Sense of smell linked to speed of brain loss and cognitive decline
Having a good sense of smell is associated with slower loss of brain volume and cognitive decline in older adults, and the link between sense of smell and brain and cognitive changes may be especially pronounced among those who develop cognitive impairment or dementia. These are the key findings from NIA-led research published recently in Neurology.
The sense of smell declines with age, and loss of olfactory function is also an early symptom of neurodegenerative diseases such as Parkinson’s and Alzheimer’s. While previous research found the sense of smell was associated with brain volume and function, no studies had examined longitudinal changes within an individual across the whole brain and by cognitive status.
In this study, scientists analyzed sense of smell, brain imaging, and cognitive performance data from participants in the NIA Baltimore Longitudinal Study of Aging. The researchers examined whether sense of smell, as reflected by odor identification scores, was associated with longitudinal changes in regional brain volumes and changes to cognitive function. To examine the association between sense of smell and brain volume, they compared odor identification scores and brain MRI scans from a subset of 567 participants. The association between sense of smell and cognitive function was analyzed by comparing odor identification scores and cognitive evaluations from a subset of 754 participants. The subsets were analyzed separately but included 565 overlapping participants with both brain MRI scans and cognitive assessment data.
Participants who developed cognitive impairment or dementia had worse odor identification scores than those who did not. Better odor identification scores were associated with slower loss of brain volume, particularly in the frontal and temporal regions — areas important for thinking and memory. Better scores were also associated with slower decline in memory, attention, processing speed, and sensorimotor integration skills over time. However, when data points after a diagnosis of cognitive impairment or dementia were excluded from analysis, the associations between sense of smell with brain volume and cognitive functioning were not as strong.
These study findings add to evidence that sense of smell is related to cognitive impairment and dementia and demonstrate longitudinal relationships with brain volume loss in specific brain areas and cognitive decline in specific domains. Future studies with longer follow-ups of change over time may help researchers better understand the potential for using sense of smell as an early biomarker of cognitive decline and the role of specific brain regions in this association.
These activities relate to NIH’s Alzheimer’s and Related Dementias Research Implementation Milestones:
- 2.A, “Create new research programs that use data-driven, systems-based approaches to integrate the study of fundamental biology of aging with neurobiology of aging and research on neurodegeneration, AD and AD-related dementias to better understand the mechanism(s) of vulnerability and resilience in AD across all levels of biologic complexity (from cellular to population level) and to gain a deeper understanding of the complex biology and integrative physiology of healthy and pathologic brain aging.”
- 9.M, “Develop diagnostics/biomarkers in asymptomatic individuals.”
Reference: Tian Q, et al. Associations of olfaction with longitudinal trajectories of brain volumes and neuropsychological function in older adults. Neurology. 2023. Epub Dec. 2, 2022. doi: 10.1212/WNL.0000000000201646.