Medicine: Air pollution increases dementia risk

This connection has long been suspected, but now a comprehensive new study provides very valid evidence: Fine dust pollution increases the risk of developing dementia. This is the result of a meta-analysis recently published in the journal Lancet Planetary Health . For this analysis, researchers at the University of Cambridge evaluated a total of 51 studies with data from almost 50 million people, predominantly from high-income countries. The prerequisite was that the participants lived in an area with high levels of air pollution for at least one year.

Scientists had already discussed air pollution as a possible risk factor for dementia in previous studies. However, the research team writes that it was often not possible to establish a clear causal link. In some cases, these studies even contradicted each other.

The new work now allows a much more detailed look at the influence of air pollution, said geriatric psychiatrist and dementia specialist Tom Russ of the University of Edinburgh, who was not involved in the study, to the British Science Media Centre: "The data suggest, for example, that the risk of dementia from air pollution is nine percent lower in Edinburgh than in London."

The study can also determine more precisely which air pollutants pose the greatest problem. The authors specifically name three substances that increase the risk of dementia. These include particulate matter with a diameter of less than 2.5 micrometers, also known as PM2.5. These are so small that they can penetrate deep into the lungs and mainly come from vehicle exhaust, power plants, wood stoves, chimneys, and construction dust. According to the study, a person's relative risk of developing dementia increased by 17 percent for every 10 micrograms per cubic meter increase in PM2.5 concentration.

The World Health Organization (WHO) has long recommended that the annual average PM2.5 concentration should not exceed five micrograms per cubic meter of air. However, in urban areas, the values are often higher: According to the Federal Environment Agency, the average in Germany in 2024 was 9.1 micrograms per cubic meter .

The second identified pollutant, nitrogen dioxide, is primarily produced by the combustion of fossil fuels, but is also found in the exhaust fumes from gas stoves and heaters. According to the study, the risk of dementia increased by three percent for every ten micrograms per cubic meter of nitrogen dioxide. According to the Federal Environment Agency, the values fluctuate in Germany: Depending on the location of the measuring station, annual mean NO₂ values between 20 and 40 micrograms per cubic meter are measured near traffic, and in very isolated cases even higher.

For the third pollutant, soot, the researchers observed that for every increase of one microgram per cubic meter, the relative risk increased by 13 percent. In London, the average soot pollution at the roadside in 2023 was 0.93 micrograms per cubic meter.

But what does particulate matter pollution have to do with dementia? According to the authors, several mechanisms can be at play. Polluted air can trigger inflammatory processes and "oxidative stress," both of which contribute to cell, protein, and DNA damage. This has been proven to cause and progress dementia. Some airborne pollution particles can penetrate directly into the brain or cause so-called silent inflammation in the body, which in turn negatively impacts brain function.

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Several experts told the Science Media Centre that this connection needs further investigation. Neuroscientist Mark Dallas of the University of Reading emphasized: "We need to understand more precisely how these pollutants damage the brain." Future studies could also shed light on how air pollution affects different forms of dementia.

One of the authors of the meta-analysis, Christiaan Bredell of the University of Cambridge, emphasized in a statement that dementia prevention is not solely the responsibility of the healthcare system. This study shows that urban planning, transport policy , and environmental regulations also play an important role. However, the authors also point out that the study is based primarily on data from people in wealthy, predominantly white countries. Future studies should consider a broader demographic.