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Air pollution linked to increased risk of stroke and dementia transition, study reveals

In a recent study published within the journal eClinicalMedicine, researchers assess the detrimental effects of long-term air pollution exposure on the dynamic transitions of stroke and dementia, especially the influence of air pollution during different time intervals, using the UK (UK) Biobank data.



Study: Ambient air pollution and the dynamic transitions of stroke and dementia: a population-based cohort study. Image Credit: okanozdemir/Shutterstock.com

Specifically, they evaluated the health effects of multiple air pollutants in ambient air. This comprised a mix of each particulate matter (PM) and gaseous pollutants.

Background

The final result of stroke could be fatal, especially amongst aged people. Stroke accounts for 11.6% of all global deaths and is a number one reason for neurological death and disability worldwide.

In 2019, greater than 50 million people had dementia. That is projected to extend to 152 million by 2050.

Given the non-availability of interventions to forestall dementia onset and fatal stroke outcomes, investigation of the alterable risk aspects of each conditions stays a priority.

Notably, each stroke and dementia create reciprocal risks, which necessitates investigation of the chance aspects involved within the “transition” from stroke to comorbid dementia and dementia to comorbid stroke.

Moreover, emerging evidence suggests that the chance from stroke or dementia to comorbidity varies with the duration of the disease. Thus, studying its impacts (that changes over time) could possibly be critical to optimizing prevention and management strategies for stroke or dementia.

Study methodology

In the current study, researchers first calculated the air pollution rating using levels of pollutants: PM2.5, PM2.5-10, PMcoarse, and nitrogen dioxide (NO2), measured within the study area using passive samplers.

Next, they combined these measurements with residential addresses (of participants) to develop LUR models to elucidate any significant spatial variance in air pollutants.

Finally, they created an air pollution rating using principal components evaluation (PCA) based on the measured pollutants. The team followed up with all participants until lost to follow-up, death, or February 2020.

The researchers then identified stroke and dementia cases using the UK Biobank data from death registries and hospitals.

They used Cox proportional hazard models to evaluate the associations of air pollution with stroke, dementia, comorbidity, and all-cause mortality. Multi-state models were used to find out the association of air pollution with the dynamic transitions of stroke and dementia. 

The outcomes, i.e., each interquartile range (IQR) increase in air pollution rating and individual air pollutants, were presented as hazard ratios (HRs) with 95% confidence intervals (CIs).

The study models further stratified the observed associations between air pollution and transitions based on age (<65 vs. ≥65 years), gender (female vs. male), Townsend deprivation index (

Finally, they performed several sensitivity analyses to evaluate the robustness of the outcomes.

Results

Of 413,372 participants (54.2% females) included in the first evaluation, the number of people diagnosed with stroke or dementia during a ten.9-year follow-up period was proportionally low: 6,484 (1.6%) with stroke and three,813 (0.9%) with dementia.

Some participants were diagnosed with each conditions; 238 participants with stroke developed dementia, and 138 participants with dementia suffered a stroke.

Cox proportional hazard and competing risk models revealed positive associations between air pollution, specifically increased PM2.5 and NO2, dementia, comorbidity of each conditions and all-cause mortality. Likewise, multi-state models showed a link between air pollutants and dynamic transitions of stroke and dementia.

Potential confounders didn’t markedly modify the observed association between air pollution and transitions from stroke or dementia to comorbidity, and the study results also remained robust in sensitivity analyses.

The present US Environmental Protection Agency (EPA) annual standards for air pollution are PM2.5: 12 μg/m3, NO2: 53 ppb, and the boundaries of the UK and the European Union (EU) are PM2.5: 20 μg/m3, NO2: 40 μg/m3 and PM2.5: 25 μg/m3, NO2: 40 μg/m3, respectively.

The study found that air pollutants below these standards were also related to the transition from stroke to comorbid dementia, with increased risks inside one yr and over five years after stroke, with the HR of 1.61 and 1.82 (95% CI) for every IQR increase within the air pollution rating, respectively. 

Although air pollution had no association with the general transition from dementia to comorbid stroke, it still adversely impacted this transition during 2–3 years, with an HR of 1.75 (95% CI) for every IQR increase in air pollution rating.

Conclusions

The study findings provide novel evidence for reducing the chance of neurological disorders related to air pollution during critical time intervals. 

Considering that many countries’ air quality standards are still above the World Health Organization (WHO) Global Air Quality standards, updated in 2021, implementing stricter controls for air pollution could help alleviate the burden of those diseases.

Moreover, research on pathophysiological mechanisms governing these associations is required.

Journal reference:

Wang J, Hu X, Yang T, et al. (2023). Ambient air pollution and the dynamic transitions of stroke and dementia: a population-based cohort study. eClinicalMedicine. doi: 10.1016/j.eclinm.2023.102368. https://www.nature.com/articles/s44324-023-00002-

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