Objective: To investigate the relationship between impairment in smell and cognitive function among older adults using both self-report and objective measurement of olfactory function.

Background: Due to significant health and socioeconomic impact of cognitive impairment, it is important to discover easily accessible markers or predictors of cognitive decline for early detection and intervention. Prior studies have suggested that impairment in smell is associated with neurodegenerative disorders such as Parkinson disease and normal aging. However, it is uncertain if smell dysfunction is a predictive factor of cognitive impairment in older individuals.

Methods: This is a cross-sectional study using public data from the National Health and Nutrition Examination Survey (NHANES, 2013-2014) conducted on a nationally representative sample of the US population. Cognitive function was assessed using the Digit Symbol Substitution Test (DSST) in adults (60+ years). Olfactory function was assessed using self-reported questionnaires and Pocket Smell Test (PST). Other covariates include age, sex, education level, smoking, history of head trauma. Bivariate relationships were assessed with chi-square. Linear regression was used to assess relationship between continuous outcome variable and predictor variables.

Results: The total analytic sample included 1592 subjects, 52.1% female, mean age of 69.6 years (SD 6.7). Mean score on DSST was 45.95 (SD 17.23). 134/1592 (8.42%) reported subjective hyposmia, 382/1592 (24.0) were tested either hyposmia or anosmia on objective PST (p<0.001). Subjects with objective hyposmia and anosmia were associated with a significant decrease in cognitive test score on DSST as compared to subjects with normal sense of smell (p<0.001). For every one year increase in age, there is significant reduction points on cognitive test (p<0.001). Male subjects are associated with a significant decrease on cognitive test compared to female subjects (p<0.001). High school and college graduates are associated with a significant increase on cognitive test compared with below high school education (p<0.001). Subjective hyposmia, history of loss of consciousness, history of smoking, and history of serious skull injury were found to be not significantly associated with cognitive test score.

Conclusions: There is a discrepancy between self report and objective measurement of olfactory function in older individuals. Hyposmia and anosmia measured objectively as opposed to by self report, along with male sex, age, below high school education, are statistically significant predictors for decreased cognitive function.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/olfactory-dysfunction-predicting-cognition/