High air pollution in cities is “significantly” lowering children’s IQ, particularly among children from poorer backgrounds, according to research.

The double whammy of economic hardship and increased levels of smog from traffic has been shown to have a detrimental effect on children’s development by the time they are 7 years old, the study says.

The findings, produced by researchers at Columbia University, were published last month in the medical journal Neurotoxicology and Teratology.

The study followed 276 pairs of mothers and their children for seven years from pregnancy in New York city. It found that children from poorer backgrounds in areas of higher pollution scored lower in IQ tests by age 7 than those in more affluent areas with cleaner air.

However, researchers also found that within the group of mothers who reported that they were suffering from economic hardship, those children exposed to higher levels of pollutants scored “significantly lower” in IQ tests.

Frederica Perera, director of the Columbia Center for Children’s Environmental Health, said the study highlighted the need for greater action to be taken on reducing pollution in cities.

“The findings support policy interventions to reduce air pollution exposure in urban areas as well as programs to screen women early in pregnancy to identify those in need of psychological or material support,” Dr Perera said.

A previous study by the same researchers showed exposure to pollutants in the womb could lead to developmental delays among children by the age of 3, and “reduced verbal and full-scale IQ” by age 5, as well as symptoms of depression and anxiety by the age of 7.