An analysis involving data from nearly 30 million people has linked long-term exposure to outdoor air pollution, including car exhaust emissions, to an increased risk of dementia. Dementias like Alzheimer's disease currently affect over 57.4 million individuals worldwide, a number projected to rise to 152.8 million by 2050.
The study, published in The Lancet Planetary Health and led by researchers at the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge, conducted a systematic review and meta-analysis of existing literature on the topic. This comprehensive approach provided more robust conclusions about the connection between air pollution and dementia.
In total, 51 studies were reviewed with data from more than 29 million participants exposed to air pollutants for at least one year. A meta-analysis included data from North America, Europe, Asia, and Australia. The findings indicated a significant association between three types of air pollutants—PM2.5, nitrogen dioxide (NO2), and soot—and dementia.
For PM2.5, each increase of 10 micrograms per cubic meter (μg/m³) raised the relative risk of dementia by 17%. For NO2, a similar increase resulted in a 3% higher risk. Each additional microgram per cubic meter of soot increased the risk by 13%.
Dr Haneen Khreis from the MRC Epidemiology Unit stated: "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." She emphasized that tackling air pollution could deliver health benefits while easing pressure on healthcare systems.
The research also explored how air pollution may cause dementia through inflammation in the brain and oxidative stress. Air pollution can enter circulation from the lungs and trigger these processes.
The study highlighted that most participants were white and living in high-income countries despite marginalized groups facing higher exposure levels. Clare Rogowski from the MRC Epidemiology Unit called for stricter pollutant limits targeting major contributors like transport and industry sectors.
Further analysis suggested stronger effects on vascular dementia compared to Alzheimer's disease but noted limited studies on this difference.
Dr Christiaan Bredell emphasized an interdisciplinary approach to preventing dementia: "Preventing dementia is not just the responsibility of healthcare."
The research was funded by the European Research Council under Horizon 2020 and Horizon Europe Framework Programme.