Neurofilament light chain is associated with olfactory dysfunction in US adults: findings from National Health and Nutrition Examination Survey

Background: Many individuals who have olfactory dysfunction are not aware of their impairment, which results in delayed detection of potentially hazardous situations. Simple and accurate methods for objectively assessing olfactory function are needed. In this study, we aim to investigate the utility of serum neurofilament light chain (NfL) levels as an indicator of olfactory dysfunction. Methodology: We analysed data on 1290 participants aged 40 years and older, who had valid data on olfaction and NfL level from the National Health and Nutrition Examination Survey 2013–2014. Multivariable modeling was used to investigate the relationship between olfactory dysfunction and NfL. Results: Among 1290 participants, 174 participants had olfactory dysfunction based on the results of the NHANES Pocket Smell Test. In ordinal regression models, objective olfactory dysfunction was associated with NfL. After adjusting for age, sex, race/ethnicity, diabetes, smoking, olfaction-related medical history, Parkinson's disease and Alzheimer’s disease, the association remained significant. In logistic regression models, compared to participants with lower levels of NfL in the first tertile, those in the second and third tertiles had higher odds of objective olfactory dysfunction. There was no association between self-reported olfactory dysfunction and NfL tertiles. Conclusions: A strong association between objective olfactory dysfunction and serum NfL level was observed. NfL, independent of age, is a reliable marker indicating the development of olfactory dysfunction. The measurement of serum NfL level provides valuable support for assessment of olfactory dysfunction in clinical practice.