The longitudinal relationships between the built and natural environment, air pollution, noise and dementia: results from two UK-based cohort studies

Objective Recent epidemiological studies have investigated a variety of environmental risk factors for dementia. However, most existing studies have focused on single environmental factors and reported mixed results. The aim of this study is to examine the interrelationships between multiple environment factors and their joint associations with cognitive health in later life. Methods This study was based on the Cognitive Function and Ageing Study II and Wales, two population-based cohort studies of 11,055 people aged ≥65 across five urban and rural areas in the UK. Using geospatial data, a wide range of environmental variables were generated for the participants and integrated into five domains through a latent approach, including the built environment, natural environment, noise, air pollution and deprivation. Multistate modelling was used to investigate their longitudinal associations with dementia and death adjusting for individual sociodemographic factors. Results The effect sizes of joint associations between the built environment (HR: 1.00; 95 %CI: 0.66, 1.52), natural environment (HR: 0.95; 95 %CI: 0.66, 1.36), air pollution (HR: 0.91; 95 %CI: 0.78, 1.07), deprivation (HR: 1.02; 95 %CI: 0.96, 1.09) and incident dementia were generally small. The strongest association was found in noise, where a high level of exposure was associated with an increased risk of incident dementia (HR: 1.22; 95 %CI: 0.97, 1.54). However, the confidence intervals were wide. Conclusions The joint associations between multiple environmental factors and incident dementia were found to be modest. Given mixed results in this field, future research should address methodological challenges and enhance evidence for population-level interventions on dementia risk factors.