify those at high risk of upcoming mortality and lead to interventions that could prolong people’s lives.

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