Lead Exposure Lowered IQ Scores of Half of Americans by 824 Million

Key Points

• A recent study revealed that approximately half of Americans had high levels of lead exposure during their childhood.
• This exposure resulted in an estimated loss of 824 million IQ points since the 1940s.
• In 1996, the U.S. government banned lead in gasoline.

Intelligence quotient (IQ) tests measure various factors, including cognitive abilities and education levels, to assess an individual's intellectual capacity. However, numerous factors influence a person's IQ score, as with many widely used tests.

According to a study published in the Proceedings of the National Academy of Sciences (PNAS), over 170 million Americans—about half of the population—experienced high levels of lead exposure during childhood. Consequently, they collectively lost an estimated 824 million IQ points since the 1940s.

Although lead is no longer used in gasoline, a significant proportion of water pipes in the United States still contain lead. This research could be valuable to city planners and public health experts working to protect the American public from exposure to toxic metals.

Background

In 1921, automotive engineers sought a solution to engine knocking, a phenomenon that could damage the engine and reduce a car's efficiency. They found that lead, a naturally occurring and now recognized toxic metal, was the answer. Subsequently, leaded gasoline became the primary fuel source in the United States.

However, the harmful health effects of lead soon became apparent. In 1924, the Surgeon General temporarily restricted leaded gasoline after 15 refinery workers were suspected to have died from lead poisoning. However, an investigating committee didn't find sufficient evidence to support this claim, and the Surgeon General allowed the continued use of leaded gasoline under voluntary standards.

The passage of the Clean Air Act in 1970 represented a turning point in reliance on leaded gas. The federal government established the Environmental Protection Agency (EPA), which began phasing out lead due to its increasingly understood health implications. Four years later, the EPA required at least one unleaded gasoline option compatible with cars manufactured in 1975 or later, equipped with catalytic converters that lead would harm.

Finally, in 1996, the EPA completely prohibited the use of leaded gasoline in on-road vehicles. As of July 2021, leaded gasoline is no longer available anywhere globally.

How Lead Affects the Body and Brain

How does lead exposure affect IQ scores, and why was its removal necessary? "Lead is a metal and chemical element naturally found in the environment. Unlike many other elements, lead has no biological role in the human body, acting instead as a toxin," explains Dr. Kelly Johnson-Arbor, medical toxicologist and co-medical director of the National Capital Poison Center.

According to the Centers for Disease Control and Prevention (CDC), short-term lead exposure can cause issues like memory loss, abdominal pain, constipation, headaches, and appetite loss. Long-term exposure can lead to depression, nausea, irritability, high blood pressure, kidney disease, and impotence. Certain populations face a higher risk associated with lead exposure.

"There is no known 'safe' level of lead in the human body, and even relatively low lead levels are associated with lower IQ scores and decreased academic progress in children." — Dr. Kelly Johnson-Arbor

Children are particularly vulnerable, as they absorb ingested lead at four to five times the rate of adults. Lead exposure can hinder their brain development, resulting in lower IQ scores, shorter attention spans, and antisocial behavior. It can also cause hypertension, comas, convulsions, or even death in children.

"There is no known 'safe' level of lead in the human body, and even relatively low lead levels are associated with lower IQ scores and decreased academic progress in children," says Johnson-Arbor. "Because of this, many states require blood testing for all children at a young age. Currently, a blood lead level of 3.5 mcg/dL is the accepted threshold limit for blood lead in children."

Pregnant women exposed to high levels of lead are at an increased risk of miscarriage, stillbirth, low birth weight, and premature labor.

The Institute for Health Metrics and Evaluation (IHME) reported that in 2019 alone, lead exposure worldwide caused an estimated 900,000 deaths and 21.7 million healthy life years lost. Low- and middle-income countries bore the brunt of this issue. In the same year, lead exposure was responsible for 62