Alzheimer's disease-like cortical atrophy mediates the effect of air pollution on global cognitive function

What are the consequences of PM air pollution exposure on elderly behavior? A systematic review

Environmental pollution poses a significant risk to human health. Particulate matter (PM) found in polluted air is particularly of concern due to its ability to penetrate the blood-brain barrier (BBB) and impact the central nervous system (CNS), affecting sensory, cognitive, and emotional well-being. The aim of this review is to provide a comprehensive overview on the latest evidence regarding the association between PM exposure and behavioral outcomes in adult and older populations. Searches were conducted across PubMed, Web of Science, and Scopus up to August 2023, with articles selected and screened following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 27 articles meeting the criteria were included, and their risk of bias was evaluated using the Newcastle Ottawa Scale. The studies primarily focused on PM2.5 and PM10 in regions such as Europe, the USA, and Asia. While data on the impact of PM exposure on sensory variables were limited, suggesting an adverse effect, overall findings indicated a link between PM exposure and worsened cognitive function, increased risk of dementia, depressive symptoms, and anxiety. Some studies highlighted sex-dependent effects of PM exposure, with women experiencing a higher prevalence of adverse effects. This review underscores the importance of further research to understand the specific cognitive aspects affected by PM exposure, particularly in relation to dementia risk.

Role of air pollution exposure in the alteration of brain cortical structure: A Mendelian randomization study

BACKGROUND

Accumulating research has linked ambient air pollution exposure to alterations in cortical surface area (SA) and thickness; however, the causal inferences remain controversial. Our investigation aims to determine the causality between air pollution and brain cortical morphology using the Mendelian randomization (MR) approach.

METHODS

Public accessible genome-wide association studies data on particulate matter 2.5 (PM2.5), PM2.5 absorbance, PM10, PM2.5-10, nitrogen dioxide (NO2), and nitrogen oxides (NOX) concentration were screened to select instrumental variables. Univariable MR (UVMR) was performed to assess the causality of air pollution on brain cortical structure using five MR methods. Multivariable MR (MVMR) was further conducted to strengthen the robustness of the identified relationships by adjusting for related pollutant phenotypes, household income, and unhealthy eating habits.

RESULTS

The UVMR analysis identified fourteen causal associations between air pollution susceptibility and alterations in brain cortical morphology, with nine showing negative effects and five showing positive effects concurrently. The MVMR models indicated negative causal relationships between PM2.5 level and the SA of the inferior temporal cortex (beta [95 %CI] = -215.739 [-404.284 to -27.194], p = 0.025), NO2 level and the SA of the lateral occipital cortex (beta [95 %CI] = -548.577 [-1086.450 to -10.699], p = 0.046), and a positive correlation between PM2.5 absorbance and SA of the bankssts cortex (beta [95 %CI] = 76.491 [14.267-138.716], p = 0.016). No evidence of heterogeneity or pleiotropy was noticed.

CONCLUSIONS

Our exploration established causal relationships between air pollution exposure and brain cortical structure, underscoring the significance of mitigating air pollution to preserve brain cortical morphology.

Psychological repercussions of PM air pollution in human aging: a comprehensive review of urban and rural environments

Air pollution and its effects on population health are currently among the most important public health issues. It is well established that the impact of air pollution on health is exceedingly high, although it ignores its real scope and effects on the aging process because studies on air quality have largely focused on younger age groups. Herein, we emphasize the relevance of air quality to the behavioral aging process, taking into account the place of residence - rural or urban. We raise the following question: Can air quality and residential settings modulate cognitive, emotional and social behaviors during the aging? Some studies have analyzed the role of residential settings and air pollution in the context of a behavioral frame in elderly people. Based on the analyzed literature, this revision concluded that air pollutants affect cognitive function, increasing the risk of dementia as well as depression and anxiety emotional responses. In addition, social networks and inclusion can modulate and mitigate the effects observed during the aging in rural areas that are exposed to less contamination. Although there is no consensus, it seems that some observed behavioral effects are sex-dependent, as women are more vulnerable to air pollution. Additionally, we examined why older adults are vulnerable to the health effects of Particulate Matter (PM) exposure and highlighted the importance of social health in this context. Environmental agents could be the key to understanding the susceptibility and variability observed during aging in behavioral symptoms. Although cognitive decline is related to increased age, it is not a manipulated factor. Efforts should be centered on locating factors implicated in the aging process that could be susceptible to manipulation or variation, such as the choice of the place of residence and the air that we are breathing. Given the significant societal impact of PM, research and policy regulations should be closely aligned and collaborative.

Cognitive benefits of fine particle health-protective behaviors in older adults

This study aimed to analyze the relationship between health-protective behaviors against fine particle exposure and cognitive function among the elderly. A total of 100 individuals aged 60 and above at a dementia relief center in a specific district participated in this study. Cognitive function was examined using the Cognitive Screening Test (CIST). Descriptive analysis, t-tests, cross-tabulations, binary logistic regression, and linear regression were used to analyze the data. The results indicated significant correlations between fine particle health-protective behaviors and cognitive function, which persisted even after adjusting for sociodemographic factors. These findings suggest that higher levels of protective behaviors are associated with better cognitive outcomes, highlighting the importance of interventions in aging populations. Further prospective studies are needed to determine whether fine particle health-protective behavior can help maintain cognitive function.

Association between air pollution exposure and brain cortical thickness throughout the lifespan: A systematic review

Increasing research has focused on the impact of air pollution on brain health. As the prevalence of air pollution is increasing alongside other environmental harms, the importance of studying the effects of these changes on human health has become more significant. Additionally, gaining insight into how air pollution exposure, measured at different points in the lifespan, can affect brain structure is critical, as this could be a precursor to cognitive decline later in life. The purpose of this review was to synthesize the literature on the association between air pollutant exposure and cortical thickness, a structural change with known associations with later cognition and neurodegenerative disease. After screening, twelve studies were included in this systematic review. Across a majority of studies, results suggest significant associations between increasing air pollution exposure and decreases in cortical thickness, primarily in areas such as prefrontal cortex, precuneus, and temporal regions of the brain. These results did differ somewhat between age groups and different air pollutants, with the most prominent results being found with exposure to PM2.5, the smallest particulate matter size included in the review. In the future, it is important to continue studying cortical thickness as it is essential to brain functioning and can be influential in disease progression. Furthermore, conducting more longitudinal studies in which air pollution is measured as a cumulation throughout the lifespan would help elucidate when exposure is most impactful and when brain structural changes become observable.

Association of ambient air pollution with cognitive functioning and markers of structural brain damage: The Maastricht study

INTRODUCTION

Given the absence of curative interventions and the rising global incidence of dementia, research is increasingly focusing on lifestyle factors for prevention. However, identifying shared environmental risk for dementia, next to individual factors, is crucial for optimal risk reduction strategies. Therefore, in the present study we investigated the association between air pollution, cognitive functioning, and markers of structural brain damage.

METHODS

We used cross-sectional data from 4,002 participants of The Maastricht Study on volumetric markers of brain integrity (white and grey matter volume, cerebrospinal fluid volume, white matter hyperintensities volume, presence of cerebral small vessel disease) and cognitive functioning (memory, executive functioning and attention, processing speed, overall cognition). Individuals were matched by postal code of residence to nationwide data on air pollution exposure (particulate matter < 2.5 μm (PM2.5), particulate matter <10 μm (PM10), nitrogen dioxide (NO2), soot). Potentia linear and non-linear associations were investigated with linear, logistic, and restricted cubic splines regression. All analyses were adjusted for demographic characteristics and a compound score of modifiable dementia risk and protective factors.

RESULTS

Exposure to air pollutants was not related to cognitive functioning and most brain markers. We found curvilinear relationships between high PM2.5 exposures and grey matter and cerebrospinal fluid volume. Participants in the low and high range of exposure had lower grey matter volume. Higher cerebrospinal fluid volumes were only associated with high range of exposure, independent of demographic and individual modifiable dementia risk factors. After additional post hoc analyses, controlling for urbanicity, the associations for grey matter volume became non-significant. In men only, higher exposure to all air pollutants was associated with lower white matter volumes. No significant associations with white matter hyperintensities volume or cerebral small vessel disease were observed.

DISCUSSION

Our findings suggest that higher PM2.5 exposure is associated with more brain atrophy.

Acute effects of ambient nitrogen dioxide pollution on outpatient visits for neurological diseases in Xinxiang, China

BACKGROUND

Accumulating evidence suggests that exposure to air pollution acts as a potential trigger for neurological diseases (NDs), yet the current knowledge regarding the impact of ambient nitrogen dioxide (NO2) on the patients with NDs remains limited. In this study, we conducted a time-series study to evaluate the association between short-term exposure to NO2 and hospital visits for NDs in Xinxiang, China.

METHODS

An over-dispersed Poisson generalized additive model was used to analyze the association between ambient NO2 concentrations and daily outpatient visits for NDs from January 1, 2015 to December 31, 2017. The model adjusted for meteorological factors, temporal trends, day of the week, and public holidays. The concentrations of air pollutants were collected from four air quality stations in Xinxiang.

RESULTS

A total of 38, 865 outpatient visits for NDs were retrieved during the study period. 86.5% of the patients were below the age of 65 years. It was revealed that a 10 µg/m3 increase in NO2 at lag 0 was associated with a significant rise of 1.50% (95% CI: 0.45-2.56%) in outpatient visits for NDs, which was stronger during the cold season. However, the overall results from stratified analyses did not reach statistical significance.

CONCLUSIONS

Short-term exposure to NO2 is associated with increased outpatient visits for NDs. These findings underscore the need for implementing mitigating measures to reduce the neurological health effects of air pollutants.

Effect of air pollutants particulate matter (PM2.5, PM10), sulfur dioxide (SO2) and ozone (O3) on cognitive health

Impaired cognitive health is the leading cause of various disabilities and disorders. Air pollution has been dramatically increasing over the last few decades and has been identified as a potential risk factor for impaired cognitive health. This study investigates the effect of air pollutants, particulate matter (PM2.5, PM10), sulfur dioxide (SO2), and ground-level ozone, on global cognitive health. The data on environmental pollutants and cognitive health were recorded from PubMed, Web of Science, Scopus, and Google Scholar. Initially, 790 articles were identified after screening for duplicates and applying the inclusion and exclusion criteria, 21 studies were included, and data was synthesized to get a pooled result. The overall results revealed that increased exposure to PM2.5 was positively and significantly associated with cognitive decline (OR 1.49; 95% CI 1.11, 1.99; p = 0.01). The risk of cognitive impairment due to PM10 (OR 1.30; 95% CI 1.00-1.70, p = 0.05), and SO2 (OR 1.39; 95% CI 1.27-1.51; p < 0.01) exposure were also significantly heightened. The study findings show that overall exposure to particulate matter PM2.5, PM10, and SO2 was associated with an increased risk of a decrease in global cognitive functions. The findings suggest that reducing levels of air pollutants could be a strategic approach to mitigate cognitive health risks in populations worldwide.

Effect of polycyclic aromatic hydrocarbon exposure on amnestic mild cognitive impairment and Alzheimer's disease: A matched case-control study

There is an emerging body of evidence concerning the neurological effect of air pollutants on cognitive function and increased risk of neurodegeneration. Although previous studies have suggested that polycyclic aromatic hydrocarbons (PAHs) are neurotoxic, the effect of PAHs exposure on neurodegeneration remains unclear. This study aimed to investigate the association between PAH exposure and the risk of developing amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD). For this matched case-control cross-sectional study, we recruited patients aged ≥50 years diagnosed with aMCI and AD from the Samsung Medical Center, Seoul, Korea, between 2014 and 2019. For each patient, we randomly selected four cognitively healthy controls through frequency matching based on sex, age group, and education level. Urinary levels of four PAH metabolites, 1-hydroxypyrene (1-OHP), 1-hydroxyphenanthrene (1-OHPhe), 2-hydroxyfluorene (2-OHFlu), and 2-naphthol (2-NAP), were measured. A conditional logistic regression model was used to evaluate the association, adjusting for potential confounders. A total of 212 patients with aMCI with 848 matched controls, and 267 patients with AD with 1068 matched controls were included in the analyses to estimate the risk of PAH exposure. We found that elevated urinary levels of PAH metabolites (specifically, 1-OHP and 2-NAP) were significantly associated with an increased risk of aMCI and AD. An increase of one unit in log-transformed level of urinary 1-OHP was associated with a 1.15- and 1.16-times higher risk of aMCI and AD, respectively. An increase of one unit in log-transformed level of urinary 2-NAP was associated with a 1.11- and 1.13-times higher risk of aMCI and AD, respectively. These findings indicate that PAH exposure may increase the risk of aMCI and AD, especially for the elderly population. Considering the widespread distribution of PAHs in the environment, reducing PAH exposure may be an effective strategy for the prevention of neurodegenerative diseases.

Machine learning and XAI approaches highlight the strong connection between O 3 and N O 2 pollutants and Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia with millions of affected patients worldwide. Currently, there is still no cure and AD is often diagnosed long time after onset because there is no clear diagnosis. Thus, it is essential to study the physiology and pathogenesis of AD, investigating the risk factors that could be strongly connected to the disease onset. Despite AD, like other complex diseases, is the result of the combination of several factors, there is emerging agreement that environmental pollution should play a pivotal role in the causes of disease. In this work, we implemented an Artificial Intelligence model to predict AD mortality, expressed as Standardized Mortality Ratio, at Italian provincial level over 5 years. We employed a set of publicly available variables concerning pollution, health, society and economy to feed a Random Forest algorithm. Using methods based on eXplainable Artificial Intelligence (XAI) we found that air pollution (mainly O 3 and N O 2 ) contribute the most to AD mortality prediction. These results could help to shed light on the etiology of Alzheimer's disease and to confirm the urgent need to further investigate the relationship between the environment and the disease.

Association of long-term exposure to various ambient air pollutants, lifestyle, and genetic predisposition with incident cognitive impairment and dementia

BACKGROUND

Long-term exposure to air pollution has been found to contribute to the development of cognitive decline. Our study aimed to assess the association between various air pollutants and cognitive impairment and dementia. Additionally, explore the modification effects of lifestyle and genetic predisposition.

METHODS

The exposure levels to various air pollutants, including particulate matter (PM) with diameters ≤ 2.5 (PM2.5), ≤ 10 (PM10), and between 2.5 and 10 μm (PM2.5-10) and nitrogen oxides (NO and NO2) were identified. An air pollution score (APS) was calculated to evaluate the combined exposure to these five air pollutants. A genetic risk estimate and healthy lifestyle score (HLS) were also generated. The Cox regression model adjusted by potential confounders was adopted to access the association between pollution exposure and cognitive decline, and several sensitivity analyses were additionally conducted to test the robustness.

RESULTS

The combined exposure to air pollutants was associated with an increased risk of incident cognitive decline. Compared with the low exposure group, the hazard ratio (HR) and 95% confidence interval (CI) for all-cause dementia, Alzheimer's dementia, vascular dementia, and mild cognitive impairment (MCI) in those exposed to the highest levels of air pollutants were respectively 1.07 (95% CI: 1.04 to 1.09), 1.08 (95% CI: 1.04 to 1.12), 1.07 (95% CI: 1.02 to 1.13), and 1.19 (95% CI: 1.12 to 1.27). However, the modification effects from genetic predisposition were not widely observed, while on the contrary for the healthy lifestyle. Our findings were proven to be reliable and robust based on the results of sensitivity analyses.

CONCLUSIONS

Exposure to air pollution was found to be a significant contributing factor to cognitive impairment and dementia, and this association was not easily modified by an individual's genetic predisposition. However, adopting a healthy lifestyle may help to manage the risk of cognitive decline related to air pollution.

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.

Particulate matter exposure and neurodegenerative diseases: A comprehensive update on toxicity and mechanisms

Exposure to particulate matter (PM) has been associated with a range of health impacts, including neurological abnormalities that affect neurodevelopment, neuroplasticity, and behavior. Recently, there has been growing interest in investigating the possible relationship between PM exposure and the onset and progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. However, the precise mechanism by which PM affects neurodegeneration is still unclear, even though several epidemiological and animal model studies have provided mechanistic insights. This article presents a review of the current research on the neurotoxicity of PM and its impact on neurodegenerative diseases. This review summarizes findings from epidemiological and animal model studies collected through searches in Google Scholar, PubMed, Web of Science, and Scopus. This review paper also discusses the reported effects of PM exposure on the central nervous system and highlights research gaps and future directions. The information presented in this review may inform public health policies aimed at reducing PM exposure and may contribute to the development of new treatments for neurodegenerative diseases. Further mechanistic and therapeutic research will be needed to fully understand the relationship between PM exposure and neurodegenerative diseases.

Ambient temperatures associated with reduced cognitive function in older adults in China

The cognitive function status of older adults determines the social function and living quality of older adults, which is related to the healthy development and stability of the society. However, the impact of high or low ambient temperature on cognitive function in older adults remains unclear. Based on data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS), we comprehensively assessed the impact of ambient temperature on the cognitive function of older adults in this study. The findings exhibited that for each 1 °C ascent in monthly temperature of high temperature, the examination score of global cognitive function of older adults decreased by 0.48 (95% CI 0.21-0.74), which was greater than that of 0.14 (95% CI 0.06-0.25) for each 1 °C reduction in low temperature. Overall, the detrimental effect of high temperature on cognitive function in older adults was more significant than that of low temperature, including on the five sub-cognitive functions involved. Our research provides vital technical guidance and reference for the health protection and prevention of cognitive function of older adults in specific external environmental conditions under the current climatic variation and temperature rise.

Particulate matter exposure from motorized traffic and risk of conversion from mild cognitive impairment to dementia: An Italian prospective cohort study

BACKGROUND

Based on epidemiologic and laboratory studies, exposure to air pollutants has been linked to many adverse health effects including a higher risk of dementia. In this study, we aimed to evaluate the effect of long-term exposure to outdoor air pollution on risk of conversion to dementia in a cohort of subjects with mild cognitive impairment (MCI).

METHODS

We recruited 53 Italian subjects newly-diagnosed with MCI. Within a geographical information system, we assessed recent outdoor air pollutant exposure, by modeling air levels of particulate matter with equivalent aerodynamic diameter ≤10 μm (PM₁₀) from motorized traffic at participants' residence. We investigated the relation of PM₁₀ concentrations to subsequent conversion from MCI to any type of dementia. Using a Cox-proportional hazards model combined with a restricted cubic spline model, we computed the hazard ratio (HR) of dementia with its 95% confidence interval (CI) according to increasing PM₁₀ exposure, adjusting for sex, age, and educational attainment.

RESULTS

During a median follow up of 47.3 months, 34 participants developed dementia, in 26 cases diagnosed as Alzheimer's dementia. In non-linear restricted spline regression analysis, mean and maximum annual PM₁₀ levels positively correlated with cerebrospinal fluid total and phosphorylated tau proteins concentrations, while they were inversely associated with β-amyloid. Concerning the risk of dementia, we found a positive association starting from above 10 μg/m³ for mean PM₁₀ levels and above 35 μg/m³ for maximum PM₁₀ levels. Specific estimates for Alzheimer's dementia were substantially similar. Adding other potential confounders to the multivariable model or removing early cases of dementia onset during the follow-up had little effect on the estimates.

CONCLUSIONS

Our findings suggest that exposure to outdoor air pollutants, PM₁₀ in particular, may non-linearly increase conversion from MCI to dementia above a certain ambient air concentration.