According to a new study, exposure to lead from gasoline in early childhood may have blunted the IQ of nearly half of the current U.S. population.

The study, published in the journal Proceedings of the National Academy of Sciences, found that over 170 million Americans alive today were born and raised during the heyday of gasoline containing lead and were consequently exposed to high lead levels during their childhood.

That exposure likely caused the loss of nearly a billion IQ points among that population, study researchers concluded.

The researchers from Florida State University and Duke University found the peak era of leaded gasoline in the U.S. ran from the late 1960s to the early 1980s. During that time, the average blood-lead level for the general U.S. population was three to five times higher than the current reference value for clinical concern, 3.5 micrograms of lead per deciliter of blood.

“Consequently, millions of adults alive today were exposed to high levels of lead as children. While these exposures were deemed harmless at the time, animal studies and epidemiological evidence accrued in the intervening years reveal that such exposure likely disrupted healthy development across multiple organ systems, resulting in subtle deficits to important outcomes, such as cognitive ability, fine motor skills and emotional regulation that may influence the trajectory of a person’s life,” the study’s authors concluded.

The U.S. banned leaded gasoline in 1996, but the researchers found that the development deficits persisted over time and, in some cases, worsened, putting some people at risk for chronic and age-related diseases, including cardiovascular disease and dementia.