A major new analysis has found that long-term exposure to air pollution, especially from car exhaust and other common sources, increases the risk of developing dementia.
The study, led by scientists at the University of Cambridge and Trinity College Dublin, looked at data from almost 30 million people and found strong links between air pollution and diseases like Alzheimer’s and vascular dementia.
Dementia affects more than 57 million people around the world today, and that number is expected to rise to over 150 million by 2050.
It has serious impacts not just on those with the condition, but also on families, caregivers, and healthcare systems.
While some countries have seen a small drop in dementia rates, in many parts of the world the numbers are still rising.
Recent research has suggested that breathing polluted air might be one factor that increases the risk of dementia.
To find out more, the Cambridge-led team reviewed 51 studies from around the world, involving over 29 million people. These studies came from North America, Europe, Asia, and Australia.
The researchers focused on three types of air pollution: PM2.5 (tiny particles small enough to enter the lungs), nitrogen dioxide (NO2), and soot. PM2.5 comes from things like car exhaust, factories, power plants, and even wood-burning stoves.
NO2 is mostly released when fossil fuels are burned, including in cars and gas appliances. Soot is a black powdery substance found in smoke from cars and burning wood.
They found that for every increase of 10 micrograms per cubic meter (μg/m³) of PM2.5, a person’s risk of developing dementia increased by 17%. The same increase in NO2 raised the risk by 3%, while even just a 1 μg/m³ increase in soot raised the risk by 13%. These are levels commonly found in cities around the world.
The findings show that breathing polluted air may cause harmful inflammation and chemical damage in the brain. The particles can enter the body through the lungs and may even reach the brain, where they cause stress to cells and lead to conditions that trigger or worsen dementia. These same processes are also involved in heart and lung diseases.
Importantly, most of the people included in the study were white and lived in wealthier countries. But studies show that people from poorer and minority communities are more exposed to pollution and may benefit more from efforts to reduce it.
The scientists say future research must better include people from different backgrounds and countries to fully understand the risks.
The researchers also found that pollution may increase the risk of vascular dementia—caused by poor blood flow to the brain—even more than it increases the risk of Alzheimer’s. But there were not enough studies to say this for certain.
The authors of the study say that preventing dementia isn’t just a job for doctors and nurses. Urban planners, environmental agencies, and governments must work together to reduce pollution from transport and industry.
Better policies, cleaner air, and fairer health protections could reduce the number of people developing dementia in the future.
This research was supported by the European Union’s Horizon 2020 and Horizon Europe research funding programs.
If you care about dementia, please read studies about Early heart rhythm problem linked to higher dementia risk and findings of Green leafy vegetables may help reduce Alzheimer’s risk.
For more about dementia, please read studies about Research shows an important cause of frontotemporal dementia and findings of New way to detect Lewy body disease early, a leading cause of dementia.
The study is published in The Lancet Planetary Health.
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