Olfactory Deficits and Mortality in Older Adults

Abstract

Importance: Olfactory deficits are associated with higher mortality in older adults, but the mechanisms remain unclear. Further understanding this relationship could inform interventions to improve survival and quality of life for those with olfactory deficits.

Objective: To investigate the association of olfactory deficits with all-cause and cause-specific mortality and to explore potential mediating factors.

Design, setting, and participants: The Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), is an ongoing population-based, longitudinal cohort study with baseline between 2001 and 2004. Eligible participants were residents of Kungsholmen, Stockholm, Sweden, and aged between 60 and 99 years from March 21, 2001, to August 30, 2004. Twelve-year follow-up was completed in February 2013. Data analysis took place between February 2024 and July 2024.

Main outcomes and measures: Olfactory ability was tested with the 16-item Sniffin' Sticks Odor Identification task. Mortality was determined through the Swedish National Cause of Death Register. Cox proportional hazards models examined the associations between olfaction and mortality over 6 years and 12 years. Competing hazard risks regression analyses assessed the olfactory-mortality association for specific death causes. Generalized structural equation models investigated mediators, including incident dementia, baseline chronic diseases, frailty, and malnutrition. The tested hypotheses were formulated after data collection.

Results: Among 2524 participants (baseline mean [SD] age, 71.9 [10.0] years; 1545 [61.2%] female), 445 (17.6%) had died at 6 and 969 (38.4%) at 12 years of follow-up. Each additional incorrect answer on the odor identification test was associated with a 6% increased all-cause mortality risk at 6 years (hazard ratio [HR], 1.06 [95% CI, 1.03-1.08]) and 5% increased risk at 12 years (HR, 1.05 [95% CI, 1.03-1.08]) in multiadjusted models. In cause-specific models, the olfaction-mortality association had the greatest risk in relation to neurodegenerative death causes. Meaningful mediators for death at 6 years included dementia (23% of total association), frailty (11% of total association), and malnutrition (5% of total association). At 12 years, frailty remained a mediator (9% of total association).

Conclusions and relevance: The results of this cohort study underscore the importance of olfactory function as a mortality risk marker in older adults and highlight the evolving influence of neurodegeneration and frailty on this relationship. Further research is needed to assess the clinical utility of olfactory assessments in identifying individuals at risk of adverse health outcomes.

Figure 1.. Mediators of the Olfaction-Mortality Association at 6 Years

Path diagram of associations analyzed in the structural equation model, showing mediators with meaningful pathways linking olfaction to increased mortality at 6 years. Arrows indicate pathways with standardized coefficients representing the estimated associations. Percentages inside mediator boxes represent the proportion of the total estimated association mediated, calculated by multiplying the coefficients for the reversed olfactory score–mediator and mediator-mortality associations, dividing the mediated association by the total association, and multiplying by 100.

Figure 2.. Mediators of the Olfaction-Mortality Association at 12 Years

Path diagram of the estimated associations analyzed in the structural equation model, showing mediators with meaningful pathways linking olfaction to increased mortality at 12 years. Arrows indicate pathways with standardized coefficients representing the estimated associations. Percentages inside mediator boxes represent the proportion of the total estimated association mediated, calculated by multiplying the coefficients for the reversed olfactory score–mediator and mediator-mortality associations, dividing the mediated association by the total association, and multiplying by 100.