In a Swedish study of adults aged 40 to 90 years who were followed for 10 years, poor smell was linked with an increased risk of dying.
During the study, 411 of 1,774 participants (23%) died. After controlling for demographic, health-related and cognitive confounders, each additional correctly identified odor lowered the risk of mortality by 8%. Individuals who performed at chance level on tests (indicating complete olfactory loss) were at a 19% higher risk of death than individuals with normal smell function.
The results contribute to the growing evidence that olfactory assessments might provide insights on the aging brain.
“Our results were not explained by dementia, which was previously linked to smell loss. Instead, mortality risk was uniquely predicted by smell loss,” said Dr Jonas Olofsson at the Gösta Ekman Laboratory, psychology department at Stockholm University in Stockholm and the Swedish Collegium for Advanced Study in Uppsala, and the senior author of the study.
“In our future research, we will try to pinpoint the biological processes that can explain this phenomenon.”
Objectives: To determine whether dementia could explain the association between poor olfactory performance and mortality risk within a decade-long follow-up period.
Design: Prospective cohort study.
Setting: Betula Study, Umeå, Sweden.
Participants: A population-based sample of adult participants without dementia at baseline aged 40 to 90 (N = 1,774).
Measurements: Olfactory performance using the Scandinavian Odor-Identification Test (SOIT) and self-reported olfactory function; several social, cognitive, and medical risk factors at baseline; and incident dementia during the following decade.
Results: Within the 10-year follow-up, 411 of 1,774 (23.2%) participants had died. In a Cox model, the association between higher SOIT score and lower mortality was significant (hazard ratio (HR) = 0.74 per point interval, 95% confidence interval (CI) = 0.71–0.77, P < .001). The effect was attenuated, but remained significant, after controlling for age, sex, education, and health-related and cognitive variables (HR = 0.92, 95% CI = 0.87–0.97, P = .001). The association between SOIT score and mortality was retained after controlling for dementia conversion before death (HR = 0.92, 95% CI = 0.87–0.97, P = .001). Similar results were obtained for self-reported olfactory dysfunction.
Conclusion: Poor odor identification and poor self-reported olfactory function are associated with greater likelihood of future mortality. Dementia does not attenuate the association between olfactory loss and mortality, suggesting that olfactory loss might mark deteriorating health, irrespective of dementia.
Ingrid Ekström, Sara Sjölund, Steven Nordin, Annelie Nordin Adolfsson, Rolf Adolfsson, Lars-Göran Nilsson, Maria Larsson, Jonas Olofsson