The meta-analysis reviewed 17 studies of traffic-related air pollution.
This is according to a meta-analysis recently published in Neurology, the medical journal of the American Academy of Neurology, higher exposure to a certain type of traffic-related air pollution known as particulate matter may be linked to an increased risk of dementia. Researchers focused on particulate matter, or PM2.5, which consists of airborne pollutants less than 2.5 microns in diameter. The meta-analysis examined all available studies on the relationship between air pollution and the risk of dementia.
“As people live longer, conditions such as dementia are becoming more common, so detecting and understanding preventable risk factors is key to reducing the rise in this disease,” said study author Ehsan Abolhasani, MD, MSc, of Western University in London, Canada. “Since a World Health Organization report shows that more than 90% of the world’s population lives in areas with higher than recommended levels of air pollution, our results provide more evidence for enforcing air quality regulations and accelerating the transition from fossil fuels to renewable energy.”
17 studies were analyzed by the researchers for the meta-analysis. Participants had a minimum age of 40 years. More than 91 million individuals participated in all studies. 5.5 million of them, or 6%, developed dementia.
The studies took into account age, gender, smoking, education level and other variables that can increase or decrease a person’s risk of dementia.
Researchers analyzed levels of air pollution exposure for people with and without dementia and found that people without dementia had lower average daily exposures to fine particulate air pollutants. The US Environmental Pollution Agency (EPA) considers an average annual exposure of up to 12 µg/m3 safe.
Researchers found that the risk of dementia increased by 3% for every microgram per cubic meter (µg/m3) increase in particulate matter exposure.
“While our meta-analysis does not prove that air pollution causes dementia, it only shows an association. We hope that these findings empower people to take an active role in reducing their exposure to pollution,” Abolhasani said. “Understanding the risk of dementia from exposure to air pollution can help people take steps to reduce their exposure, such as using renewable energy, choosing to live in areas with less pollution, and advocating for less traffic pollution in residential areas.”
They also looked at nitrogen oxides, which make up smog, nitrogen dioxide and ozone exposure, but found no significantly increased risk when looking at these other classes of pollutants alone.
A limitation of the meta-analysis was the small number of available studies on this specific topic. Abolhasani said more studies are needed.
Reference: “Air Pollution and Incidence of Dementia: A Systematic Review and Meta-Analysis” By Ehsan Abolhasani, Vladimir Hachinski, Nargess Ghazaleh, Mahmoud Reza Azarpazhooh, Naghmeh Mokhber, and Janet Martin, October 26, 2022, Neurology.