Researchers here show that the distribution of microbial populations in the nasal microbiome correlates with mild cognitive impairment and age-related loss of sense of smell. Both of these are manifestations of neurodegenerative processes that degrade function in the central nervous system. While we know that age-related changes in the gut microbiome are probably influential on age-related conditions via, at the very least, provoking increased chronic inflammation. But is the nasal microbiome large enough to have the same sort of effect on the function of parts of the brain? It seems more plausible that both nasal microbiome and neurodegeneration are influenced by the state of the aging immune system. Either way, more research is needed if a concrete answer is wanted.
Emerging evidence has highlighted that olfactory dysfunction, a common feature of aging, is increasingly linked to cognitive decline in older adults. However, research on the underlying mechanism, particularly the role of nasal microbiome, remains limited. In this study, we investigated the associations between olfactory function, the nasal microbiome, and cognition among 510 older adults with an average age of 77.9 years. Olfactory function was assessed using the brief Chinese Smell Identification Test, and cognitive assessments were conducted via the Mini-Mental State Examination and the Revised Hasegawa Dementia Scale. Nasal microbiome profiles were generated through 16S rRNA gene sequencing.
We observed that olfactory dysfunction (i.e., hyposmia) was associated with a higher richness of nasal bacteria, and such observation was replicated in an external dataset. A total of 18 nasal bacterial genera were identified to be associated with olfactory function, with eight genera such as Acidovorax and Morganella being enriched in the hyposmic group. A composite microbial index of nasal olfactory function significantly improved the reclassification accuracy of traditional risk model in distinguishing hyposmic from normosmic participants. Furthermore, participants with a nasal biotype dominated by Corynebacterium had a lower prevalence of mild cognitive impairment compared to those dominated by Dolosigranulum or Moraxella.
Our findings suggested that the nasal microbiome may play a role in the association of olfactory function with cognition in older adults, providing new insights into the microbial mechanisms underlying hyposmia and cognitive decline.
Link: https://doi.org/10.1038/s41398-025-03346-y
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