Air pollution confirmed as a major risk factor for dementia

The air we breathe may do more than harm our lungs – it could also be quietly raising our risk of dementia.

A global analysis of data from nearly 30 million people suggests that air pollution – particularly from vehicle exhaust – significantly increases the risk of Alzheimer’s and vascular dementia.

Dementia currently affects over 57 million people. The number is projected to rise to almost 153 million by 2050. Although some areas such as Europe and North America are witnessing minor declines in prevalence, the global view is much less reassuring.

Researchers from the University of Cambridge’s Medical Research Council Epidemiology Unit took a closer look at the connection between pollution and dementia.

By combining results from 51 studies conducted across several continents – 34 of which qualified for meta-analysis – the experts were able to draw on a larger and more dependable data pool.

Which pollutants raise dementia risk?

The analysis focused on three major air pollutants: PM2.5, nitrogen dioxide (NO₂), and soot.

PM2.5, or fine particulate matter, consists of tiny particles small enough to reach deep into the lungs. These particles are generated by sources such as vehicle exhaust, industrial processes, wood burning, and construction dust.

Nitrogen dioxide, a byproduct of burning fossil fuels, is commonly found in vehicle emissions – especially from diesel engines. This gas is known to worsen asthma and reduce lung function.

Soot comes from sources like diesel exhaust and wood fires. It not only harms the environment but can also reach deep into the lungs, contributing to respiratory and heart problems.

Air pollution’s role in dementia

The findings were clear: for every 10 micrograms per cubic meter (μg/m³) increase in PM2.5, the relative risk of developing dementia rose by 17 percent. For the same increase in NO₂, the risk increased by three percent.

For each 1 μg/m³ rise in soot, the relative dementia risk rose by 13 percent. To put that in context, in 2023, the average roadside PM2.5 level in Central London was 10 μg/m³ – the same amount linked to a 17% higher dementia risk.

London’s average NO₂ level stood at 33 μg/m³. Roadside soot levels were 0.93 μg/m³ in London, 1.51 μg/m³ in Birmingham, and 0.65 μg/m³ in Glasgow.

Tackling air pollution for public health

“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,” said Dr. Haneen Khreis.

“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.”

According to Dr. Khreis, tackling air pollution can deliver long-term health, social, climate, and economic benefits. “It can reduce the immense burden on patients, families, and caregivers, while easing pressure on overstretched healthcare systems.”

How does air pollution affect the brain?

The health impacts appear to go beyond just Alzheimer’s. The researchers found the association between air pollution and dementia was slightly stronger for vascular dementia, which is caused by reduced blood flow to the brain.

Around 180,000 people in the UK alone are affected by this type of dementia.

How does air pollution impact the brain? Researchers have identified several possible mechanisms.

The most widely supported theories involve inflammation and oxidative stress – both of which can damage cells, proteins, and even DNA. These processes are already linked to other chronic diseases.

Pollutants may enter the brain directly, or indirectly via the bloodstream, after first affecting the lungs or heart. Once in the brain, they can trigger the kind of inflammation known to contribute to dementia.

Equity gap in air pollution studies

The review also highlighted a gap in the current research: most of the studies were conducted in high-income countries and focused on predominantly white populations.

This matters because marginalized communities often face higher exposure to pollution, yet they remain underrepresented in research.

“Efforts to reduce exposure to these key pollutants are likely to help reduce the burden of dementia on society,” said study co-first author Clare Rogowski.

“Stricter limits for several pollutants are likely to be necessary targeting major contributors such as the transport and industry sectors. Given the extent of air pollution, there is an urgent need for regional, national, and international policy interventions to combat air pollution equitably.”

Environmental fixes to fight dementia

The team argues that solutions can’t just come from doctors or healthcare workers. Urban design, environmental policy, and transportation planning all play a role.

“These findings underscore the need for an interdisciplinary approach to dementia prevention,” said Dr. Christiaan Bredell.

“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.”

The message is clear: reducing air pollution isn’t just a public health priority – it’s a critical step toward protecting brain health on a global scale.

The full study was published in the journal The Lancet Planetary Health.

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