Olfaction and the 5-year incidence of cognitive impairment in an epidemiological study of older adults.

Objectives: To determine whether odor identification ability is associated with the 5-year incidence of cognitive impairment in a large population of older adults with normal cognition at baseline and whether olfactory impairment contributes to the prediction of cognitive decline.

Design: Population-based longitudinal study.

Setting: Beaver Dam, Wisconsin.

Participants: One thousand nine hundred twenty participants in the Epidemiology of Hearing Loss Study (mean age 66.9).

Measurements: Olfaction was measured using the San Diego Odor Identification Test (SDOIT). Incident cognitive impairment was defined as a Mini-Mental State Examination (MMSE) score of less than 24 or reported diagnosis of dementia or Alzheimer's disease (AD) at follow-up in participants with a MMSE score of 24 or greater and no diagnosis of dementia or AD at baseline.

Results: There was a significant association between olfactory impairment at baseline and 5-year incidence of cognitive impairment (odds ratio (OR)=6.62, 95% confidence interval (CI)=4.36-10.05). The association remained significant after adjusting for possible confounders (OR=3.72, 95% CI=2.31-5.99). The positive predictive value of the SDOIT was 15.9%, the negative predictive value was 97.2%, the sensitivity was 55.1%, and the specificity was 84.4% for 5-year incidence of cognitive impairment.

Conclusion: Olfactory impairment at baseline was strongly associated with 5-year incidence of cognitive impairment as measured using the MMSE. Odor identification testing may be useful in high-risk settings, but not in the general population, to identify patients at risk for cognitive decline.