The Association of Allergy-Related and Non-Allergy-Related Olfactory Impairment with Cognitive Function in Older Adults: Two Cross- Sectional Studies.

Background: Evidence on the association of Olfactory Impairment (OI) with age-related cognitive decline is inconclusive, and the potential influence of allergy remains unclear.

Objective: We aimed to evaluate the cross-sectional associations of allergy-related and non-allergy- related OI to cognitive function.

Methods: We included 2,499 participants from the Health and Retirement Study (HRS)-Harmonized Cognitive Assessment Protocol (HCAP) sub-study and 1,086 participants from the English Longitudinal Study of Ageing (ELSA)-HCAP. The Olfactory Function Field Exam (OFFE) using Sniffin' Stick odor pens was used to objectively assess olfactory function and an olfactory score <6/11 indicated OI. Mini-Mental Status Examination (MMSE) was used to assess global cognitive function and define cognitive impairment (<24/30). A neuropsychologic battery was used to assess five cognitive domains.

Results: Compared to non-OI participants, individuals with OI had lower MMSE z-score [β_HRS = -0.33, 95% Confidence Interval (CI): -0.41 to -0.24; β_ELSA = -0.31, -0.43 to -0.18] and higher prevalence of cognitive impairment (Prevalence Ratio (PR)HRS = 1.46, 1.06 to 2.01; PR_ELSA = 1.63, 1.26 to 2.11). The associations were stronger for non-allergy-related OI (β_HRS = -0.36; β_ELSA = -0.34) than for allergy-related OI (β_HRS = -0.26; β_ELSA = 0.13). Similar associations were observed with domain- specific cognitive function measures.

Conclusion: OI, particularly non-allergy-related OI, was related to poorer cognitive function in older adults. Although the current cross-sectional study is subject to several limitations, such as reverse causality and residual confounding, the findings will provide insights into the OI-cognition association and enlighten future attention to non-allergy-related OI for the prevention of potential cognitive impairment.