Traffic-Related Air Pollution as a Risk Factor for Dementia: No Clear Modifying Effects of APOE ɛ4 in the Betula Cohort

Air pollution: a latent key driving force of dementia

Many researchers have studied the role of air pollutants on cognitive function, changes in brain structure, and occurrence of dementia. Due to the wide range of studies and often contradictory results, the present systematic review was conducted to try and clarify the relationship between air pollutants and dementia. To identify studies for this review, a systematic search was conducted in Scopus, PubMed, and Web of Science databases (without historical restrictions) until May 22, 2023. The PECO statement was created to clarify the research question, and articles that did not meet the criteria of this statement were excluded. In this review, animal studies, laboratory studies, books, review articles, conference papers and letters to the editors were avoided. Also, studies focused on the effect of air pollutants on cellular and biochemical changes (without investigating dementia) were also excluded. A quality assessment was done according to the type of design of each article, using the checklist developed by the Joanna Briggs Institute (JBI). Finally, selected studies were reviewed and discussed in terms of Alzheimer's dementia and non-Alzheimer's dementia. We identified 14,924 articles through a systematic search in databases, and after comprehensive reviews, 53 articles were found to be eligible for inclusion in the current systematic review. The results showed that chronic exposure to higher levels of air pollutants was associated with adverse effects on cognitive abilities and the presence of dementia. Studies strongly supported the negative effects of PM2.5 and then NO2 on the brain and the development of neurodegenerative disorders in old age. Because the onset of brain structural changes due to dementia begins decades before the onset of disease symptoms, and that exposure to air pollution is considered a modifiable risk factor, taking preventive measures to reduce air pollution and introducing behavioral interventions to reduce people's exposure to pollutants is advisable.

Joint Exposure to Multiple Air Pollutants, Genetic Susceptibility, and Incident Dementia: A Prospective Analysis in the UK Biobank Cohort

Objectives: This study aimed to evaluate the joint effects of multiple air pollutants including PM2.5, PM10, NO2, and NOx with dementia and examined the modifying effects of genetic susceptibility. Methods: This study included 220,963 UK Biobank participants without dementia at baseline. Weighted air pollution score reflecting the joint exposure to multiple air pollutants were constructed by cross-validation analyses, and inverse-variance weighted meta-analyses were performed to create a pooled effect. The modifying effect of genetic susceptibility on air pollution score was assessed by genetic risk score and APOE ε4 genotype. Results: The HR (95% CI) of dementia for per interquartile range increase of air pollution score was 1.13 (1.07∼1.18). Compared with the lowest quartile (Q1) of air pollution score, the HR (95% CI) of Q4 was 1.26 (1.13∼1.40) (P trend = 2.17 × 10-5). Participants with high air pollution score and high genetic susceptibility had higher risk of dementia compared to those with low air pollution score and low genetic susceptibility. Conclusion: Our study provides evidence that joint exposure to multiple air pollutants substantially increases the risk of dementia, especially among individuals with high genetic susceptibility.

Particulate Matter in Human Elderly: Higher Susceptibility to Cognitive Decline and Age-Related Diseases

This review highlights the significant impact of air quality, specifically particulate matter (PM), on cognitive decline and age-related diseases in the elderly. Despite established links to other pathologies, such as respiratory and cardiovascular illnesses, there is a pressing need for increased attention to the association between air pollution and cognitive aging, given the rising prevalence of neurocognitive disorders. PM sources are from diverse origins, including industrial activities and combustion engines, categorized into PM10, PM2.5, and ultrafine PM (UFPM), and emphasized health risks from both outdoor and indoor exposure. Long-term PM exposure, notably PM2.5, has correlated with declines in cognitive function, with a specific vulnerability observed in women. Recently, extracellular vesicles (EVs) have been explored due to the interplay between them, PM exposure, and human aging, highlighting the crucial role of EVs, especially exosomes, in mediating the complex relationship between PM exposure and chronic diseases, particularly neurological disorders. To sum up, we have compiled the pieces of evidence that show the potential contribution of PM exposure to cognitive aging and the role of EVs in mediating PM-induced cognitive impairment, which presents a promising avenue for future research and development of therapeutic strategies. Finally, this review emphasizes the need for policy changes and increased public awareness to mitigate air pollution, especially among vulnerable populations such as the elderly.

Association between late-life air pollution exposure and medial temporal lobe atrophy in older women

Background

Ambient air pollution exposures increase risk for Alzheimer's disease (AD) and related dementias, possibly due to structural changes in the medial temporal lobe (MTL). However, existing MRI studies examining exposure effects on the MTL were cross-sectional and focused on the hippocampus, yielding mixed results.

Method

To determine whether air pollution exposures were associated with MTL atrophy over time, we conducted a longitudinal study including 653 cognitively unimpaired community-dwelling older women from the Women's Health Initiative Memory Study with two MRI brain scans (MRI-1: 2005-6; MRI-2: 2009-10; Mage at MRI-1=77.3±3.5years). Using regionalized universal kriging models, exposures at residential locations were estimated as 3-year annual averages of fine particulate matter (PM2.5) and nitrogen dioxide (NO2) prior to MRI-1. Bilateral gray matter volumes of the hippocampus, amygdala, parahippocampal gyrus (PHG), and entorhinal cortex (ERC) were summed to operationalize the MTL. We used linear regressions to estimate exposure effects on 5-year volume changes in the MTL and its subregions, adjusting for intracranial volume, sociodemographic, lifestyle, and clinical characteristics.

Results

On average, MTL volume decreased by 0.53±1.00cm3 over 5 years. For each interquartile increase of PM2.5 (3.26μg/m3) and NO2 (6.77ppb), adjusted MTL volume had greater shrinkage by 0.32cm3 (95%CI=[-0.43, -0.21]) and 0.12cm3 (95%CI=[-0.22, -0.01]), respectively. The exposure effects did not differ by APOE ε4 genotype, sociodemographic, and cardiovascular risk factors, and remained among women with low-level PM2.5 exposure. Greater PHG atrophy was associated with higher PM2.5 (b=-0.24, 95%CI=[-0.29, -0.19]) and NO2 exposures (b=-0.09, 95%CI=[-0.14, -0.04]). Higher exposure to PM2.5 but not NO2 was also associated with greater ERC atrophy. Exposures were not associated with amygdala or hippocampal atrophy.

Conclusion

In summary, higher late-life PM2.5 and NO2 exposures were associated with greater MTL atrophy over time in cognitively unimpaired older women. The PHG and ERC - the MTL cortical subregions where AD neuropathologies likely begin, may be preferentially vulnerable to air pollution neurotoxicity.

Association of air pollution with dementia: a systematic review with meta-analysis including new cohort data from China

It remains unclear whether a total exposure to air pollution (AP) is associated with an increased risk of dementia. Little is known on the association in low- and middle-income countries. Two cohort studies in China (in Anhui cohort 1402 older adults aged ≥ 60 followed up for 10 years; in Zhejiang cohort 6115 older adults followed up for 5 years) were conducted to examine particulate matter - PM_2.5 associated with all dementia and air quality index (AQI) with Alzheimer's disease, respectively. A systematic literature review and meta-analysis was performed following worldwide literature searched until May 20, 2020 to identify 15 population-based cohort studies examining the association of AP with dementia (or any specific type of dementia) through PubMed, MEDLINE, PsycINFO, SocINDEX, CINHAL, and CNKI. The cohort studies in China showed a significantly increased relative risk (RR) of dementia in relation to AP exposure; in Anhui cohort the adjusted RR was 2.14 (95% CI 1.00-4.56) in people with PM_2.5 exposure at ≥ 64.5 μg/m³ versus <63.5 μg/m³ and in Zhejiang cohort the adjusted RR was 2.28 (1.07-4.87) in AQI>90 versus ≤ 80. The systematic review revealed that all 15 studies were undertaken in high income countries/regions, with inconsistent findings. While they had reasonably good overall quality of studies, seven studies did not adjust smoking in analysis and 13 did not account for depression. Pooling all eligible data demonstrated that dementia risk increased with the total AP exposure (1.13, 1.08-1.19). Data analysis of air pollutants showed that the RR significantly increased with PM_2.5 (1.06, 1.03-1.10 in 2nd tertile exposure; 1.13, 1.07-1.19 in 3rd tertile versus 1st tertile), PM₁₀ (1.05, 0.86-1.29; 1.62, 0.60-4.36), carbon monoxide (1.69, 0.72-3.93; 1.52, 1.35-1.71), nitrogen dioxide (1.06, 1.03-1.09; 1.18, 1.10-1.28) and nitrogen oxides (1.09, 1.04-1.15; 1.26, 1.13-1.41), but not ozone. Controlling air pollution and targeting on specific pollutants would reduce dementia globally.

Ambient air pollution and clinical dementia: systematic review and meta-analysis

OBJECTIVE

To investigate the role of air pollutants in risk of dementia, considering differences by study factors that could influence findings.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

EMBASE, PubMed, Web of Science, Psycinfo, and OVID Medline from database inception through July 2022.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies that included adults (≥18 years), a longitudinal follow-up, considered US Environmental Protection Agency criteria air pollutants and proxies of traffic pollution, averaged exposure over a year or more, and reported associations between ambient pollutants and clinical dementia. Two authors independently extracted data using a predefined data extraction form and assessed risk of bias using the Risk of Bias In Non-randomised Studies of Exposures (ROBINS-E) tool. A meta-analysis with Knapp-Hartung standard errors was done when at least three studies for a given pollutant used comparable approaches.

RESULTS

2080 records identified 51 studies for inclusion. Most studies were at high risk of bias, although in many cases bias was towards the null. 14 studies could be meta-analysed for particulate matter <2.5 µm in diameter (PM2.5). The overall hazard ratio per 2 μg/m3 PM2.5 was 1.04 (95% confidence interval 0.99 to 1.09). The hazard ratio among seven studies that used active case ascertainment was 1.42 (1.00 to 2.02) and among seven studies that used passive case ascertainment was 1.03 (0.98 to 1.07). The overall hazard ratio per 10 μg/m3 nitrogen dioxide was 1.02 ((0.98 to 1.06); nine studies) and per 10 μg/m3 nitrogen oxide was 1.05 ((0.98 to 1.13); five studies). Ozone had no clear association with dementia (hazard ratio per 5 μg/m3 was 1.00 (0.98 to 1.05); four studies).

CONCLUSION

PM2.5 might be a risk factor for dementia, as well as nitrogen dioxide and nitrogen oxide, although with more limited data. The meta-analysed hazard ratios are subject to limitations that require interpretation with caution. Outcome ascertainment approaches differ across studies and each exposure assessment approach likely is only a proxy for causally relevant exposure in relation to clinical dementia outcomes. Studies that evaluate critical periods of exposure and pollutants other than PM2.5, and studies that actively assess all participants for outcomes are needed. Nonetheless, our results can provide current best estimates for use in burden of disease and regulatory setting efforts.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42021277083.

Global incidence of young-onset dementia: A systematic review and meta-analysis

INTRODUCTION

Reliable data on the incidence rates for young-onset dementia (YOD) are lacking, but are necessary for research on disease etiology and to raise awareness among health care professionals.

METHODS

We performed a systematic review and meta-analysis on population-based studies on the incidence of YOD, published between January 1, 1990 and February 1, 2022, according to Meta-analyses of Observational Studies in Epidemiology (MOOSE) guidelines. Data were analyzed using random-effects meta-analyses. Results were age-standardized, and heterogeneity was assessed by subgroup analyses and meta-regression.

RESULTS

Sixty-one articles were included. Global age-standardized incidence rates increased from 0.17/100,000 in age 30 to 34 years, to 5.14/100,000 in age 60 to 64 years, giving a global total age-standardized incidence rate of 11 per 100,000 in age 30 to 64. This corresponds to 370,000 new YOD cases annually worldwide. Heterogeneity was high and meta-regression showed geographic location significantly influenced this heterogeneity.

DISCUSSION

This meta-analysis shows the current best estimate of YOD incidence. New prospective cohort studies are needed.

PM2.5 and Dementia in a Low Exposure Setting: The Influence of Odor Identification Ability and APOE

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 ɛ4 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 6.77μg/m3, which is 1.77μg/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 1μg/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 (ɛ4 carriers versus non-carriers), and odor identification ability (high versus low), showed associations only for ɛ4 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.

Associations of Air Pollution and Genetic Risk With Incident Dementia: A Prospective Cohort Study

Evidence on the association between air pollution and dementia is accumulating but still inconclusive, and the potential effect modification by genetics is unclear. We investigated the joint effects of air pollution exposure and genetic risk on incident dementia in a prospective cohort study, the UK Biobank study. Land use regression models were used to estimate exposure to ambient particulate matter (PM) in 3 fraction sizes (PM with diameter < 2.5 μm (PM2.5), coarse particles (PM with diameter 2.5-10 μm (PMc)), and PM with diameter < 10 μm (PM10)), PM2.5 absorbance, nitrogen dioxide levels, and nitrogen oxide levels at each individual's baseline residence. A polygenic risk score was calculated as a quantitative measure of genetic dementia risk. Incident cases of dementia were ascertained through linkage to health administrative data sets. Among the 227,840 participants included in the analysis, 3,774 incident dementia cases (including 1,238 cases of Alzheimer disease and 563 cases of vascular dementia) were identified. After adjustment for a variety of covariates, including genetic factors, positive associations were found between exposure to air pollution-particularly PM10, PM2.5 absorbance, and nitrogen dioxide-and incident all-cause dementia and Alzheimer disease but not vascular dementia. No significant interaction between air pollution and genetics was found, either on the multiplicative scale or on the additive scale. Exposure to air pollution was associated with a higher risk of developing dementia regardless of genetic risk.

Air Pollution and Incidence of Dementia: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

Studies of association between air pollution and incidence of dementia have shown discrepant results. The aim of this study was to evaluate the association between air pollution and dementia.

METHODS

In this systematic review and meta-analysis, PubMed, MEDLINE, EMBASE, PsycINFO, Scopus, and Web of Science were searched and updated in August 2021. Population-based cohort studies that reported on hazard ratio (HR) of dementia in association with exposure to fine particulate matter (PM_2·5), nitrogen oxides (NO_X), nitrogen dioxide (NO₂), or ozone (O₃) in those aged >40 years were included. Data were extracted by 2 independent investigators. The main outcome was the pooled HR for dementia per increment of pollutant, calculated using a random-effects model. Results were reported in accordance with PRISMA guidelines. The protocol was registered in PROSPERO (registration number: CRD42020219036).

RESULTS

A total of 20 studies were included in the systematic review, and 17 provided data for the meta-analysis. The total included population was 91,391,296, with 5,521,111 (6%) being diagnosed with dementia. A total of 12, 5, 6, and 4 studies were included in the meta-analyses of PM_2·5, NO_X, NO₂, and O₃, respectively. The risk of dementia increased by 3% per 1 μg/m³ increment in PM_2·5 (HR, 1.03; 95% CI [1.02-1.05]; I² = 100%). The association between dementia per 10 μg/m³ increment in NO_X (HR, 1.05; 95% CI [0.99-1.13]; I² = 61%), NO₂ (HR, 1.03; 95% CI [1.00-1.07]; I² = 94%), and O₃ levels (HR, 1.01; 95% CI [0.91-1.11]; I² = 82%) was less clear, although a significant association could not be ruled out, and there was high heterogeneity across studies.

DISCUSSION

Existing evidence suggests a significant association between exposure to PM_2·5 and incidence of dementia and nonsignificant association between dementia and NO_X, NO₂, and O₃ exposure. However, results should be interpreted in light of the small number of studies and high heterogeneity of effects across studies.

Air pollution exposure during pregnancy and childhood, APOE ε4 status and Alzheimer polygenic risk score, and brain structural morphology in preadolescents

BACKGROUND

Air pollution exposure is associated with impaired neurodevelopment, altered structural brain morphology in children, and neurodegenerative disorders. Differential susceptibility to air pollution may be influenced by genetic features.

OBJECTIVES

To evaluate whether the apolipoprotein E (APOE) genotype or the polygenic risk score (PRS) for Alzheimer's Disease (AD) modify the association between air pollution exposure during pregnancy and childhood and structural brain morphology in preadolescents.

METHODS

We included 1186 children from the Generation R Study. Concentrations of fourteen air pollutants were calculated at participants' home addresses during pregnancy and childhood using land-use-regression models. Structural brain images were collected at age 9-12 years to assess cortical and subcortical brain volumes. APOE status and PRS for AD were examined as genetic modifiers. Linear regression models were used to conduct single-pollutant and multi-pollutant (using the Deletion/Substitution/Addition algorithm) analyses with a two-way interaction between air pollution and each genetic modifier.

RESULTS

Higher pregnancy coarse particulate matter (PM_coarse) and childhood polycyclic aromatic hydrocarbons exposure was differentially associated with larger cerebral white matter volume in APOE ε4 carriers compared to non-carriers (29,485 mm³ (95% CI 6,189; 52,781) and 18,663 mm³ (469; 36,856), respectively). Higher pregnancy PM_coarse exposure was differentially associated with larger cortical grey matter volume in children with higher compared to lower PRS for AD (19436 mm³ (825, 38,046)).

DISCUSSION

APOE status and PRS for AD possibly modify the association between air pollution exposure and brain structural morphology in preadolescents. Higher air pollution exposure is associated with larger cortical volumes in APOE ε4 carriers and children with a high PRS for AD. This is in line with typical brain development, suggesting an antagonistic pleiotropic effect of these genetic features (i.e., protective effect in early-life, but neurodegenerative effect in adulthood). However, we cannot discard chance findings. Future studies should evaluate trajectorial brain development using a longitudinal design.

Associations Between Ambient Air Pollution and Cognitive Abilities from Midlife to Early Old Age: Modification by APOE Genotype

BACKGROUND

Fine particulate matter (PM2.5) and nitrogen dioxide (NO2) measures of ambient air pollution are associated with accelerated age-related cognitive impairment, and Alzheimer's disease and related dementias (ADRD).

OBJECTIVE

We examined associations between air pollution, four cognitive factors, and the moderating role of apolipoprotein E (APOE) genotype in the understudied period of midlife.

METHODS

Participants were ∼1,100 men in the Vietnam Era Twin Study of Aging. Baseline cognitive assessments were from 2003 to 2007. Measures included past (1993-1999) and recent (3 years prior to baseline assessment) PM2.5 and NO2 exposure, in-person assessment of episodic memory, executive function, verbal fluency, and processing speed, and APOE genotype. Average baseline age was 56 years with a 12-year follow-up. Analyses adjusted for health and lifestyle covariates.

RESULTS

Performance in all cognitive domains declined from age 56 to 68. Higher PM2.5 exposures were associated with worse general verbal fluency. We found significant exposure-by-APOE genotype interactions for specific cognitive domains: PM2.5 with executive function and NO2 with episodic memory. Higher PM2.5 exposure was related to worse executive function in APOE ɛ4 carriers, but not in non-carriers. There were no associations with processing speed.

CONCLUSION

These results indicate negative effects of ambient air pollution exposure on fluency alongside intriguing differential modifications of cognitive performance by APOE genotype. APOE ɛ4 carriers appeared more sensitive to environmental differences. The process by which air pollution and its interaction with genetic risk for ADRD affects risk for later life cognitive decline or progression to dementia may begin in midlife.

Urinary polycyclic aromatic hydrocarbon metabolites, plasma p-tau231 and mild cognitive impairment in coke oven workers

BACKGROUND

As a group of environmental pollutants, polycyclic aromatic hydrocarbons (PAHs) may be neurotoxic，especially in high-exposure occupational populations. However, the effect of PAHs on mild cognitive impairment (MCI) is still unclear.

OBJECTIVE

We aimed to investigate the relationship between PAH metabolites and MCI and to explore whether plasma p-tau231 can be used as a potential biomarker to reflect MCI in coke oven workers.

METHOD

A total of 330 workers were recruited from a coke oven plant as the exposure group, and 234 workers were recruited from a water treatment plant as the control group. The concentrations of eleven PAH metabolites and plasma p-tau231 were determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) and ELISA. Cognitive function was measured by the Montreal Cognitive Assessment (MoCA) questionnaire. A multivariate logistic regression model and multiple linear regression model were used to analyze the associations of urinary PAH metabolites with the detection rate of MCI, MoCA scores and plasma p-tau231. The dose-response relationships were evaluated using restricted cubic spline models.

RESULTS

We found 146 MCI-positive workers in coke oven plant (44.24%), and 69 MCI-positive workers in water treatment plant (29.49%). In addition, the urinary sum of PAH metabolites (Ʃ-OH PAHs) was significantly associated with MCI (OR, 1.371; 95% CI:1.102-1.705). Each one-unit increase in ln-transformed Ʃ-OH PAHs was associated with a 0.429 decrease in the sum of MoCA, a 0.281 reduction in the visuospatial/executive function and a 9.416 increase in the level of plasma P-Tau231. We found a negative association between plasma P-Tau231 and visuospatial/executive function (β = -0.007, 95% CI: -0.011, -0.003).

CONCLUSION

Our data indicated that urinary Ʃ-OH PAHs levels of workers were positively associated with MCI and the level of plasma P-Tau231.

Long-term exposure to low-level air pollution, genetic susceptibility and risk of dementia

BACKGROUND

We aimed to assess the association between low-level air pollution and the risk of dementia, and examine the modification effect by genetic susceptibility on the relationship.

METHODS

A total of 164 447 participants who were free of dementia at baseline and aged ≥60 years were included. Annual average concentrations of particulate matter (PM) with diameters of ≤2.5 μm (PM2.5), between 2.5 and 10 μm (PMcoarse), PM2.5 absorbance and nitrogen dioxides (NO2) were evaluated using the Land Use Regression models. Cox proportional hazards regression was used to estimate the association between air pollutants and incident dementia.

RESULTS

The adjusted hazard ratio (HR) of dementia for a 5-μg/m3 increase in NO2 was 1.09 (95% CI, 1.05-1.14); the adjusted HR of dementia for a 1-μg/m3 increase in PM2.5 was 1.10 (1.04-1.17). Such significant associations were present even within concentration ranges well below the present World Health Organization, US and European annual mean limit values. In addition, higher PM2.5 absorbance, a marker closely related to motorized traffic, was associated with higher risk of dementia. We found the risk of dementia associated with a combination of air pollutants (NO2 or PM2.5) and high genetic susceptibility (APOE-ε4 alleles or overall genetic susceptibility) was greater than the addition of the risk associated with each individual factor, indicating significant interactions on an additive scale (all P-interaction < 0.05).

CONCLUSION

Long-term exposure to PM2.5 or NO2, even at relatively low levels, is associated with a higher risk of dementia. Air pollution may additively interact with the genetic susceptibility on dementia risk.

Exposure to air pollution and risk of incident dementia in the UK Biobank

BACKGROUND

Air pollution may cause inflammatory and oxidative stress damage to the brain, leading to neurodegenerative disease. The association between air pollution and dementia, and modification by apolipoprotein E genotype 4 (APOE-ε4) has yet to be fully investigated.

OBJECTIVES

To examine associations of air pollution with three types of incident dementias (Alzheimer's disease (AD), frontotemporal dementia (FTD), and vascular dementia (VAD)), and their potential modification by APOE-ε4 genotype.

METHODS

The UK Biobank enrolled >500,000 participants (2006-2010) with ongoing follow-up. We used annual averages of air pollution (PM_2.5, PM₁₀, PM_2.5-10, PM_{2.5absorbance}, NO₂, NO_X) for 2010 scaled to interquartile ranges (IQR). We included individuals aged ≥60 years, with no dementia diagnosis prior to January 1, 2010. Time to incident dementia and follow-up time were reported from baseline (January 01, 2010) to last censor event (death, last hospitalization, or loss to follow-up). Cox proportional hazard ratios (HR) and 95% confidence intervals (95% CI) were calculated to estimate the association of air pollutants and incident dementia, and modification of these associations by APOE-ε4.

RESULTS

Our sample included 187,194 individuals (including N = 680 AD, N = 377 VAD, N = 63 FTD) with a mean follow-up of 7.04 years. We observed consistent associations of PM_2.5 with greater risk of all-cause dementia (HR = 1.17, 95% CI: 1.10, 1.24) and AD (HR = 1.17, 95% CI: 1.06, 1.29). NO₂ was also associated with greater risk of any incident dementia (HR = 1.18, 95% CI: 1.10, 1.25), AD (HR = 1.15, 95% CI: 1.04, 1.28) and VAD (HR = 1.18, 95% CI: 1.03, 1.35). APOE-ε4 did not modify the association between any air pollutants and dementia.

DISCUSSION

PM_2.5 and NO₂ levels were associated with several types of dementia, and these associations were not modified by APOE-ε4. Findings from the UK Biobank support and extend to other epidemiological evidence for the potential association of air pollutants with detrimental brain health during aging.

Association of Long-term Exposure to Ambient Air Pollution With Cognitive Decline and Alzheimer's Disease-Related Amyloidosis

BACKGROUND

Air pollution induces neurotoxic reactions and may exert adverse effects on cognitive health. We aimed to investigate whether air pollutants accelerate cognitive decline and affect neurobiological signatures of Alzheimer's disease (AD).

METHODS

We used a population-based cohort from the Chinese Longitudinal Healthy Longevity Survey with 31,573 participants and a 10-year follow-up (5878 cognitively unimpaired individuals in Chinese Longitudinal Healthy Longevity Survey followed for 5.95 ± 2.87 years), and biomarker-based data from the Chinese Alzheimer's Biomarker and Lifestyle study including 1131 participants who underwent cerebrospinal fluid measurements of AD-related amyloid-β (Aβ) and tau proteins. Cognitive impairment was determined by education-corrected performance on the China-Modified Mini-Mental State Examination. Annual exposures to fine particulate matter (PM_2.5), ground-level ozone (O₃), and nitrogen dioxide (NO₂) were estimated at areas of residence. Exposures were aggregated as 2-year averages preceding enrollments using Cox proportional hazards or linear models.

RESULTS

Long-term exposure to PM_2.5 (per 20 μg/m³) increased the risk of cognitive impairment (hazard ratio, 1.100; 95% CI: 1.026-1.180), and similar associations were observed from separate cross-sectional analyses. Exposures to O₃ and NO₂ yielded elevated risk but with nonsignificant estimates. Individuals exposed to high PM_2.5 manifested increased amyloid burdens as reflected by cerebrospinal fluid-AD biomarkers. Moreover, PM_2.5 exposure-associated decline in global cognition was partly explained by amyloid pathology as measured by cerebrospinal fluid-Aβ₄₂/Aβ₄₀, P-tau/Aβ₄₂, and T-tau/Aβ₄₂, with mediation proportions ranging from 16.95% to 21.64%.

CONCLUSIONS

Long-term exposure to PM_2.5 contributed to the development of cognitive decline, which may be partly explained by brain amyloid accumulation indicative of increased AD risk.

Impact of air pollution exposure on the risk of Alzheimer's disease in China: A community-based cohort study

Alzheimer's disease (AD) is the most common type of dementia. Impact of air pollution (AP) on the risk of AD is unclear. It is unknown which air pollutants are independently associated with AD and whether fish consumption mitigated the association. We carried out a community-based cohort of 6115 participants aged ≥60 years in China to examine the association of PM_2.5, PM₁₀, CO, NO₂, SO₂ and O₃ exposure with AD, and differences in the association between people with low and high consumption of fish. The participants were randomly recruited from six counties in Zhejiang province for health survey to document socio-demographic and disease risk factors in 2014, and were followed up to diagnose AD in 2019. A total of 986 cohort members were diagnosed with AD. Based on the daily mean air pollutants monitored in 2013-2015 in the counties, participants were divided into low, middle and high AP exposure groups for subsequent analysis. The multiple adjusted odds ratio (OR) of AD in participants living with the middle and high levels of PM_2.5 exposure versus the low exposure were 1.50 (95% CI 0.90-2.50) and 3.92 (2.09-7.37). The increased ORs were also with PM₁₀ (1.74, 0.65-4.64; 3.00, 1.22-7.41) and CO (2.86, 1.32-6.20; 1.19, 0.45-3.18), but not with NO₂ (0.63, 0.17-2.27; 0.95, 0.28-3.19), SO₂ (0.44, 0.19-1.001; 1.21, 0.56-2.62), and O₃ (0.38, 0.20-0.74; 0.50, 0.21-1.21). There were no significant interaction effects of AP with fish consumption on AD. However, participants with low consumption of fish appeared to have higher ORs in PM_2.5 exposure (1.80, 1.39-2.33; 5.18, 3.93-6.82) than those high consumption (1.38, 0.78-2.47; 2.89, 1.50-5.59). Our findings of PM_2.5, PM₁₀ and CO exposure significantly increased the risk of AD and the potential mitigating effect of fish consumption on the association provide evidence for developing effective strategies for AD reduction and air pollution control.

Effects of air pollution on dementia over Europe for present and future climate change scenarios

The scientific literature is scarce when referring to the influence of atmospheric pollutants on neurodegenerative diseases for present and future climate change scenarios. In this sense, this contribution evaluates the incidence of dementia (Alzheimer's disease, AD, and dementia from unspecified cause, DU) occurring in Europe associated with the exposure to air pollution (essentially NO₂ and PM2.5) for the present climatic period (1991-2010) and for a future climate change scenario (RCP8.5, 2031-2050). The GEMM methodology has been applied to air pollution simulations using the chemistry/climate regional model WRF-Chem. Present population data were obtained from NASA's Center for Socioeconomic Data and Applications (SEDAC); while future population projections for the year 2050 were derived from the United Nations (UN) Department of Economic and Social Affairs-Population Dynamics. Overall, the estimated incidence rate (cases per year) of AD and DU associated with exposure to air pollution over Europe is 498,000 [95% confidence interval (95% CI) 348,600-647,400] and 314,000 (95% CI 257,500-401,900), respectively. An important increase in the future incidence rate is projected (around 72% for both types of dementia) when considering the effect of climate change together with the foreseen changes in the future population, because of the expected aging of European population. The climate penalty (impacts of future climate change alone on air quality) has a limited effect on the total changes of dementia (approx. 0.5%), because the large increase in the incidence rate over southern Europe is offset by its decrease over more northern countries, favored by an improvement of air pollution caused by the projected enhancement of rainfall.

Neurovascular Alterations in Vascular Dementia: Emphasis on Risk Factors

Vascular dementia (VaD) constitutes the second most prevalent cause of dementia in the world after Alzheimer’s disease (AD). VaD regroups heterogeneous neurological conditions in which the decline of cognitive functions, including executive functions, is associated with structural and functional alterations in the cerebral vasculature. Among these cerebrovascular disorders, major stroke, and cerebral small vessel disease (cSVD) constitute the major risk factors for VaD. These conditions alter neurovascular functions leading to blood-brain barrier (BBB) deregulation, neurovascular coupling dysfunction, and inflammation. Accumulation of neurovascular impairments over time underlies the cognitive function decline associated with VaD. Furthermore, several vascular risk factors, such as hypertension, obesity, and diabetes have been shown to exacerbate neurovascular impairments and thus increase VaD prevalence. Importantly, air pollution constitutes an underestimated risk factor that triggers vascular dysfunction via inflammation and oxidative stress. The review summarizes the current knowledge related to the pathological mechanisms linking neurovascular impairments associated with stroke, cSVD, and vascular risk factors with a particular emphasis on air pollution, to VaD etiology and progression. Furthermore, the review discusses the major challenges to fully elucidate the pathobiology of VaD, as well as research directions to outline new therapeutic interventions.

Local Contrasts in Concentration of Ambient Particulate Air Pollution (PM2.5) and Incidence of Alzheimer's Disease and Dementia: Results from the Betula Cohort in Northern Sweden

Exposure to fine particulate air pollution (PM2.5) is emerging as a risk factor for Alzheimer's disease (AD), but existing studies are still limited and heterogeneous. We have previously studied the association between dementia (AD and vascular dementia) and PM2.5 stemming from vehicle exhaust and wood-smoke in the Betula cohort in Northern Sweden. The aim of this commentary is to estimate the association between total PM2.5 and dementia in the Betula cohort, which is more relevant to include in future meta-estimates than the source-specific estimates. The hazard ratio for incident dementia associated with a 1μg/m3 increase in local PM2.5 was 1.38 (95% confidence interval: 0.99 -1.92). The interpretation of our results is that they indicate an association between local contrasts in concentration of PM2.5 at the residential address and incidence of dementia in a low-level setting.

Ozone and Particulate Matter Exposure and Alzheimer's Disease: A Review of Human and Animal Studies

Alzheimer's disease (AD), an aging-related neurodegenerative disease, is a major cause of dementia in the elderly. Although the early-onset (familial) AD is attributed to mutations in the genes coding for amyloid-β protein precursor (AβPP) and presenilin1/presenilin 2 (PS1/PS2), the cause for the late-onset AD (LOAD), which accounts for more than 95% of AD cases, remains unclear. Aging is the greatest risk factor for LOAD, whereas the apolipo protein E4 allele (APOEɛ4) is believed to be a major genetic risk factor in acquiring LOAD, with female APOEɛ4 carriers at highest risk. Nonetheless, not all the elderly, even older female APOEɛ4 carriers, develop LOAD, suggesting that other factors, including environmental exposure, must play a role. This review summarizes recent studies that show a potential role of environmental exposure, especially ozone and particulate matter exposure, in the development of AD. Interactions between environmental exposure, genetic risk factor (APOEɛ4), and sex in AD pathophysiology are also discussed briefly. Identification of environmental risk factor(s) and elucidation of the complex interactions between genetic and environmental risk factors plus aging and female sex in the onset of AD will be a key to our understanding of the etiology and pathogenesis of AD and the development of the strategies for its prevention and treatment.

A critical review of the epidemiological evidence of effects of air pollution on dementia, cognitive function and cognitive decline in adult population

Dementia is arguably the most pressing public health challenge of our age. Since dementia does not have a cure, identifying risk factors that can be controlled has become paramount to reduce the personal, societal and economic burden of dementia. The relationship between exposure to air pollution and effects on cognitive function, cognitive decline and dementia has stimulated increasing scientific interest in the past few years. This review of the literature critically examines the available epidemiological evidence of associations between exposure to ambient air pollutants, cognitive performance, acceleration of cognitive decline, risk of developing dementia, neuroimaging and neurological biomarker studies, following Bradford Hill guidelines for causality. The evidence reviewed has been consistent in reporting associations between chronic exposure to air pollution and reduced global cognition, as well as impairment in specific cognitive domains including visuo-spatial abilities. Cognitive decline and dementia incidence have also been consistently associated with exposure to air pollution. The neuro-imaging studies reviewed report associations between exposure to air pollution and white matter volume reduction. Other reported effects include reduction in gray matter, larger ventricular volume, and smaller corpus callosum. Findings relating to ischemic (white matter hyperintensities/silent cerebral infarcts) and hemorrhagic (cerebral microbleeds) markers of cerebral small vessel disease have been heterogeneous, as have observations on hippocampal volume and air pollution. The few studies available on neuro-inflammation tend to report associations with exposure to air pollution. Several effect modifiers have been suggested in the literature, but more replication studies are required. Traditional confounding factors have been controlled or adjusted for in most of the reviewed studies. Additional confounding factors have also been considered, but the inclusion of these has varied among the different studies. Despite all the efforts to adjust for confounding factors, residual confounding cannot be completely ruled out, especially since the factors affecting cognition and dementia are not yet fully understood. The available evidence meets many of the Bradford Hill guidelines for causality. The reported associations between a range of air pollutants and effects on cognitive function in older people, including the acceleration of cognitive decline and the induction of dementia, are likely to be causal in nature. However, the diversity of study designs, air pollutants and endpoints examined precludes the attribution of these adverse effects to a single class of pollutant and makes meta-analysis inappropriate.

Long-Term Exposure to PM2.5 and Cognitive Decline: A Longitudinal Population-Based Study

BACKGROUND

A growing but contrasting evidence relates air pollution to cognitive decline. The role of cerebrovascular diseases in amplifying this risk is unclear.

OBJECTIVES

1) Investigate the association between long-term exposure to air pollution and cognitive decline; 2) Test whether cerebrovascular diseases amplify this association.

METHODS

We examined 2,253 participants of the Swedish National study on Aging and Care in Kungsholmen (SNAC-K). One major air pollutant (particulate matter ≤2.5μm, PM2.5) was assessed yearly from 1990, using dispersion models for outdoor levels at residential addresses. The speed of cognitive decline (Mini-Mental State Examination, MMSE) was estimated as the rate of MMSE decline (linear mixed models) and further dichotomized into the upper (25%fastest cognitive decline), versus the three lower quartiles. The cognitive scores were used to calculate the odds of fast cognitive decline per levels of PM2.5 using regression models and considering linear and restricted cubic splines of 10 years exposure before the baseline. The potential modifier effect of cerebrovascular diseases was tested by adding an interaction term in the model.

RESULTS

We observed an inverted U-shape relationship between PM2.5 and cognitive decline. The multi-adjusted piecewise regression model showed an increased OR of fast cognitive decline of 81%(95%CI = 1.2-3.2) per interquartile range difference up to mean PM2.5 level (8.6μg/m3) for individuals older than 80. Above such level we observed no further risk increase (OR = 0.89;95%CI = 0.74-1.06). The presence of cerebrovascular diseases further increased such risk by 6%.

CONCLUSION

Low to mean PM2.5 levels were associated with higher risk of accelerated cognitive decline. Cerebrovascular diseases further amplified such risk.

The Role of Traffic-Related Air Pollution on Neurodegenerative Diseases in Older People: An Epidemiological Perspective

Traffic-related air pollution is ubiquitous and almost impossible to avoid. It is important to understand the role that traffic-related air pollution may play in neurodegenerative diseases, such as dementia, Alzheimer's disease, and Parkinson's disease, particularly among older populations and at-risk groups. There is a growing interest in this area among the environmental epidemiology literature and the body of evidence identifying this role is emerging and strengthening. This review focuses on the principal components of traffic-related air pollutants (particulate matter and nitrogen oxides) and the epidemiological evidence of their contribution to common neurodegenerative diseases. All studies reported are currently observational in nature and there are mixed findings depending on the study design, assessment of traffic-related air pollutant levels, assessment of the neurodegenerative disease outcome, time period of assessment, and the role of confounding environmental factors and at-risk genetic characteristics. All current studies have been conducted in income-rich countries where traffic-related air pollution levels are relatively low. Additional longer-term studies are needed to confirm the levels of risk, consider other contributing environmental factors and to be conducted in settings where air pollution exposures are higher and at-risk populations reside and work. Better understanding of these relationships will help inform the development of preventive measures and reduce chronic cognitive and physical health burdens (cost, quality of life) at personal and societal levels.

Exposure to Traffic-Generated Pollutants Exacerbates the Expression of Factors Associated with the Pathophysiology of Alzheimer’s Disease in Aged C57BL/6 Wild-Type Mice

Background: Multiple studies report a strong correlation between traffic-generated air pollution-exposure and detrimental outcomes in the central nervous system (CNS), including Alzheimer’s disease (AD). Incidence of AD is rapidly increasing and, worldwide, many live in regions where pollutants exceed regulatory standards. Thus, it is imperative to identify environmental pollutants that contribute to AD, and the mechanisms involved. Objective: We investigated the effects of mixed gasoline and diesel engine emissions (MVE) on the expression of factors involved in progression of AD in the hippocampus and cerebrum in a young versus aged mouse model. Methods: Young (2 months old) and aged (18 months old) male C57BL/6 mice were exposed to either MVE (300μg/m3 PM) or filtered air (FA) for 6 h/d, 7 d/wk, for 50 d. Immunofluorescence and RT-qPCR were used to quantify oxidative stress (8-OHdG) and expression of amyloid-β protein precursor (AβPP), β secretase (BACE1), amyloid-β (Aβ), aryl hydrocarbon receptor (AhR), cytochrome P450 (CYP) 1B1, angiotensin-converting enzyme (ACE1), and angiotensin II type 1 (AT1) receptor in the cerebrum and hippocampus, in addition to cerebral microvascular tight junction (TJ) protein expression. Results: We observed age-related increases in oxidative stress, AhR, CYP1B1, Aβ, BACE1, and AT1 receptor in the CA1 region of the hippocampus, and elevation of cerebral AβPP, AhR, and CYP1B1 mRNA, associated with decreased cerebral microvascular TJ protein claudin-5. MVE-exposure resulted in further promotion of oxidative stress, and significant increases in AhR, CYP1B1, BACE1, ACE1, and Aβ, compared to the young and aged FA-exposed mice. Conclusion: Such findings suggest that MVE-exposure exacerbates the expression of factors in the CNS associated with AD pathogenesis in aged populations.

Biological and environmental predictors of heterogeneity in neurocognitive ageing: Evidence from Betula and other longitudinal studies

Individual differences in cognitive performance increase with advancing age, reflecting marked cognitive changes in some individuals along with little or no change in others. Genetic and lifestyle factors are assumed to influence cognitive performance in ageing by affecting the magnitude and extent of age-related brain changes (i.e., brain maintenance or atrophy), as well as the ability to recruit compensatory processes. The purpose of this review is to present findings from the Betula study and other longitudinal studies, with a focus on clarifying the role of key biological and environmental factors assumed to underlie individual differences in brain and cognitive ageing. We discuss the vital importance of sampling, analytic methods, consideration of non-ignorable dropout, and related issues for valid conclusions on factors that influence healthy neurocognitive ageing.

Ambient Air Pollution Increases the Risk of Cerebrovascular and Neuropsychiatric Disorders through Induction of Inflammation and Oxidative Stress

Exposure to ambient air pollution is a well-established determinant of health and disease. The Lancet Commission on pollution and health concludes that air pollution is the leading environmental cause of global disease and premature death. Indeed, there is a growing body of evidence that links air pollution not only to adverse cardiorespiratory effects but also to increased risk of cerebrovascular and neuropsychiatric disorders. Despite being a relatively new area of investigation, overall, there is mounting recent evidence showing that exposure to multiple air pollutants, in particular to fine particles, may affect the central nervous system (CNS) and brain health, thereby contributing to increased risk of stroke, dementia, Parkinson's disease, cognitive dysfunction, neurodevelopmental disorders, depression and other related conditions. The underlying molecular mechanisms of susceptibility and disease remain largely elusive. However, emerging evidence suggests inflammation and oxidative stress to be crucial factors in the pathogenesis of air pollution-induced disorders, driven by the enhanced production of proinflammatory mediators and reactive oxygen species in response to exposure to various air pollutants. From a public health perspective, mitigation measures are urgent to reduce the burden of disease and premature mortality from ambient air pollution.