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.