Predictors of Olfactory Decline in Aging: A Longitudinal Population-Based Study

Abstract

Background Olfactory dysfunction is common in aging and associated with dementia and mortality. However, longitudinal studies tracking change in olfactory ability are scarce. We sought to identify predictors of interindividual differences in rate of olfactory identification change in aging Methods Participants were 1,780 individuals, without dementia at baseline and with at least two olfactory assessments over 12 years of follow-up (mean age = 70.5 years; 61.9% female), from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). Odor identification was assessed with the Sniffin’ Sticks. We estimated the impact of demographic, health, and genetic factors on rate of olfactory change with linear mixed effect models Results Advancing age, manufacturing profession, history of cerebrovascular disease, higher cardiovascular disease burden, diabetes, slower walking speed, higher number of medications, and the APOE ε4 allele were associated with accelerated odor identification decline (ps < 0.014). Multi-adjusted analyses showed unique associations of age, diabetes, and ε4 to olfactory decline (ps < 0.017). In 1,531 participants who remained free of dementia (DSM IV criteria) during follow-up, age, cardiovascular disease burden, and diabetes were associated with accelerated decline (ps < 0.011). Of these, age and diabetes remained statistically significant in the multi-adjusted model (ps < 0.001) Conclusion Demographic, vascular, and genetic factors are linked to rate of decline in odor identification in aging. Although some olfactory loss may be an inevitable part of aging, our results highlight the importance of vascular factors for the integrity of the olfactory system, even in the absence of dementia

Serum C-Reactive Protein Is Negatively Associated With Olfactory Identification Ability in Older Adults

“…The lack of statistical significance was likely attributable to the small sample size with resulting low power in this group. Although olfactory function decreased significantly as a function of time (annual change rate of À0.213; p < .001), as described in detail elsewhere (Ekstr€ om et al, 2020), no statistically significant associations between CRP levels at baseline and olfactory change were observed (ps > .406).…”

“…Interestingly, sensitivity analyses showed that associations between CRP and olfactory function were confined to participants aged 72 years and below and males. Increasing age is a principal cause for olfactory loss (Doty & Kamath, 2014;Ekstr€ om et al, 2020), which may over-shadow potential effects of inflammatory processes on olfactory ability in older age groups. Alternatively, and as mentioned earlier, potential influences of inflammation on olfaction may be exerted before a certain age.…”

“…Odor identification was measured with the Sniffin' Sticks, a well-established and normreferenced olfactory test kit with high test-retest reliability (Hummel et al, 1997(Hummel et al, , 2007Croy et al, 2015). The testing procedure has been described in detail elsewhere (Ekstr€ om et al, 2020). In brief, participants were presented with 16 household odors and instructed to freely identify the presented odor by providing a verbal descriptor (free identification).…”

Olfaction and Aging: A Review of the Current State of Research and Future Directions

“…The most common etiologies of olfactory disorders among patients seeking medical attention at ear, nose, and throat clinics include upper respiratory infection, chronic sinusitis, nasal polyposis, allergic rhinitis, and head trauma ( Brämerson et al., 2007 ; Temmel et al., 2002 ). The presence of type-2 diabetes accelerates age-related olfactory decline ( Ekström et al., 2020 ; Olofsson et al., 2010 ). Given the profound impact of such conditions on the olfactory system, it is not surprising that environmental variables overshadow genetic variables in their effects of olfactory abilities among aging individuals ( Doty & Kamath, 2014 ; Rawson, 2006 ).…”

Olfaction and aging: A review of the current state of research and future directions

“…The most common etiologies of olfactory disorders among patients seeking medical attention at ear, nose and throat clinics include upper respiratory infection, chronic sinusitis, nasal polyposis, allergic rhinitis, and head trauma (Temmel et al, 2002;Brämerson et al, 2007). The presence of type-2 diabetes accelerates age-related olfactory decline (Ekström et al, 2020;Olofsson et al, 2010). Given the profound impact of such conditions on the olfactory system, it is not surprising that environmental variables overshadow genetic variables in their effects of olfactory abilities among older individuals (Rawson, 2006;Doty and Kamath, 2014).…”