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Lead exposure from car exhaust shrinks half of Americans' IQ scores

And falling IQ scores are only the beginning of the devastating consequences.

Lead exposure from car exhaust shrinks half of Americans' IQ scores
Exhaust fumes rise into the air. milehightraveler/iStock

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

Lead-based paint and lead-contaminated air, water, and soil are common sources of lead poisoning in children. But what if we told you that exposure to your car exhaust from leaded gas during childhood has stolen a significant number of your IQ points?

Automotive exhaust is a major way in which lead invades our bloodstreams. Lead was added to gasoline to improve engine performance and its consumption rose rapidly in the early 1960s and peaked in the 1970s.

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By the 1970s, health problems that stemmed from lead became apparent. In the United States, leaded gasoline for use in on-road vehicles was completely phased out as of January 1, 1996. Unfortunately, it was too late.

Reuben and his colleagues at Florida State University have found that essentially everyone born during those two decades is all but guaranteed to have been exposed to destructive levels of lead from car exhaust.

Their new study in the journal Proceedings of the National Academy of Sciences calculates that exposure to car exhaust from leaded gas during childhood robbed a collective 824 million IQ points from more than 170 million Americans alive today, which is about half the population of the United States.

Unsettling, to say the least. 

According to the study, Americans born before 1996 may now be at greater risk for lead-related health problems, such as faster aging of the brain. The researchers revealed that anyone born before the end of 1996, and especially those at the peak of the use of unleaded gas in the 1960s and 1970s, had alarmingly high levels of lead exposure as children. 

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Deadly implications

Lead is neurotoxic and can alter the normal activities of the central nervous system. Health experts have said that there is no safe level of exposure at any point in life.

The element is a silent killer - it works its way through the body, often over months or years.

The tiniest amounts of lead can cause serious health problems. Young children, especially those younger than six years, are highly vulnerable to lead poising, which can wreck mental and physical development. And at very high levels, lead poisoning can be lethal.

“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.”

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Reuben and his co-authors Michael McFarland and Mathew Hauer, both professors of sociology at Florida State University, knew that undertaking the impact of leaded gas use for over more than 70 years would be a complex task. So, they chose a simple strategy.

The researchers used publicly available data on U.S. childhood blood-lead levels, leaded gas use, and population statistics to determine the possible lifelong burden of lead exposure carried by every American alive in 2015. From the data, they gauged lead's assault on our intelligence by calculating IQ points lost from leaded gas exposure as a proxy for its harmful impact on public health.

The results startled them.

"I frankly was shocked,” McFarland said. “And when I look at the numbers, I'm still shocked even though I'm prepared for it."

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Long-term health effects 

As of 2015, more than half of the U.S. population had clinically concerning levels of lead in their blood when they were children. This likely resulted in lower IQs and put them at higher risk for other long-term health impairments, such as reduced brain size, greater likelihood of mental illness, and increased cardiovascular disease in adulthood.

Lead's toll on intelligence was horrifying: childhood lead exposure may have erased America's cumulative IQ score by an estimated 824 million points – nearly three points per person on average.

As per the researchers' calculations, people born in the mid-to-late 1960s may have lost up to six IQ points, and children registering the highest levels of lead in their blood, eight times the current minimum level to initiate clinical concern, fared even worse, losing more than seven IQ points on average.

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Though dropping a few IQ points may seem negligible, the researchers noted that these changes are sufficient to shift people with below-average cognitive ability (IQ score less than 85) to being classified as having an intellectual disability (IQ score below 70).

“It's not like you got into a car accident and had a rotator cuff tear that heals and then you’re fine. 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," said Reuben.

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