Half of Americans alive today were exposed to “clinically concerning” lead levels during their childhood — and their IQ scores shrank as a result, a new study found.

Specifically, an estimated 824 million IQ points of more than 170 million Americans, who were adults as of 2015, were lost from childhood exposure to car exhaust from leaded gas, according to a Duke University news release. Leaded gas was banned from fueling new U.S. vehicles in 1996 after it was added to gasoline starting in 1923.

On average, nearly three IQ points were stolen from each American cognitively impacted from leaded gas exposure before 1996, according to researchers from Duke and Florida State University.

Those born before the 1996 ban “may now be at greater risk for lead-related health problems, such as faster aging of the brain,” the release said of the study published March 7 in Proceedings of the National Academy of Sciences.

Leaded gasoline use peaked during the […]