Olfactory Dysfunction Associated with Increased Mortality Especially in Those with Dementia

Results of a longitudinal study published in JAMA Otolaryngology–Head and Neck Surgery demonstrated a significant association between olfactory dysfunction and increased mortality risk among older adults, particularly for deaths related to neurodegeneration. 
The study, part of the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), included 2524 participants aged 60 to 99 years. Baseline assessments were conducted between 2001 and 2004. Researchers monitored participants over 12 years and measured olfactory ability using the 16-item Sniffin’ Sticks test (Burghardt, Wedel, Germany). Mortality data were obtained from the Swedish National Cause of Death Register. Researchers utilized Cox proportional hazards models to evaluate the relationship between olfaction and mortality over 6 and 12 years, and competing risk regression and generalized structural equation models were used to assess specific causes of death and mediating factors such as incident dementia, chronic diseases, frailty, and malnutrition.

Key results include the following:
•    Compared to survivors, mean baseline odor identification performance was 2.34 points (95% CI, 1.99 to 2.69) lower among those who died at 6 years and 2.33 points (95% CI, 2.08 to 2.58) lower among those who died at 12 years.
•    Each additional incorrect answer on the odor identification test was associated with a 6% higher risk of all-cause mortality at 6 years (hazard ratio [HR] 1.06; 95% CI, 1.03 to 1.08) and a 5% higher risk at 12 years (HR 1.05; 95% CI, 1.03 to 1.08) in multiadjusted models.
•    Meaningful mediators for death at 6 years included dementia (23% of total association), frailty (11%), and malnutrition (5%). At 12 years, frailty remained a mediator (9% of total association) at 12 years. 
These results suggest that olfactory assessments may have clinical utility in identifying older adults at heightened risk for adverse outcomes and mortality, although study authors note that further research is needed to clarify underlying mechanisms and inform targeted interventions.