Dozens of vehicles driving in traffic at nightShare on Pinterest
Air pollution related to traffic may have negative effects on cognitive health. Pictorial Parade/Getty Images
  • One in 10 Americans ages 65 and older is estimated to have dementia.
  • One of the 12 modifiable risk factors for dementia is air pollution.
  • Researchers from the Western University, London, Ontario, Canada found that higher exposure to particulate matter in traffic-related air pollution increases a person’s dementia risk.
  • Scientists say a person’s dementia risk increases by 3% for every one microgram per cubic meter of fine particulate matter they were exposed to.

According to recent research, one in 10 Americans ages 65 and older has dementia — a group of diseases that impair the way the brain functions.

Although there is no cure for dementia, scientists have identified 12 modifiable risk factors that may help lower a person’s risk for dementia.

One of those risk factors is air pollution. Previous research links air pollution exposure to increased hospital admission risk for dementia. And another study found exposure to high levels of air pollution increased older women’s risk of dementia by over 90%.

Now, adding to this body of research is a new study from a team at Western University, London, Ontario, Canada, that found higher exposure to particulate matter in traffic-related air pollution is linked to an increased risk of dementia. Scientists found a person’s dementia risk increased by 3% for every one microgram per cubic meter of fine particulate matter they were exposed to.

This study was recently published in Neurology, the medical journal of the American Academy of Neurology.

Recent statistics show that 99% of the world’s population lives in an area that does not meet the organization’s air quality guidelines, making air pollution one of the biggest environmental health risks.

Particulate matter — also called particle pollution — is a type of air pollution made up of extremely tiny pieces of solid particles mixed with liquid droplets. These solid particles can include dust, dirt, smoke, or soot, which are large enough to see, but it is the very fine particles, less than 2.5 micrometers, that worry researchers the most. This is because they can penetrate deep into the lungs and pass into the bloodstream. These tiny particles are about 30 times smaller than a human hair.

Particle pollution comes from a variety of sources, including:

  • transportation vehicles
  • industrial factories
  • forest fires
  • coal burning
  • construction sites
  • agricultural processes

“Fine particulate matter is not a homogenous entity — it is mainly composed of inorganic ions, metals, and organic matter,” explained Dr. Ehsan Abolhasani, lead author of this study, researcher in the Department of Psychiatry at McGill University, and past graduate research assistant in the Department of Epidemiology and Biostatistics at Western University, London, Ontario, Canada.

“It can also carry other viruses and hazardous molecules into the human body,” he said.

Because of its small size, Dr. Abolhasani said PM2.5 can escape immune cells in the lungs, spread into the bloodstream, and cross the barriers of the brain.

“In the brain, it can cause reactions such as inflammation and can have toxic effects on cells, leading to neuron death. In addition, PM2.5 is associated with cardiovascular disease, which may also contribute to (the) risk of dementia,” he told Medical News Today.

A study earlier this year found air pollution was responsible for 9 million premature deaths in 2015.

Dr. Abolhasani said there have been numerous studies showing an association between air pollution and the incidence of dementia, but sometimes with contradictory results.

“Therefore, we decided to evaluate all available studies on such an association and draw a conclusion about the association between (the) incidence of dementia and chronic exposure to traffic-related air pollutants, especially fine particulate matter,” he said.

For this study, researchers evaluated data from 17 studies examining a correlation between air pollution and dementia risk. Participants in all studies were over the age of 40. Of the more than 91 million participants the researchers assessed through the 17 studies, 5.5 million or 6% of them developed dementia.

All the studies exploring the relationship between fine air pollution (PM2.5) adjusted for other factors associated with dementia, such as age, sex, smoking, and alcohol. Most of the research adjusted for educational level, weight, and physical activity levels.

Globally people living in poverty are more likely to live in more polluted areas, although this relationship is not so clear in European studies. Most of the studies included in this meta-analysis did adjust for some measure of poverty, such as income or Medicaid eligibility.

The research team also found the participants who did not develop dementia had a lower average daily exposure to fine particulate matter. Additionally, the team found for every one microgram per cubic meter (µg/m3) increase of fine particulate matter exposure, a person’s dementia risk increased by 3%.

“The pooled 3% increase in risk is clinically important since the recommended safe level of exposure is approximately 10 to 12 μg/m3,” Dr. Abolhasani explained.

“A number of studies in Asia, India, and Africa have reported average exposures ranging from 29 to 42 μg/m3. While we cannot determine a precisely safe level of exposure to prevent dementia, we should consider ways to decrease traffic-related air pollution in urban areas to reduce the risk of dementia.”
— Dr. Ehsan Abolhasani

As for the next steps in this research, Dr. Janet Martin, a member of the research team, said they planned to further evaluate global dementia trends to detect whether there is a relationship between effective policies to reduce air pollutants and downward trends in new cases of dementia.

Dr. Martin is an associate professor in the Department of Anesthesia & Perioperative Medicine and Department of Epidemiology & Biostatistics at the Schulich School of Medicine & Dentistry at Western University, London, Ontario, Canada.

“Based on this evidence, we plan to advocate for policies that meaningfully reduce the risk of dementia for our generation, and future generations to come. Without a clear plan of action, dementia will only become a bigger problem,” she told MNT.

“If ambient exposure to higher concentrations of fine particulate matter is a risk factor for dementia, this provides a discrete, actionable focal point for efforts at the national and global level to find ways to reduce PM2.5 to safer levels, while supporting healthy growth and innovation across all countries.”
— Dr. Janet Martin

“Given this knowledge, we now need to explore which policies work best to contain PM2.5 levels below safe thresholds, while still supporting healthy urban societies full of opportunities for growth and innovation,” Dr. Martin added.

Medical News Today also spoke with Dr. Scott Kaiser, a geriatrician and director of Geriatric Cognitive Health for the Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA, about this research.

He said there are many ways by which air pollution could drive dementia risk, including causing inflammation of the brain and nervous system, oxidative stress, and harmful impacts on the lungs and heart.

“And under it all, we know that air pollution increases the risk of heart disease and stroke, and vascular damage in the brain. And we know that underlying vascular pathology along with neurodegeneration drives the risk for dementia, too,” he continued.

As air pollution is a modifiable risk for dementia, Dr. Kaiser said there are some protective measures people can take. For example, he suggested not exercising around high-traffic areas or when air quality is low.

“There are air boards that give air quality ratings, and even in your weather app (on your phone) [where] you can see information about particulate matter and air quality,” he explained.

“(Being) particularly mindful of when there’s a lot of particulate matter in the air and when the air quality is bad to heed those warnings and not exercise outdoors when it’s unsafe [to] exercise outdoors … could go a long way.”
— Dr. Scott Kaiser

Dr. Kaiser said this study points to what we can do collectively to create and advocate for cleaner air.

“There’s still a lot more that needs to be done in terms of understanding the pathways by which air pollution increases this risk, but also what we can do about it, What we need to do to create brain-healthier environments. And that’s exciting to think about a whole generation of work that can illuminate that path forward,” he said.