Childhood lead exposure reduced IQ scores for half of Americans, study says

Exposure to car exhaust from leaded gas slashed hundreds of millions of collective IQ points from about half of the Americans alive today, a new study reports.

Leaded gas, first used in 1923 to maintain engine integrity, reached peak usage in the 1960s and 1970s before being banned in 1996, according to the study. But despite that ban, Americans born before 1996 may be at increased risk for lead-related health issues, including faster aging of the brain, the study’s authors said in the Proceedings of the National Academy of Sciences on Monday. 

“Millions of us are walking around with a history of lead exposure,” co-author Aaron Reuben, a clinical psychology Ph.D candidate at Duke University, said in a statement.

“It’s not like you got into a car accident and had a rotator cuff tear that heals and then you’re fine,” he continued. “It appears to be an insult carried in the body in different ways that we’re still trying to understand but that can have implications for life.”

Lead, a neurotoxin, can erode brain cells once it enters the body, the authors noted, stressing that there is no safe level of exposure at any point in life. But young children are particularly vulnerable to lead due to the chemical’s ability to hinder brain function and decrease cognitive ability.

“Lead is able to reach the bloodstream once it’s inhaled as dust, or ingested, or consumed in water,” Reuben said. “In the bloodstream, it’s able to pass into the brain through the blood-brain barrier, which is quite good at keeping a lot of toxicants and pathogens out of the brain, but not all of them.”

Reuben, together with colleagues at Florida State University, looked at childhood blood-lead levels from 11,616 small children from 1976 to 2016 using data available from National Health and Nutrition Examination Survey. They combined these figures with leaded gas consumption data as well as population statistics to ascertain the “lifelong burden of lead exposure” of every American in 2015.

Drawing from these different data streams, they calculated that more than 170 million Americans had clinically concerning levels of lead in their blood when they were children.

This reality, according to the researchers, likely reduced IQs and put these individuals at heightened risk for long-term health effects such as smaller brain size, increased incidence of mental illness and greater chance of cardiovascular disease in adulthood.

Childhood exposure to leaded gasoline likely led to a collective plummet of 824 million IQ points — nearly three per American, the authors found. At its worst, they observed, individuals born in the mid-to-late 1960s may have lost up tosix  IQ points.

Those children who registered the highest levels of lead in their blood — eight times the current level that triggers clinical concern — may have lost an average of more than seven IQ points during this period, according to the study.

“I frankly was shocked,” Michael McFarland, study co-author and a professor of sociology at Florida State University, said in a statement. “And when I look at the numbers, I’m still shocked even though I’m prepared for it.” 

While a drop in just a few IQ points could seem negligible, the authors stressed that such changes are influential enough to shift a person with below-average cognitive ability — considered an IQ score less than 85 — to being categorized as having an intellectual disability, or one below 70.

“Essentially everyone born during those two decades are all but guaranteed to have been exposed to pernicious levels of lead from car exhaust,” the authors said.

After unearthing these stark findings, Reuben said that he now plans to examine the long-term impacts of past lead exposure on brain health in old age, citing previous studies suggesting that such exposure might quicken brain aging.

McFarland, meanwhile, said that among his next steps will be analyzing the racial disparities that have played into lead exposure, as Black children have historically been exposed more often to lead in comparison to their white peers.

While leaded gasoline may no longer be fueling American automobiles, aging infrastructure still conveys water via lead pipes in various parts of the country. November’s bipartisan infrastructure bill allocated $2.9 billion toward replacing such pipes, while the Biden administration announced further removal plans in December. 

In response to the latest findings in Monday’s study, Rep. Debbie Dingell (D-Mich.), who has long championed a fight to reduce childhood lead exposure, stressed the urgency of hastening these efforts.

Some 99,000 residents of Flint, Mich., were exposed to lead in their drinking water in 2014, while residents of Benton Harbor, Mich., are living with an ongoing lead contamination crisis.

“We know lead exposure causes immense suffering in our communities, especially for children and people of color,” Dingell told The Hill in a statement. “But we haven’t done nearly enough to rid our communities of this poison.”

“From Flint to Benton Harbor, Michigan knows the cost of inaction far too well,” she added. “We need to remove lead from all sources and rid it from our communities immediately.”