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REHOVOT, Israel — A new study is challenging our understanding of how the loss of smell affects the human body. Scientists in Israel have discovered that people who do not have a sense of smell breathe completely differently than those with normal smelling abilities. This finding could help explain why the loss of smell — a condition known as anosmia — is linked to shorter lifespans and other health problems.
The research, published in the journal Nature Communications, reveals that while people born without a sense of smell breathe at the same overall rate as everyone else, their breathing patterns show marked differences in both waking and sleeping hours. Most notably, they take significantly fewer “sniffs” throughout the day — about 240 fewer per hour — compared to people with normal smell.
To conduct this research, scientists at the Weizmann Institute of Science recruited 21 people with congenital anosmia (being born without smell) and 31 people with normal smelling abilities. The participants wore a specially designed device that precisely measured their nasal airflow for 24-hour periods as they went about their daily routines. This wearable technology, which connected to their nostrils through small tubes, recorded detailed information about their breathing patterns.
The results reveal that while both groups took about the same number of breaths per minute, people with a normal sense of smell showed many more small peaks in their breathing patterns during wakeful hours. These additional peaks, which the researchers associated with unconscious “exploratory sniffing,” disappeared when people with normal smell were placed in an odorless room, suggesting these extra breaths are indeed related to people sampling their environment for smells.
Perhaps more surprisingly, the differences in breathing patterns extended into sleep — when conscious smell exploration isn’t happening. People born without a sense of smell had more fluctuations in their breathing volumes during sleep and other distinctive breathing characteristics during both sleep and wake periods. These findings suggest that growing up without a sense of smell fundamentally alters how the respiratory system functions.
The differences were so consistent that researchers could identify who had anosmia with 83% accuracy just by looking at their breathing patterns, without any smell testing at all.
This research might help explain why losing your sense of smell can have such profound effects on health and longevity. Previous studies have found that older adults who lose their sense of smell have more than three times the risk of death within five years compared to those with normal smell. While some of this increased risk might be due to the loss of smell itself — such as not being able to detect smoke or spoiled food — the researchers suggest that altered breathing patterns might play a significant role.
The findings are particularly relevant given the recent global wave of smell loss due to COVID-19, which affected millions of people. While this study focused on people born without smell, it raises important questions about how acquired smell loss might affect breathing patterns and, consequently, overall health.
Paper Summary
Methodology
The researchers used a specialized wearable device that measured airflow through each nostril separately. Participants wore this device for 24 hours while going about their normal daily activities and keeping a diary of their sleep and wake times. The device measured breathing 6 times per second, allowing it to capture subtle variations in breathing patterns that most medical devices miss. This high-precision measurement was crucial, as the researchers found that when they applied typical medical device filtering to their data, the differences between the groups disappeared completely.
Key Results
The study found four key differences in breathing patterns: 1) People with normal smell took about 24 more breaths with peaks per minute during wake periods, 2) People without smell had more pauses during inhalation while awake, 3) They showed more variable breathing volumes during sleep, and 4) They had lower peak airflow during exhalation while awake. These differences were consistent enough to allow for accurate classification of who had anosmia just from their breathing patterns.
Study Limitations
The study had several constraints worth noting. The device couldn’t measure breathing through the mouth, only through the nose. The researchers also noted they would have preferred to measure breathing more frequently but were limited by battery life considerations. Additionally, they didn’t formally verify normal smell in the control group, relying instead on self-reporting. The study also focused only on people born without smell, not those who lost it later in life.
Discussion & Takeaways
The study suggests that breathing patterns might be more important for health than previously recognized. Each breath triggers a cascade of neural activity throughout the brain, meaning that people with normal smell experience hundreds more such neural waves per hour. These differences in breathing patterns might help explain why smell loss is associated with various health problems and reduced life expectancy.
The research also demonstrates that sophisticated measurement of breathing patterns might offer a new way to diagnose smell disorders without requiring smell tests. The findings raise important questions about whether people who lose their sense of smell later in life might also develop altered breathing patterns and whether these changes might contribute to health outcomes.
Funding & Disclosures
The research received funding from the Sagol Weizmann—MIT Bridge Program, The Minerva Foundation, and ERA PerMed JTC2019 under the project PerBrain. These grants have facilitated the in-depth exploration of anosmia and its broader impacts on health, as outlined in the study.
Furthermore, several authors of the study have financial interests related to the technologies used in their research. The nasal airflow measurement device central to this study is the subject of a patent application by The Weizmann Institute of Science, indicating a potential for commercial development. Moreover, some of the study’s authors have a financial stake in a startup company that is developing this nasal airflow measurement technology. It is important to note, however, that the startup company had no involvement in the current study, ensuring that the findings are presented without commercial bias.
