Lead exposure from gasoline has lowered IQ scores for 170 million Americans

DURHAM, N.C. — More than half of the United States has lost almost four IQ points due to lead exposure in gasoline, a new study reveals. A team from Duke and Florida State University says that adds up to about 824 million IQ points lost among more than 170 million Americans alive today!

Researchers explain that manufacturers started adding lead to gasoline in 1923. The process helped to keep car engines functioning, but it turns out it also came with a great price to human health.

Due to car exhaust and other avenues of contamination, the study finds exposure to leaded gas during childhood has created long-term and possibly life-long health issues for people living in this era. This damage includes accelerated aging in the brain.

The U.S. government banned leaded gasoline in 1996. However, researchers say anyone born before this date was exposed to concerningly high levels of lead during their childhood. People born in the 1960s and 1970s — during the peak of leaded gasoline use — are particularly at risk, according to the study.

What makes lead so dangerous?

Lead is a neurotoxin which erodes brain cells if these particles enter the body. Studies show there are no safe levels of lead exposure at any point in a person’s life. However, exposure to lead is especially dangerous for children because of its ability to impair brain development and lower cognitive functioning.

Moreover, lead is one of the few substances that can penetrate the blood-brain barrier and directly impact a person’s brain in a negative way.

“Lead is able to reach the bloodstream once it’s inhaled as dust, or ingested, or consumed in water,” says Aaron Reuben, a PhD candidate in clinical psychology at Duke, in a university release. “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.”

One of the main ways study authors say lead particles entered the bloodstream over the last century is through car exhaust.

A decades-long impact on American intelligence

Researchers used public data on blood-lead levels in U.S. children, leaded gas usage, and population statistics to estimate the impact on Americans still living in 2015. Those figures revealed that more than 170 million people had “clinically concerning levels” of lead in their blood during childhood.

The impact of that exposure resulted in lower IQ scores as well as a higher risk of smaller brain size and a greater likelihood of developing mental illness or heart disease during adulthood.

Overall, the average American born before 1996 has lost between three and four IQ points due to lead exposure. Americans born during the peak of leaded gas usage in the 1960s may have lost up to six IQ points. For children with the highest levels of lead exposure, researchers estimate they lost more than seven IQ points.

“I frankly was shocked,” says study co-author Michael McFarland. “And when I look at the numbers, I’m still shocked even though I’m prepared for it.”

Losing a few IQ points may not sound like a completely life-altering problem, but study authors argue that it’s a concerning issue for people with below-average cognitive ability. This group includes people with an IQ lower than 85. However, dropping below 70 allows doctors to classify someone with having an intellectual disability — making every point count.

“Millions of us are walking around with a history of lead exposure,” Reuben concludes. “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.”

The findings are published in the journal Proceedings of the National Academy of Sciences.

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