Air pollution causes a huge reduction in intelligence, which is a frightening prospect when you consider that 95 percent of the world's population is breathing unsafe air.

The research, which was conducted in China and published in the journal Proceedings of the National Academy of Sciences, found that high pollution levels led to significant drops in test scores in language and arithmetic.  Men were impacted more than women, and language skills saw more erosion than math.  The longer people were exposed to dirty air, the bigger the damage to intelligence.

"Polluted air can cause everyone to reduce their level of education by one year, which is huge," said Xi Chen at Yale School of Public Health.  "But we know the effect is worse for the elderly, especially those over 64, and for men, and for those with low education.  If we calculate (the loss) for those, it may be a few years of education."

That could signiicantly disadvantage the elderly because "We usually make the most critical financial decisions in old age," according to Professor Chen.

This adds to the voluminous research showing that air pollution is just horrible for people.  Earlier studies linked air pollution to "extremely high mortality" in people with mental disorders and to increased mental illness in children.  One study found that people who live near busy roads had an increased risk of dementia.