People born without a sense of smell smell differently than those with one, researchers have found, which may help explain why problems with smell perception are associated with a host of health issues.
While some have dismissed the sense of smell as unimportant – Charles Darwin said it was “of extremely little service” to humans – studies associated its loss with depression, feelings of personal isolation and even an increased risk of early death.
“There is the idea that this sense is completely unimportant, and yet a lot of bad things happen when you lose it. So it looks like a paradox,” said Prof. Noam Sobel, a co-author of the research, from the Weizmann Institute of Science in Israel.
The impact of such loss has received additional attention as it is a common symptom of Covid. Now Sobel and colleagues say they have shed new light on the mystery.
Write in the journal Nature communicationreports the team, how they studied 21 people with congenital anosmia — meaning they were unable to smell from birth — and 31 people who reported an unimpaired sense of smell. Each participant spent 24 hours going about their normal lives while wearing a device that fit into their nostrils and measured their airflow.
The data revealed that participants with a functioning sense of smell sniffed more while inhaling than those with anosmia, something the team suggests may be a response to environmental smells. The idea was supported by a further experiment which revealed that this extra sniff did not occur among people with a working sense of smell in an odor-free environment.
The researchers found that when awake, participants with anosmia had more pauses in breathing and a lower peak flow during breathing than those without the condition, as well as other differences in their patterns of breathing while sleeping – a period, the team noted, when ambient odors remain largely constant.
The researchers fed their data into a machine learning algorithm and found that it was able to predict whether or not a participant had anosmia with an overall accuracy of 83%.
The study has limitations, including that it is small, did not specifically consider mouth breathing, and cannot prove that differences in breathing patterns cause health problems in people with anosmia. What’s more, the team only included people who were born without the sense of smell, although it is now working with people who lost it later in life.
While the team emphasized that there were other possible reasons for the link between anosmia and health problems, they say differences in breathing patterns may be a contributing factor, potentially affecting physical and mental health, including through changes in brain activity.
Sobel said the idea took precedence. “If you don’t sigh, you die,” he said. “So the idea that patterns of breathing can be really influential is not so far-fetched.”
