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Air pollution and dementia in a low exposure setting: the role of noise, olfaction, and theapoe gene
Umeå University, Faculty of Social Sciences, Department of Psychology.
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Previous research indicates an association between air pollution exposure, and risk of dementia. Still, a number of factors that may play a role in this association remain to be explored. In addition, while most studies on air pollution and brain health have taken place in highly exposed large urban areas, the studies included in this thesis are conducted in an area with relatively low levels of air pollution and road traffic noise.

The overall aim of this thesis is to investigate possible mechanisms - more specifically the role of noise, olfaction and the APOE-ε4 allele - in the association between air pollution and dementia, in a low exposure area. Because olfactory deficits have been linked to air pollution, and can be an early sign of dementia, an additional aim is to examine associations between exposure to air pollution and olfactory function.

Methods: Participants were drawn from the Betula project – a prospective cohort study – in Umeå, Sweden. Modelled data on concentrations of nitrogenoxides (NOx), fine particle matter (PM2.5) and levels of road traffic noise, were matched with participants residential address at baseline. PM2.5 levels at the day of testing were obtained from a measuring station in the vicinity of the test location. Data on dementia diagnoses, APOE status, olfactory functions, and covariates, were drawn from the Betula project. Dementia assessment was primarily based on medical records, and conducted by a geropsychiatrist. Odor identification was assessed using the Scandinavian Odor Identification Test, and odor detection threshold by “sniffin’ sticks”. APOE genotype was determined by DNA analyses of blood samples.

Study I. Where there is pollution, there is also often noise. In addition, exposure to noise can increase the risk of dementia. The aim of study I was to investigate the individual and combined effect of noise and air pollution on risk of dementia. The results showed an association between NOx and dementia. However, noise from road traffic did not contribute to this association.

Study II. Olfactory deficits can be an early sign of dementia and might also becaused by air pollution. Olfactory receptor cells in the nasal cavity are exposed to inhaled air, and the olfactory bulb is one of the areas of the brain most affectedby air pollution. The APOE-ε4 allele is important to consider, as it is a risk factor for both dementia and declining olfactory functions. The aim of study II was to investigate the role of olfaction and the APOE-ε4 allele in the association between air pollution and dementia. Stratified analyses showed that associations between PM2.5 and dementia persisted only among APOE-ε4 carriers, and those with poor odor identification ability.

Study III. The olfactory system may be vulnerable to air pollution, and olfactory dysfunction is an early sign of dementia. In addition, the moderating effect of odor identification ability found in study II, could be explained by air pollution increasing the risk of olfactory functions and dementia independent of each other. Thus, the aim of study III was to investigate the associations between PM2.5 (both long term exposure, and concentrations on the day of testing), and odor identification and detection. A positive association was observed between longterm air pollution exposure and odor identification ability. No association was found between long term air pollution exposure and odor detection, or between short term exposure and either olfactory outcome.

Conclusion: Low levels of long-term exposure to air pollution increases the risk of dementia. APOE-ε4 carriers, and those with poor odor identification ability, seem particularly vulnerable. No residual confounding from road traffic noisewas found, suggesting that air pollution is the main component in the association between traffic related exposures and dementia in low-exposure areas. The positive association between air pollution and odor identification might be explained by socioeconomic status, and the links between olfaction and semantic memory.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2023. , p. 52
Keywords [en]
Air pollution, Road traffic, NOx, dementia, APOE, Alzheimer’s disease, Apolipoprotein E, olfaction, particulate matter, vascular dementia, odor identification, odor detection
National Category
Psychology
Research subject
Psychology
Identifiers
URN: urn:nbn:se:umu:diva-205124ISBN: 978-91-8070-020-7 (print)ISBN: 978-91-8070-021-4 (electronic)OAI: oai:DiVA.org:umu-205124DiVA, id: diva2:1738876
Public defence
2023-03-24, SAM.A.247, Samhällsvetarhuset, Umeå, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas, 942-2015-1099Available from: 2023-03-03 Created: 2023-02-23 Last updated: 2023-02-23Bibliographically approved
List of papers
1. Road traffic noise, air pollution, and risk of dementia: results from the Betula project
Open this publication in new window or tab >>Road traffic noise, air pollution, and risk of dementia: results from the Betula project
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2018 (English)In: Environmental Research, ISSN 0013-9351, E-ISSN 1096-0953, Vol. 166, p. 334-339Article in journal (Refereed) Published
Abstract [en]

Background: There is growing evidence for a negative impact of traffic-related air pollution on risk of dementia. However, the contribution of noise exposure to this association has been rarely examined.

Objective: We aimed to investigate the individual and combined effect of noise and air pollution on risk of dementia.

Methods: Data on dementia incidence over a 15 year period was obtained from the Betula project, a longitudinal study on health and ageing. Estimates of annual mean levels of nitrogen oxides (NOx) at the participants’ residential address were obtained using a land-use regression model. Modelled data provided road traffic noise levels (Leq. 24 h) at the participants’ residential address at baseline. Cox proportional hazard regression was used to calculate hazard ratios (HR).

Results: Of 1721 participants at baseline, 302 developed dementia during the follow up period. Exposure to noise levels (Leq. 24 h) > 55 dB had no significant effect on dementia risk (HR 0.95; CI: 0.57, 1.57). Residing in the two highest quartiles of NOx exposure was associated with an increased risk of dementia. The risk associated with NOx was not modified by adjusting for noise. Moreover, we found no significant interaction effects between NOx and road traffic noise on dementia risk.

Conclusion: We found no evidence that exposure to road traffic noise, either independently or in combination with traffic air pollution, was associated with risk of dementia in our study area. Our results suggest that pollution should be considered the main component in the association between traffic related exposures and dementia.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Epidemiology, Alzheimer's disease, Vascular dementia, Land-use regression model
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:umu:diva-149090 (URN)10.1016/j.envres.2018.06.008 (DOI)000445318200035 ()29909174 (PubMedID)2-s2.0-85048442726 (Scopus ID)
Available from: 2018-06-15 Created: 2018-06-15 Last updated: 2024-04-08Bibliographically approved
2. Pm2.5 and dementia in a low exposure setting: the influence of odor identification ability and APOE
Open this publication in new window or tab >>Pm2.5 and dementia in a low exposure setting: the influence of odor identification ability and APOE
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2023 (English)In: Journal of Alzheimer's Disease, ISSN 1387-2877, E-ISSN 1875-8908, Vol. 92, no 2, p. 679-689Article in journal (Refereed) Published
Abstract [en]

Background: Growing evidence show that long term exposure to air pollution increases the risk of dementia.

Objective: The aim of this study was to investigate associations between PM2.5 exposure and dementia in a low exposure area, and to investigate the role of olfaction and the APOE ε4 allele in these associations.

Methods: Data were drawn from the Betula project, a longitudinal study on aging, memory, and dementia in Sweden. Odor identification ability was assessed using the Scandinavian Odor Identification Test (SOIT). Annual mean PM2.5 concentrations were obtained from a dispersion-model and matched at the participants’ residential address. Proportional hazard regression was used to calculate hazard ratios.

Results: Of 1,846 participants, 348 developed dementia during the 21-year follow-up period. The average annual mean PM2.5 exposure at baseline was 6.77 µg/m3, which is 1.77 µg/m3 above the WHO definition of clean air. In a fully adjusted model (adjusted for age, sex, APOE, SOIT, cardiovascular diseases and risk factors, and education) each 1 µg/m3 difference in annual mean PM2.5-concentration was associated with a hazard ratio of 1.23 for dementia (95% CI: 1.01–1.50). Analyses stratified by APOE status (ε4 carriers versus non-carriers), and odor identification ability (high versus low), showed associations only for ε4 carriers, and for low performance on odor identification ability.

Conclusion: PM2.5 was associated with an increased risk of dementia in this low pollution setting. The associations between PM2.5 and dementia seemed stronger in APOE carriers and those with below average odor identification ability.

Place, publisher, year, edition, pages
IOS Press, 2023
Keywords
Alzheimer’s disease, Apolipoprotein E, olfaction, particulate matter, vascular dementia
National Category
Occupational Health and Environmental Health
Research subject
Psychology; Occupational and Environmental Medicine
Identifiers
urn:nbn:se:umu:diva-205123 (URN)10.3233/jad-220469 (DOI)000952023800024 ()36776047 (PubMedID)2-s2.0-85151044242 (Scopus ID)
Funder
EU, Horizon 2020, 814978-2Swedish Research Council Formas, 942-2015-1099
Available from: 2023-02-23 Created: 2023-02-23 Last updated: 2024-04-08Bibliographically approved
3. PM2.5 exposure and olfactory functions
Open this publication in new window or tab >>PM2.5 exposure and olfactory functions
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2022 (English)In: International Journal of Environmental Health Research, ISSN 0960-3123, E-ISSN 1369-1619, Vol. 32, no 11, p. 2484-2495Article in journal (Refereed) Published
Abstract [en]

Growing evidence indicates that air pollution can negatively impact cognitive functions. The olfactory system is interesting in this context as it is directly exposed to pollutants and also associated with cognitive functions. The aim of this study was to investigate long- and short-term PM2.5 exposure in association with olfactory functions. Scores from odor tests were obtained from the Betula project - a longitudinal cohort study. Estimates of annual mean PM2.5 concentrations at the participants' residential address were obtained from a dispersion-model. Daily mean PM2.5 concentrations were obtained from a measuring station close to the test location. We found a positive association between long-term PM2.5 exposure and odor identification, i.e. exposure was associated with a better ability to identify odors. We also found an interaction effect between PM2.5 and age on odor identification. We found no associations between any PM2.5 exposure and odor detection or between short-term PM2.5 exposure and olfactory functions.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2022
Keywords
air pollution, olfaction
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:umu:diva-187140 (URN)10.1080/09603123.2021.1973969 (DOI)000691497900001 ()34461775 (PubMedID)2-s2.0-85113945507 (Scopus ID)
Funder
Swedish Research Council Formas, 942-2015-1099EU, Horizon 2020, H2020-MG-2018-2019-2020
Available from: 2021-09-03 Created: 2021-09-03 Last updated: 2023-02-23Bibliographically approved

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