Air pollution isn’t just bad for your lungs—it may be eroding your brain. In a sweeping review covering nearly 30 million people, researchers found that common pollutants like PM2.5, nitrogen dioxide, and soot are all linked to a significantly higher risk of dementia. The most dangerous? PM2.5—tiny particles from traffic and industry that can lodge deep in your lungs and reach your brain.
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In a paper published on July 24 in The Lancet Planetary Health, a team led by researchers at the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge, carried out a systematic review and meta-analysis of existing scientific literature to examine this link further. This approach allowed them to bring together studies that on their own may not provide sufficient evidence, and which sometimes disagree with each other, to provide more robust overarching conclusions.
In total, the researchers included 51 studies, including data from more than 29 million participants, mostly from high-income countries. Of these, 34 papers were included in the meta-analysis: 15 originated in North America, 10 in Europe, seven in Asia, and two in Australia.
The researchers found a positive and statistically-significant association between three types of air pollutant and dementia. These were:
- Particulate matter with a diameter of 2.5 microns or less (PM2.5), a pollutant made up of tiny particles small enough that they can be inhaled deep into the lungs. These particles come from several sources, including vehicle emissions, power plants, industrial processes, wood burning stoves and fireplaces, and construction dust. They also form in the atmosphere because of complex chemical reactions involving other pollutants such as sulphur dioxide and nitrogen oxides. The particles can stay in the air for a long time and travel a long way from where they were produced.
- Nitrogen dioxide (NO2), one of the key pollutants that arise from burning fossil fuels. It is found in vehicle exhaust, especially diesel exhaust, and industrial emissions, as well as those from gas stoves and heaters. Exposure to high concentrations of nitrogen dioxide can irritate the respiratory system, worsening and inducing conditions like asthma and reducing lung function.
- Soot, from sources such as vehicle exhaust emissions and burning wood. It can trap heat and affect the climate. When inhaled, it can penetrate deep into the lungs, aggravating respiratory diseases and increasing the risk of heart problems.
According to the researchers, for every 10 micrograms per cubic meter (μg/m³) of PM2.5, an individual’s relative risk of dementia would increase by 17%. The average roadside measurement for PM2.5 in Central London in 2023 was 10 μg/m³.
For every 10 μg/m3 of NO2, the relative risk increased by 3%. The average roadside measurement for NO2 in Central London in 2023 was 33 µg/m³.
For each 1 μg/m³ of soot as found in PM2.5, the relative risk increased by 13%. Across the UK, annual mean soot concentrations measured at select roadside locations in 2023 were 0.93 μg/m³ in London, 1.51 μg/m³ in Birmingham and 0.65 μg/m³ Glasgow.
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Several mechanisms have been proposed to explain how air pollution may cause dementia, primarily involving inflammation in the brain and oxidative stress (a chemical process in the body that can cause damage to cells, proteins, and DNA). Both oxidative stress and inflammation play a well-established role in the onset and progression of dementia. Air pollution is thought to trigger these processes through direct entry to the brain or via the same mechanisms underlying lung and cardiovascular diseases. Air pollution can also enter circulation from the lungs and travel to solid organs, initiating local and wide-spread inflammation.
The researchers point out that the majority of people included in the published studies were white and living in high-income countries, even though marginalised groups tend to have a higher exposure to air pollution. Given that studies have suggested that reducing air pollution exposure appears to be more beneficial at reducing the risk of early death for marginalised groups, they call for future work to urgently ensure better and more adequate representation across ethnicities and low- and middle-income countries and communities.
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Further analysis revealed that while exposure to these pollutants increased the risk of Alzheimer’s disease, the effect seemed stronger for vascular dementia, a type of dementia caused by reduced blood flow to the brain.
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Clare B Best Rogowski, Christiaan Bredell, Yan Shi, Alexandra Tien-Smith, Magdalena Szybka, Kwan Wai Fung, Lucy Hong, Veronica Phillips, Zorana Jovanovic Andersen, Stephen J Sharp, James Woodcock, Carol Brayne, Annalan Navaratnam, Haneen Khreis. Long-term air pollution exposure and incident dementia: a systematic review and meta-analysis. The Lancet Planetary Health, 2025; 101266 DOI: 10.1016/S2542-5196(25)00118-4
Source: Is the air you breathe silently fueling dementia? A 29-million-person study says yes | ScienceDaily
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