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.
In a study using data from nearly 1,200 older adults, Johns Hopkins Medicine researchers have added to a growing body of evidence that loss of the sense of smell is a predictive marker for an increased risk of frailty as people age. Building on previous research showing that olfactory dysfunction is a common early sign of brain-linked cognitive decline, the new findings suggest the link to frailty is likely not just in the brain but also in the nose itself.
If further studies affirm the findings, the researchers say, screening older adults’ ability to smell various scents could be as important as testing hearing and vision over time.
Results of the study, published Jan. 10 in the Journal of Gerontology, looked at the prevalence of frailty, an age-related syndrome of physiological decline, along with two different ways of assessing the ability to smell: olfactory sensitivity (the ability to detect an odor’s presence) and olfactory identification (the ability to detect and name an odor). Olfactory identification is a central measure of smell function, which has been linked to frailty and relies on higher-order cognitive processing to interpret and classify an odor. This suggests that neurological function may help to explain the relationship between smell and frailty. However, researchers say the ability to merely detect an odor without having to use higher-level neurological processes and the relationship of the ability to detect odors alone with frailty have been understudied.
Decline in sense of smell is connected to faster buildup of Alzheimer’s disease-related pathology seen in brain scans, according to new research focused on older adults who live outside of nursing homes. The findings provide additional evidence that loss of smell (known as anosmia) is a key early sign of Alzheimer’s-related cognitive impairment and the accumulation of associated harmful proteins, such as amyloid-beta and tau. The research, led by NIA scientists, was published in the Journal of Alzheimer’s Disease.
Decline in sense of smell had previously been confirmed as an early warning sign for Alzheimer’s in both human and animal studies, but its connection to the uptick of dementia-related brain imaging biomarkers over time had not been as closely studied in larger populations of older adults. For this study, the team tracked 364 participants from the Baltimore Longitudinal Study of Aging (BLSA) over an average period of about 2.5 years. The NIA-led BLSA is the longest running study of healthy aging in America.
Contrary to what science once suggested, older people with a declining sense of smell do not have comprehensively dampened olfactory ability for odors in general – it simply depends upon the type of odor. Researchers at the University of Copenhagen reached this conclusion after examining a large group of older Danes’ and their intensity perception of common food odors.
That grandpa and grandma aren’t as good at smelling as they once were, is something that many can relate to. And, it has also been scientifically demonstrated. One’s sense of smell gradually begins to decline from about the age of 55. Until now, it was believed that one’s sense of smell broadly declined with increasing age. However, a study from the University of Copenhagen reports that certain food odors are significantly more affected than others.
The Department of Food Science’s Eva Honnens de Lichtenberg Broge and her fellow researchers have tested the ability of older Danes to perceive everyday food odors. The researchers measured how intensely older adults perceived different food odours, as well as how much they liked the odours.