Olfactory function, neurofilament light chain, and cognitive trajectory: A 12‐year follow‐up of the Shanghai Aging Study

This study aimed to determine whether blood neurofilament light chain (NfL) modifies the association of olfactory dysfunction (OD) with long‐term cognitive decline. A total of 1125 non‐demented older adults in the Shanghai Aging Study were evaluated for baseline olfaction (12‐item Sniffin’ Sticks Smell Test) and cognitive trajectory by a 12‐year follow‐up. Baseline blood NfL was quantified using Single Molecular Array assay, and dichotomized into low and high levels based on the median value of concentration. The Mini‐Mental State Examination (MMSE) and Telephone Interview for Cognitive Status‐40 were used to assess participants’ cognitive function. Cognitive decline was ascertained when dementia was diagnosed or documented in the medical record during follow‐up, or the MMSE declining rate (slope) was 1.0 SD larger than the group mean. OD participants presented a steeper trajectory of MMSE score (p interaction = 0.004) and a high risk of cognitive decline (adjusted HR [95% CI], 1.82 [1.11, 2.98]) only in those with high NfL. Participants with combined OD and high NfL showed the highest risk of cognitive decline (adjusted HR, 2.43 [1.20, 4.92]). OD, especially in combination with high blood NfL concentration, may be able to identify individuals who later incur cognitive deterioration.