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Olfactory Dysfunction as a Marker of Cognitive Decline

DECLINE in cognitive function, including remembering, thinking, and reasoning, often accompanies the normal ageing process. However, a recent investigation has shown that an impaired sense of smell in adults aged 65–74 years may be used as a marker to identify those at risk of reduced cognitive function, allowing a diagnosis of neurodegenerative diseases before more obvious symptoms occur.

Building on a 2015 study that identified a link between decreased sense of smell and a decline in cognitive performance of study participants, researchers from Germany have now been the first to report on age-specific associations in the general population. The team analysed data from the Heinz Nixdorf Recall study, which included a total of 4,814 volunteers aged 45–75 years who were recruited from 2000–2003 and examined three times over a 10-year period. As part of the final examination, 2,640 participants with an average age of 68.2 years completed a Sniffin’ Sticks Screening Test alongside eight validated cognitive subtests. The group was classified into three subsectors according to sense of smell (scored 0–12): anosmic, or no sense of smell (score: ≤6), hyposmic, or impaired sense of smell (score: 7–10), or normosmic, or normal sense of smell (score: ≥11).

After analysing the cognitive results and the sense of smell scores using age and gender, the team noted that there was a significant difference in performance according to sense of smell in the 65–74-year age group; the worst cognitive test results were found in anosmic individuals, whereas the best performance was seen in participants with normal olfactory function. This pattern was also observed in the other age groups (55–64 years and 75–86 years); however, it was not a significant difference.

The results of this analysis may indicate that a reduced sense of smell can serve as an effective marker to identify those at a high risk of cognitive decline during older age. As a common symptom of dementia, identifying a marker of cognitive decline in dementia patients before other symptoms occur could result in improved management and care.