Breathing polluted air can cloud your mind–permanently.

Air pollution reduces intelligence, especially verbal intelligence. The effects build over time, and get worse with age. Hardest hit are older men with little formal education.

Air Pollution Lowers Test Scores

Xin Zhang, a statistician at Beijing Normal University; Xi Chen, an economist and Assistant Professor of Public Health at Yale; and Xiabao Zhang, senior research fellow at the International Food Policy Research Institute in Washington, DC, who also teaches economics at Peking University, set out to discover how air pollution is affecting the intelligence of people in developing nations. They published their results in the Proceedings of the National Academy of Science in September, 2018.

The researchers matched intelligence test scores of 20,000 people in China with data about air pollution and weather conditions at the time and place of the tests. They also broke the results down by age and gender.

They found that in places with more air pollution, people scored much lower on verbal intelligence tests.

Air Pollution Impacts Men’s Brains Most

The level of air pollution had a bigger effect on men’s test scores. The study’s authors suspect that is because of structural differences in male and female brains.

Our brains have two main kinds of tissue.

Gray matter is mostly made up of the bodies of brain cells. It is abundant in parts of the brain responsible for movement, sensation, emotion, speech, and decision making. Women have more gray matter in their brains.

White matter is mostly made of cells that carry messages from one part of a brain to another. Men have more white matter in their brains.

Air pollution damages the white matter of the brain. Since men’s brains have more white matter, it effects them more.

Air Pollution and the Aging Brain

The effects of air pollution are also worse on the brains of older people than they are on the brains of younger people.

Damage to white matter may be to blame here as well. We develop most of our gray matter as children and teenagers. We keep producing more white matter well into middle age.

White matter naturally begins deteriorating around age sixty. The less active your brain is, the faster the white matter breaks down.

So, aging people’s white matter is already breaking down. Less educated people are less likely to keep their minds active. Men are impacted most by this because more of their brains are white matter. Air pollution speeds up that deterioration. This lines up with the study’s main finding: air pollution does the most damage to older, less educated men.

The High Cost of Brain Damage from Air Pollution

Zhang, Zhang, and Chen say this brain damage from air pollution has high social and economic costs. Declining verbal intelligence is linked to declines in decision making, memory, cognition, and people’s ability to take care of themselves.

The problem is worst in the countries that can least afford to pay those costs. The twenty most polluted cities are all in developing countries.

Brain damage from air pollution may become a very expensive problem as more and more people become less and less able to take care of themselves as they age.