Air pollution could be making us less intelligent, especially men

Repeatedly inhaling nanoparticles found in air pollution may have a number of negative effects on the brain, including chronic inflammation of the brain's nerve cells.

Not only is air pollution bad for our lungs and heart, it turns out it could actually be making us less intelligent, too. A recent study found that in elderly people living in China, long-term exposure to air pollution may hinder cognitive performance (things like our ability to pay attention, to recall past knowledge and generate new information) in verbal and maths tests. As people age, the link between air pollution and their mental decline becomes stronger. The study also found men and less educated people were especially at risk, though the reason why is currently unknown.

We already have compelling evidence that air pollution – especially the tiniest, invisible particulates in pollution – damages the brain in both humans and animals. Traffic pollution is associated with dementia, delinquent behaviour in adolescents, and stunted brain development in children who attend highly polluted schools.

In animals, mice exposed to urban air pollution for four months showed reduced brain function and inflammatory responses in major brain regions. This meant the brain tissues changed in response to the harmful stimuli produced by the pollution.

We don’t yet know which aspects of the air pollution particulate “cocktail” (such as the size, number or composition of particles) contribute most to reported brain deterioration. However, there’s evidence that nanoscale pollution particles might be one cause.

These particles are around 2,000 times smaller than the diameter of a human hair, and can be moved around the body via the bloodstream after being inhaled. They may even reach the brain directly through the olfactory nerves that give the brain information about smell. This would let the particles bypass the blood-brain barrier, which normally protects the brain from harmful things circulating in the bloodstream.

Postmortem brain samples from people exposed to high levels of air pollution while living in Mexico City and Manchester, UK, displayed the typical signs of Alzheimer’s disease. These included clumps of abnormal protein fragments (plaques) between nerve cells, inflammation, and an abundance of metal-rich nanoparticles (including iron, copper, nickel, platinum, and cobalt) in the brain.

The metal-rich nanoparticles found in these brain samples are similar to those found everywhere in urban air pollution, which form from burning oil and other fuel, and wear in engines and brakes. These toxic nanoparticles are often associated with other hazardous compounds, including polyaromatic hydrocarbons that occur naturally in fossil fuels, and can cause kidney and liver damage, and cancer.

Repeatedly inhaling nanoparticles found in air pollution may have a number of negative effects on the brain, including chronic inflammation of the brain’s nerve cells. When we inhale air pollution, it may activate the brain’s immune cells, the microglia. Breathing air pollution may constantly activate the killing response in immune cells, which can allow dangerous molecules, known as reactive oxygen species, to form more often. High levels of these molecules could cause cell damage and cell death.

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