“Epidemiological evidence plays a crucial role in allowing us to determine whether or not air pollution increases the risk of dementia and by how much. Our work provides further evidence to support the observation that long-term exposure to outdoor air pollution is a risk factor for the onset of dementia in previously healthy adults,” said senior author of the study, Dr Haneen Khreis, of the MRC Epidemiology Unit at the University of Cambridge School of Clinical Medicine, in a press release.
For the study, researchers conducted a systematic review and meta-analysis of 34 studies examining long-term exposure to outdoor air pollutants, characterized as a year or more, and a physician diagnosis of dementia. While 15 of the studies originated from North America, 10 were from Europe, seven from Asia, and two from Australia.
Ultimately, the researchers found a positive and statistically significant link between dementia and three types of air pollutants: particulate matter with a diameter of 2.5 microns or less (PM2.5), nitrogen dioxide, and soot. Each 10 micrograms per cubic meter (μg/m³) of PM 2.5 was found to increase an individual’s relative risk of dementia by 17%. For a sense of scale, the average roadside measurement of PM2.5 in Central London was 10 μg/m³ in 2023.
Meanwhile, each 10 μg/m3 of NO2 increased the relative risk of dementia by 3%. The average roadside measurement of NO2 in London in 2023 was 33μg/m3. As for soot, each 1 μg/m³ of soot was linked to a 13% higher risk of dementia. The annual mean soot concentrations assessed at roadside locations in the UK in 2023 included 0.93 μg/m³ in London and 1.51 μg/m³ in Birmingham.
“These findings underscore the need for an interdisciplinary approach to dementia prevention. Preventing dementia is not just the responsibility of healthcare: this study strengthens the case that urban planning, transport policy, and environmental regulation all have a significant role to play,” said first author of the study, Dr. Christiaan Bredell of the University of Cambridge and North West Anglia NHS Foundation Trust, in a press release.
Sources: EurekAlert, The Lancet Planetary Health
