Half of the US adult population may have a lower IQ from harmful levels of lead exposure in childhood, study finds

• Up to 170 million Americans may have been exposed to harmful levels of lead as children.
• A new paper estimates leaded gasoline exposure caused cognitive impairment, and a population-wide drop in IQ.

Exposure to leaded gasoline decades ago may have lowered the IQ of US adults, new research suggests.

More than 170 million Americans alive today may have been exposed to dangerous levels of lead as children, potentially causing brain development issues, according to a paper published March 7 in the Proceedings of the National Academy of Sciences.

Researchers from Florida State University and Duke University looked at health survey, census, and consumer data to calculate how many Americans may have been exposed to harmful levels of lead through leaded gasoline.

They found that 50% of Americans who were adults as of 2015 had likely been exposed to levels of lead high enough to impair cognitive function. The estimated result, researchers calculated, may be a reduction of the adult population IQ by an average of 2.6 points per person as of 2015.

The results were shocking, according to researchers, and could have ongoing consequences for public health.

"Millions of us are walking around with a history of lead exposure," Aaron Reuben, coauthor of the study and a PhD candidate at Duke University said in a press release. "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."

Even small amounts of lead can cause brain damage and developmental issues

High levels of lead can cause neurotoxicity which can cause a wide range of neurological symptoms, and exposure can build up over time, according to the Mayo Clinic.

In some cases, lead poisoning can be fatal. Exposure over time can be especially risky for children, causing learning disabilities, mood regulation problems, hearing loss, or seizures, according to the Mayo Clinic.

Leaded gasoline, popular in the late 1960s, was a common source of lead exposure through the 1980s, researchers found in the current paper, though the EPA began efforts to phase it out in 1973.

In the same period, levels of lead in the blood were three to five times the safe limit recommended by the CDC at the time, according to the paper.

People currently in their late 40s to mid 50s may have experienced the worst cognitive damage from lead exposure, estimated at between 5.7 to 5.9 lost IQ points per person, researchers estimated. In some cases, estimated exposure may have been significant enough to cause cognitive impairments in the range of intellectual disability (an IQ below 70), according to the paper.

The researchers only looked at gasoline as a source of lead exposure in the study, but the toxic metal can also be found in homes, drinking water, and in some cases, contaminated food.

Previous research found children today may still face high levels of lead exposure

While leaded gasoline was banned in 1996, lead exposure continues to be an issue, and disproportionately affects people in poorer communities with aging infrastructure.

A 2021 study found that risky levels of lead exposure were found in just over 50% of children younger than five years old, tested between 2018 and 2020.

Common sources of exposure include lead paint and lead pipes in housing built prior to the 1950s.