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Childhood Lead Exposure Lowered IQ Of Over 50 Percent Of US Adults


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer


These two are screwed. Image: Vasilyev Alexandr/Shutterstock

Things only true nineties kids remember: Pogs; this noise; and losing IQ points through regular exposure to toxic levels of lead.

“I frankly was shocked,” commented Michael McFarland, a professor of sociology at Florida State University. He’s co-author of a new paper, published in the Proceedings of the National Academy of Sciences, which has revealed something pretty startling: as of 2015, over half of Americans are living with the after-effects of a childhood spent with clinically concerning levels of lead in their blood.


“When I look at the numbers, I'm still shocked,” McFarland added. “Even though I'm prepared for it."

What numbers, you ask? According to the study, childhood exposure to lead has taken a collective 824 million IQ points from over 170 million Americans alive today.

That’s not all: the cumulative effects of lead are permanent, ranging from impacting brain and nervous system development in children, to damaging the kidneys and cardiovascular system in adults, to miscarriage and stillbirth. Researchers have connected lead exposure with aggressive and criminal behavior, some even thinking it might have been a factor in the fall of the Roman Empire.

“It's not like you got into a car accident and had a rotator cuff tear that heals and then you’re fine,” explained Aaron Reuben, who also co-authored the paper. “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.”


Where did these sky-high levels of lead come from? The answer is simple: our cars. See, while we were all in grade school laughing at Elizabethans painting their faces with a toxic heavy metal, adults were busy pumping that same stuff straight into the gas canister of their ‘91 Honda Accord.

Leaded gasoline first hit the market in 1923, and even though everybody involved knew it was poisonous and the factories producing it were literally known as “loony gas buildings” because of the neurological effects of lead exposure on the workers, it stayed there over 70 years.

Thanks to those exhaust fumes, “millions of us are walking around with a history of lead exposure,” said Reuben.

“Lead is able to reach the bloodstream once it’s inhaled as dust, or ingested, or consumed in water,” he explained. “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.”


What does that mean for the average person? Using publicly available data from places like the CDC, the team attempted to calculate lead exposure's long-term health burden on Americans today. On average, Americans alive in 2015 were down three IQ points due to the metal’s widespread addition to gasoline – a measurement they used as a proxy for its harmful impact on public health more generally.

For some people, the news is even worse. Leaded gas was available in the US up until 1996, but its use peaked in the 1960s and 70s – people born in those decades are pretty much guaranteed to have been exposed to “pernicious” lead levels from car exhausts, the researchers say.

For these generational cohorts, the calculated IQ loss was as much as six or seven points – over twice as much as for the average American. That might not sound like a lot, but as the researchers note, it’s dramatic enough to potentially shift people with below-average cognitive ability – an IQ less than 85 – to being classified as having an intellectual disability – defined as having an IQ below 70.

These findings are likely just the beginning of the story. Childhood lead exposure has been linked to accelerated brain aging, and the team hopes to investigate the long-term effects of lead exposure in old age.


Like so many public health issues, the problem of lead exposure follows a noticeable racial divide – and MacFarland hopes his future research can highlight the unequal burden that has been suffered by Black communities in the US.

After that, it’s just a question of taking on the millions of American children being poisoned by lead in the water supply, and we’ll finally be a step ahead of the Ancient Romans.


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