Nasal Microbiome Influences Link Between Sense of Smell and Cognitive Health in Older Adults

As individuals age, particularly beyond middle age, changes in brain function, memory, and cognition become more evident, with many experiencing varying degrees of decline. This trend has led researchers to investigate potential underlying factors contributing to cognitive deterioration, including neurodegenerative diseases like dementia, which has seen a significant increase over recent decades. Projections indicate that the global number of dementia cases may rise from 55 million in 2019 to an estimated 139 million by 2050, underscoring the importance of early detection and intervention.

Recent studies have established a connection between olfactory function—the ability to perceive and identify odors—and cognitive abilities in older adults. While it is well-documented that olfactory dysfunction often correlates with declining cognitive health, the causality behind this relationship remains unclear. Researchers are exploring whether olfactory deficits directly influence cognitive decline or if both are consequences of common aging or neurodegenerative processes.

In a groundbreaking study conducted by scientists at Fudan University in China, researchers examined how the nasal microbiome—the community of microorganisms residing in nasal passages—might play a role in this link between olfactory function and cognition. Published in Translational Psychiatry, the study suggests that variations in nasal microbial communities could contribute to the decline in smell perception and cognitive performance.

The study involved 510 older adults, with an average age of 77.9 years. Researchers assessed their olfactory abilities using the brief Chinese smell identification test, while cognitive function was evaluated through standardized tests like the mini-mental state examination and the Hasegawa dementia scale. Nasal microbiomes were analyzed via 16S RNA gene sequencing to identify bacterial profiles.

Findings indicated that olfactory dysfunction, or hyposmia, was associated with increased diversity (richness) of bacteria in the nasal passages. Specifically, eight bacterial genera, including Acidovorax and Morganella, were found to be more prevalent in individuals with diminished olfactory function. Importantly, the research unveiled significant correlations between certain nasal bacterial profiles and varying degrees of cognitive impairment. Participants with a nasal biotype dominated by bacteria such as Corynebacterium were less likely to have mild cognitive impairment (MCI) compared to those with other bacterial dominance patterns like Dolosigranulum or Moraxella.

These results imply that the bacterial composition of the nasal microbiome may influence or reflect the connection between olfactory function and cognitive health in aging populations. The study’s microbial index improved the accuracy of predicting olfactory dysfunction beyond traditional risk models.

Overall, this emerging evidence supports the idea that nasal bacteria might play a role in the neurobiological processes underlying cognitive decline. Future research focusing on manipulating or modifying nasal microbiomes could open new avenues for early detection and targeted therapies aimed at preserving cognitive function in older adults.

Source: https://medicalxpress.com/news/2025-04-nasal-microbiome-link-olfactory-dysfunction.html