People born without a sense of smell breathe differently to those with one, researchers have found, which could help explain why problems with odour 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 slight service” to humans – studies have associated its loss with depression, feelings of personal isolation and even an increased risk of early death.
“There’s this notion that this sense is completely unimportant, and yet if you lose it then a lot of bad things happen. So it seems 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 as loss has gained added attention as it is a common symptom of Covid. Now Sobel and colleagues say they have shed light fresh light on the conundrum.
Writing in the journal Nature Communications, the team report how they studied 21 people with congenital anosmia – meaning they have been unable to smell from birth – and 31 people who reported an unimpaired sense of smell. Each participant spent 24 hours going about their normal life while wearing a device that fitted into their nostrils and measured their airflow.
The data revealed that participants with a working sense of smell made more sniffs as they breathed in than those with anosmia, something the team suggest may be a response to smells in the environment. The idea was supported by a further experiment that revealed these extra sniffs did not occur among people with a working sense of smell when in an odour-free environment.
The researchers found that when awake, participants with anosmia had more pauses while breathing and a lower peak flow while breathing out than those without the condition, as well as other differences in their patterns of respiration while asleep – a period, the team note, when surrounding odours 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 take into account mouth breathing, and cannot prove that differences in respiration patterns drive health problems in people with anosmia. What’s more, the team included only people born without the sense of smell, although it is now carrying out work with people who lost it later in life.
While the team stressed there were other potential reasons for the association between anosmia and health problems, they say differences in breathing patterns could be a contributing factor, potentially affecting physical and mental health, including through changes in brain activity.
Sobel said the idea had precedence. “If you don’t sigh, you die,” he said. “So the notion that patterns of respiration can be really influential is not all that far-fetched.”
