The association between air pollution and dementia: results from the Cognitive Function and Ageing Study II and Wales

Abstract

AbstractBackgroundAir pollution has been recognised as one of the key modifiable risk factors for dementia. In the UK, there is a lack of evidence from population‐based cohort studies including older people from different backgrounds and living environments. Using two multicentre ageing cohorts in England and Wales, the aim of this study is to investigate the potential impact of air pollution on dementia in later life.MethodThis study was based on the Cognitive Function and Ageing Study (CFAS) II (2008‐2011) and Wales (2011‐2013), two longitudinal studies of people aged 65 or above across five centres in England (Cambridgeshire, Newcastle upon Tyne, Nottingham) and Wales (Gwynedd, Neath Port Talbot). A two‐year follow‐up wave was carried out for both studies. Dementia was identified using the Geriatric Mental State and its diagnostic algorithm, Automated Geriatric Examination for Computer Assisted Taxonomy (GMS‐AGEACT). Based on the participants’ postcodes at the baseline, exposure to four air pollutants in 2012, including nitrogen dioxide (NO2), ozone (O3), particulate matter with a diameter ≤10 microns (PM10) and ≤2.5 microns (PM2.5), was estimated using the Community Multiscale Air Quality pollution modelling at a resolution of 20×20 m. Multistate modelling was used to investigate the effects of air pollution exposure on risk of developing dementia over the follow‐up period, incorporating mortality (from national death certification) and adjusting for age, sex, education, study centre and area deprivation.ResultAmong the 11329 participants in CFAS II (N = 7753) and Wales (N = 3576), the median exposure was 17.7 (IQR = 11.6) µg/m3 for NO2, 43.8 (IQR = 11.1) µg/m3 for O3, 15.5 (IQR = 3.1) µg/m3 for PM10 and 10.1 (IQR = 2.8) µg/m3 for PM2.5 and large variation was observed across the five centres. Per unit increase in NO2 exposure was associated with a higher risk of dementia in CFAS II (HR: 1.07; 95%CI: 1.03, 1.12) but not the Welsh cohort (HR: 0.93; 95%CI: 0.86, 1.00) after adjustment. For the other air pollutants, the associations were unclear.ConclusionOur study suggests limited evidence for the impacts of air pollution on dementia. Other environmental factors may influence individual exposure to air pollution and altogether have a complex effect on cognitive health in later life.