Environmental Air Pollution and Olfactory Decline in Aging

Abstract

Background: Olfactory impairment is increasingly common with older age, which may be in part explained by cumulative effects of exposure to inhaled toxins. However, population-based studies investigating the relationship between air pollution and olfactory ability are scarce.

Objectives: We aimed to investigate associations between exposure to common air pollutants and longitudinal change in odor identification.

Methods: Our study of 2,468 participants ($\text{mean age}=72.3y$; 61.1% female), of which 1,774 participants ($\text{mean age}=70.5y$; 61.9% female) had at least two olfactory assessments over 12 y of follow-up from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), Stockholm, Sweden. Participants were free from cognitive impairment and neurodegenerative disease at baseline. Odor identification ability was assessed with Sniffin' Sticks. Change in olfactory performance was estimated with linear mixed models. Exposure to two major airborne pollutants [particulate matter with aerodynamic diameter $\le 2.5\mu m$ (${\mathrm{PM}}_{2.5}$) and nitrogen oxides (${\mathrm{NO}}_x$)] for the 5 y preceding baseline was assessed using spatiotemporal dispersion models for outdoor levels at residential addresses.

Results: Participants showed significant decline in odor identification ability for each year in the study {$\beta =-0.20$ [95% confidence interval (CI): $-0.22$, $0.18$; $p<0.001$]}. After adjustment for all covariates, residents of third [$\beta =-0.09$ (95% CI: $-0.14$, $-0.04$; $p<0.001$)] and fourth [$\beta =-0.07$ (95% CI: $-0.12$, $-0.02$; $p=0.005$)] exposure quartiles of ${\mathrm{PM}}_{2.5}$ had faster rates of olfactory decline than residents from the first quartile. Similar results were observed for the third [$\beta =-0.05$ (95% CI: $-0.10$, $-0.01$; $p=0.029$)] and fourth [$\beta =-0.07$ (95% CI: $-0.11$, $-0.02$; $p=0.006$) quartiles of ${\text{NO}}_x$].

Discussion: Our results suggest an association between air pollution exposure and subsequent olfactory decline. We speculate that cumulative effects of airborne pollutants on the olfactory system may be one underlying cause of olfactory impairment in aging. https://doi.org/10.1289/EHP9563.

Figure 1.

The SNAC-K study design.

Figure 2.

Results of multiadjusted linear mixed models (adjusted for age, sex, education, odor test version at baseline, baseline assessment year, vocabulary, longest held occupation, BMI, smoking, diabetes, heart disease, and cerebrovascular disease) on associations between quartiles of air pollution in ${\mathrm{PM}}_{2.5}$ (5-y mean prior baseline assessment) and intercept and change (score/year) in odor identification in the total sample ($n=\mathrm{2,468}$), derived from the SNAC-K study on Aging and Care in Kungsholmen, Stockholm, Sweden (baseline assessment between 2001 and 2003; last assessment between 2013 and 2015).

Figure 3.

Results of multiadjusted linear mixed models (adjusted for age, sex, education, odor test version at baseline, baseline assessment year, vocabulary, longest held occupation, BMI, smoking, diabetes, heart disease, and cerebrovascular disease) on associations between quartiles of air pollution in ${\mathrm{NO}}_{\mathrm{x}}$ (5-y mean prior baseline assessment) and intercept and change (score/year) in odor identification in the total sample ($n=\mathrm{2,468}$), derived from the SNAC-K Study on Aging and Care in Kungsholmen, Stockholm, Sweden (baseline assessment between 2001 and 2003; last assessment between 2013 and 2015).