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Air Pollution and the Brain, Part 1

Several recent studies have highlighted the negative effects of air pollution on the brain, specifically from the tiniest particles in polluted air (called PM 2.5). These tiny particles get to the human brain and cause all sorts of damage. Even at levels within government guidelines.

Two studies found that with higher chronic (daily) exposure to PM2.5 air pollution there were structural changes to the brain. Which is negative to brain health, of course.

With chronic exposure to higher levels of  PM2.5 air pollution: one study found greater declines in memory and more Alzheimer's-like brain atrophy in older women in the USA; and the second study found that higher prenatal exposure was associated with a smaller corpus callosum (a part of the brain) later in childhood. Thus structural changes in the brain!

The tiniest particles are 2.5 micrometers or less in diameter, about 1/30th the width of human hair - and referred to as PM2.5. These fine particles are produced by all sorts of combustion, including motor vehicles, power plants, residential wood burning, agricultural burning, some industrial processes, and forest fires. Typically there is much more exposure to PM2.5 in busy urban streets, and less in quiet suburban streets.

Researchers in Barcelona, Spain found that long-term higher prenatal exposure to PM2.5 particulate matter, especially during the last trimester of pregnancy, is associated with a smaller corpus callosum in children between the ages of 8 and 12 years. This is an important finding because a smaller (reduced volume) corpus callosum is found in ADHD (attention deficit hyperactivity disorder), ASD (autism spectrum disorder), and hyperactivity. So here we see a structural change in the brain from air pollution at PM2.5 levels that are considered acceptable (within guidelines) by the European Union!

A report called The State of Global Air/2018 stated that studies show that long-term exposure to PM2.5  particles in the air "is the most consistent and robust predictor" of death from heart disease and stroke, lung cancer, and respiratory illnesses. And then there are nitrogen oxides and ozone, which are also linked to death. There are also nanoparticles (e.g., from friction of tires being used) that penetrate deep into the human body.

A 2018 The Guardian article called air pollution "the new tobacco". And that it's time to tackle this epidemic. Yup. Unfortunately, current air pollution standards are being relaxed in all sorts of ways under the current U.S. administration. Beware!

First study. Excerpts from Medical Xpress: Exposure to PM 2.5 pollution linked to brain atrophy, memory decline 

Women in their 70s and 80s who were exposed to higher levels of air pollution experienced greater declines in memory and more Alzheimer's-like brain atrophy than their counterparts who breathed cleaner air, according to USC researchers.

"This is the first study to really show, in a statistical model, that air pollution was associated with changes in people's brains and that those changes were then connected with declines in memory performance," said Andrew Petkus, assistant professor of clinical neurology at the Keck School of Medicine at USC.

Fine particles, also called PM2.5 particles, are about 1/30th the width of a human hair. They come from traffic exhaust, smoke and dust and their tiny size allows them to remain airborne for long periods, get inside buildings, be inhaled easily, and reach and accumulate in the brain. Fine particle pollution is associated with asthma, cardiovascular disease, lung disease and premature death. 

For this study, researchers used data from 998 women, aged 73 to 87, who had up to two brain scans five years apart as part of the landmark Women's Health Initiative. ... When all that information was combined, researchers could see the association between higher pollution exposure, brain changes and memory problems—even after adjusting to take into account differences in income, education, race, geographic region, cigarette smoking and other factors.

Second study. Excerpts from Medical Xpress: Prenatal exposure to pollution linked to brain changes related to behavioral problems

Over the past few decades, various studies have investigated the impact of air pollution on cognitive capacities in children. ... A new study led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by "la Caixa," has found a link between air pollution and changes in the corpus callosum, a region of the brain associated with neurodevelopmental disorders such as attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD).

In the new study, researchers examined the relationship between prenatal exposure to particulate matter (PM2.5) in urban air and the size of the corpus callosum in children. A total of 186 children from 40 schools in Barcelona were included in the study. 

The findings show that prenatal exposure to particulate matter, especially during the last trimester of pregnancy, can induce structural changes in the corpus callosum in children between the ages of 8 and 12 years. Specifically, an increase of 7 μg/m3 in PM2.5 level was associated with a nearly 5% decrease in the mean volume of the corpus callosum.

"Our findings are cause for concern for various reasons," commented Jordi Sunyer, leader of the study and head of the Childhood and Environment Programme at ISGlobal. "First, in the cases of chronic prenatal exposure we studied, the PM2.5 levels were below the limit value of 25 μg/m3 established by the European Union. Second, reduced volume of the corpus callosum is a common characteristic of ADHD and ASD, although it is not an alteration specific to these disorders. Finally, children with a 5% reduction in corpus callosum volume showed higher levels of hyperactivity."

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