Hypothetical Ambient Fine Particulate Matter Interventions and Dementia Risk: Causal Effect and the Role of Cardiovascular Disease

Date of Award

Spring 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Public Health

First Advisor

Chen, Kai

Abstract

Dementia is a syndrome of progressive decline in cognitive ability, including memory loss, and deterioration of logical thinking, learning, and reasoning. Given the significant physical health burden caused by dementia and the corresponding emotional and monetary impacts, identifying modifiable risk factors is essential for prevention, as there is currently no effective treatment. Fine particulate matter (i.e., particulate matter with an aerodynamic diameter less than or equal to 2.5μm [PM2.5]), a common air pollutant, is a potentially modifiable risk factor. Implementing policies aimed at reducing ambient PM2.5 levels could have a broad impact as an intervention measure for the general population. Although the association between PM2.5 and dementia risk has been observed in epidemiological studies, there is limited evidence on the causal effect of stricter ambient PM2.5 standards on dementia risk. This information is crucial for policymakers to weigh the costs of PM2.5 reduction against the potential health benefits. Additionally, since achieving immediate reductions in ambient PM2.5 levels may not always be feasible, it is essential to identify mediators in the PM2.5-dementia relationship and evaluate the impact of intervening on the mediator in mitigating dementia risk when lower PM2.5 levels have not been achieved. In this dissertation, we applied causal inference methods to observational data from the UK Biobank, a large-scale cohort in the United Kingdom, to estimate the effects of hypothetical ambient PM2.5 interventions with stricter standards on the risk of dementia and risk of hospitalization for major cardiovascular diseases. We also quantified the proportion of the effect of not achieving more stringent PM2.5 standards on dementia risk that could be mitigated by intervening on cardiovascular disease. Our findings indicate that policies aimed at reducing ambient PM2.5 levels have a beneficial effect in reducing the risk of dementia and major cardiovascular diseases. Furthermore, the promotion of cardiovascular health has the potential to reduce the burden of dementia. These results provide direct information for policymakers and medical practitioners to develop strategies for reducing the burden of dementia in the current and future population.

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