Association Between Olfactory Dysfunction and Mortality in US Adults

This cohort study investigates the association of olfactory dysfunction with all-cause 5-year mortality in US adults 40 years or older. Importance A study of olfactory dysfunction and mortality in a large national cohort will aid in better understanding their association when accounting for multiple relevant factors and possible underlying mechanisms. Objective To investigate the association of olfactory dysfunction with all-cause 5-year mortality in US adults. Design, Setting, and Participants This cohort study included participants 40 years or older from the 2013-2014 National Health and Nutritional Examination Survey who had data on olfaction and mortality (n = 3503). Olfaction was assessed by self-report and objective test (8-odor Pocket Smell Test). Mortality was determined by linking with the National Death Index through February 24, 2019. Data were analyzed from July 1 to September 30, 2019. Main Outcomes and Measures Olfaction and 5-year mortality. Cox proportional regression models were used to examine the associations between olfaction and mortality while adjusting for demographics and medical comorbidities. Multivariate models were further adjusted for depression and cognitive assessments. Results Among the 3503 participants (1831 women [52.3%]; mean [SD] age, 59.0 [12.0] years), the prevalence of olfactory dysfunction was 13.5% (95% CI, 11.0%-16.0%) based on results of an objective smell test and 21.6% (95% CI, 18.9%-24.2%) based on self-report. Risk of mortality increased by 18% (95% CI, 7%-29%) per 1-point decrease in smell test score in a multivariate model. The association was significant among adults 65 years or older in association with binary (hazard ratio [HR], 1.95; 95% CI, 1.19-3.21) and linear (HR, 1.19; 95% CI, 1.08-1.31) measures of objective olfactory dysfunction, but not among adults aged 40 to 64 years. There was no association between self-reported olfactory dysfunction and mortality. The association between objective olfactory dysfunction and mortality remained after further adjusting for cognitive assessment battery and depression among older adults (HR, 1.18; 95% CI, 1.01-1.37). Conclusions and Relevance These findings suggest that objective olfactory dysfunction is associated with increased mortality among older adults. In addition to its effect on quality of life, the association of olfactory dysfunction with mortality has implications for physical and cognitive health. Question Is self-reported and/or objectively measured olfactory dysfunction associated with mortality when accounting for relevant factors among adults in the United States? Findings In this nationally representative cohort study of 3503 adults 40 years or older, objectively measured olfactory dysfunction was significantly associated with increased all-cause 5-year mortality among older adults independent of demographics, cardiovascular comorbidities, depression, and cognition (18% increased risk per 1-point decrease in Pocket Smell Test score [score range, 0-8]). Self-reported olfactory dysfunction was not associated with mortality. Meaning These findings suggest that objectively measured olfactory dysfunction is robustly associated with 5-year mortality among older US adults, and olfaction measured by objective smell test may be a useful indicator of health status in older adults.