Olfactory dysfunction and cognition among older adults in the United States

In this work we assess the association between olfactory dysfunction and cognition in a nationally representative sample of older adults in the United States.

Participants aged ≥60 years (n = 1236) from the 2013-2014 National Health and Nutritional Examination Survey underwent both olfactory and cognitive testing. Olfaction was assessed by both objective test (8-odor Pocket Smell Test: smell impairment defined as score ≤2) and self-report. Cognitive assessment consisted of the Digit Symbol Substitution Test (DSST), the Animal Fluency Test, and the Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Regression models were used to examine the association between olfaction and cognition while adjusting for demographics, cardiovascular factors, and associated medical history.

The prevalence of smell impairment in US older adults was 18.0% (95% confidence interval [CI], 14.0-22.0%) and 22.0% (95% CI, 18.5-25.6%) based on objective smell test and self-report, respectively. In a multivariate model adjusted for relevant factors, low smell test scores were consistently associated with low scores on cognitive assessments, with a DSST score difference of -1.5 (95% CI, -2.2 to -0.8), Animal Fluency Test score difference of -0.4 (95% CI, -0.7 to -0.1), and CERAD Word List score difference of -0.4 (95% CI, -0.6 to -0.2) per 1-point decrease in smell test score. There was no association between self-reported smell impairment and cognition.

Objectively measured olfactory dysfunction is independently associated with cognitive impairment. These findings are consistent with previous studies and suggest the utility of objective olfactory tests as an indicator for cognitive impairment as compared with self-reported olfactory dysfunction, which is an uncertain indicator.