A new study from Duke University and Florida State University suggests exposure to the lead contained in car fumes may have stolen millions of IQ points from Americans over the past century – particularly for individuals born before 1996. 

What You Need To Know

  • A new study from Duke University and Florida State University suggests exposure to the lead contained in car fumes may have stolen millions of IQ points from Americans over the past century

  • Individuals born before 1996, when the U.S. had phased out the use of lead in gasoline, were the most impacted and are now more likely to face health issues as a result of the exposure

  • The scientists found 90% of children born in the U.S. between 1950 and 1981 had blood-lead levels higher than the CDC threshold, which resulted in a 2.6-point drop in IQ

  • The researchers only examined lead exposure caused by leaded gasoline, the dominant form of exposure from the 1940s to the late 1980s, according to data from the U.S. Geological Survey

The United States began using tetraethyl lead in its gas for cars in the 1920s after scientists at General Motors discovered it could improve the engine functionality. By the 1970s, as the health impacts of lead became more widely known, companies began to phase out the use of lead in gasoline. By Jan. 1, 1996, the U.S. had completely phased out the use of lead in gas. 

The new study, published Monday in the medical journal Proceedings of the National Academy of Sciences, found that individuals born before 1996 – and in particular, those who were children in the 1960s and 1970s, at the height of the lead use in gasoline – had “concerningly high lead exposures as children.” Those adults are now more likely to face health issues as a result of the exposure, like faster aging of the brain.

"Lead is able to reach the bloodstream once it's inhaled as dust, or ingested, or consumed in water," lead study author Aaron Reuben said in a statement. "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."

Experts have long said lead, a toxic metal found in a number of products, “can be harmful to human health even at low exposure levels,” but is most harmful when inhaled, as the body breathes in more lead particles from the fumes. Young children and infants are particularly vulnerable to health risks and developmental delays from lead exposure, as they are affected by lower doses of the toxin than adults.  

The Duke and Florida State researchers implemented a fairly simple method to determine the potential impact of lead exposure on Americans’ IQ. By using public data on childhood blood-lead levels, leaded-gas use and population statistics, the group was able to determine the “likely lifelong burden of lead exposure carried by every American alive in 2015.”

They estimated that half the U.S. adult population in 2015 had been exposed to lead levels surpassing five micrograms per deciliter — the Centers for Disease Control and Prevention threshold for harmful lead exposure at the time.

The scientists also found that 90% of children born in the U.S. between 1950 and 1981 had blood-lead levels higher than the CDC threshold. And the researchers found a significant impact on cognitive development: on average, early childhood exposure to lead resulted in a 2.6-point drop in IQ.

While a 2.6 drop in IQ is likely negligible for the vast majority of the population, the authors note it may impact those with below-average cognitive ability – or an IQ score less than 85 points – to being classified as intellectually disable, or having an IQ score below 70.

The researchers only examined lead exposure caused by leaded gasoline, the dominant form of exposure from the 1940s to the late 1980s, according to data from the U.S. Geological Survey.

Michael McFarland, an associate professor of sociology at Florida State University, said the findings were “infuriating” because it was long known that lead exposure was harmful, based on anecdotal evidence of lead’s health impacts throughout history.

Previous research on the relationship between lead exposure and IQ found a similar impact, though over a shorter study period.

Bruce Lanphear, a health sciences professor at Simon Fraser University in Vancouver who has researched lead exposure and IQ, said his 2005 study found the initial exposure to lead was the most harmful when it comes to loss of cognitive ability as measured by IQ.

“The more tragic part is that we keep making the same ... mistakes again,” Lanphear said. “First it was lead, then it was air pollution. ... Now it’s PFAS chemicals and phthalates (chemicals used to make plastics more durable). And it keeps going on and on.

“And we can’t stop long enough to ask ourselves should we be regulating chemicals differently,” he said.

The Associated Press contributed to this report.