The association between olfactory impairment and total mortality in older adults

Population-based data on the relationship between impaired olfaction and risk of mortality among older adults are lacking. We used a representative cohort of adults aged 60 years or older to assess whether olfactory loss is a predictor of mortality, independent of potential confounders.

Olfaction was measured by the San Diego Odor Identification Test (SDOIT) among 1,636 participants enrolled in the Blue Mountains Eye Study (2002-2004). Five-year all-cause mortality was confirmed using the Australian National Death Index.

More than one in five participants (21.8%) with olfactory impairment had died over the 5 years compared with less than 10% of participants without olfactory loss. Moderate olfactory loss (SDOIT score ≤3) was associated with a 68% increased risk of all-cause mortality (multivariable-adjusted hazard ratio, 1.68; 95% confidence interval, 1.10-2.56). This association did not persist after further adjustment for cognitive impairment. The association between olfactory loss and all-cause mortality was more marked among older participants (≥70 years) than younger participants (<70 years) with olfactory impairment (multivariable-adjusted hazard ratio, 1.48; 95% confidence interval, 1.02-2.15). However, adjusting for cognitive impairment diminished this association.

Older adults with moderately impaired olfaction compared with those with normal olfaction had a higher risk of dying 5 years later. The relationship between olfaction and mortality, however, may be largely mediated by cognitive impairment in these older adults. Our findings highlight the value of identifying olfactory loss in the preclinical stage in the older patient before the development of related comorbidities.