What Caused Millions of Americans To Lose IQ Points?
A new study found that exposure to lead from gasoline stunted the IQ of about half the U.S. population.
The peer-reviewed study, published in the journal Proceedings of the National Academy of Sciences, focuses on people born before 1996 — the year the U.S. banned gas containing lead.
Researchers from Florida State University and Duke University found childhood lead exposure cost America an estimated 824 million points, or 2.6 points per person on average.
Certain age groups were affected more than others. Those born at the peak of leaded gas consumption in the 1960s and the 1970s lost up to 7 IQ points. Exposure primarily came from inhaling auto exhaust.
Researchers studied gas consumption data, population estimates, and other data to calculate that as of 2015, more than 170 million Americans had blood lead levels above 5 micrograms per deciliter in their early childhood years.
Currently, 3.5 micrograms per deciliter is the reference value for high blood lead levels, though the amount used to be much higher. But lead is a neurotoxin, and no amount of it is safe.
“This is important because we often think about lead as an issue for children, and of course it is,” said Michael McFarland, the study’s principal author and an associate professor of sociology at Florida State University. “But what we really wanted to know is what happens to those children who were exposed?”
McFarland said that a 2 to 3 point IQ difference is nominal, unless an individual is on the lower side of IQ distribution.
“If you’re more toward cognitive impairment, a couple points can mean a lot,” he said.
While there are medical interventions available for children who have recently been exposed to high amounts of lead, those wouldn’t work for adults born before 1996.
Still, the study findings should not be a major cause for concern, McFarland said.
“There are a host of things that go into IQ,” he said. “This is one that is obviously negative, but if you also have a nurturing home environment, that helped your IQ.”