Air pollution is now an established risk factor for heart disease/stroke and respiratory disease, but its potential role in neurodegenerative diseases, such as dementia, isn’t clear. To try and explore this further, the researchers used carefully calculated estimates of air and noise pollution levels across Greater London to assess potential links with new dementia diagnoses. To do this, they drew on anonymized patient health records from the Clinical Practice Research Datalink (CPRD). This has been collecting data from participating general practices across the UK since 1987. For the purposes of this study, the researchers focused on just under 131,000 patients aged 50 to 79 in 2004, who had not been diagnosed with dementia, and who were registered at 75 general practices located within the London orbital M25 motorway. Based on the residential postcodes of these patients, the researchers estimated their yearly exposure to air pollutants-specifically nitrogen dioxide (NO2), fine particulate matter (PM2.5), and ozone (O3)-as well as proximity to heavy traffic and road noise, using validated modelling methods, validated with recorded measurements. The health of these patients was then tracked for an average of seven years, until a diagnosis of dementia, death, or deregistration from the practice, whichever came first. During the monitoring period, 2181 patients (1.7%) were diagnosed with dementia, including Alzheimer’s disease.