NEWS Mental Health News Past Century of Lead Exposure Lowered IQ Score of Half of Americans, Study Finds By Sarah Fielding Sarah Fielding LinkedIn Twitter Sarah Fielding is a freelance writer covering a range of topics with a focus on mental health and women's issues. Learn about our editorial process Updated on March 24, 2022 Fact checked Verywell Mind content is rigorously reviewed by a team of qualified and experienced fact checkers. Fact checkers review articles for factual accuracy, relevance, and timeliness. We rely on the most current and reputable sources, which are cited in the text and listed at the bottom of each article. Content is fact checked after it has been edited and before publication. Learn more. by Karen Cilli Fact checked by Karen Cilli Karen Cilli is a fact-checker for Verywell Mind. She has an extensive background in research, with 33 years of experience as a reference librarian and educator. Learn about our editorial process Share Tweet Email Print Catherine Falls Commercial / Getty Images Key Takeaways A new study found that an estimated half of Americans experienced high levels of exposure to lead during childhood.As a result, their collective IQ scores dropped about 824 million points since the 1940s.The government fully banned lead from gasoline in 1996. Intelligence quotient—or IQ—tests look at everything from a person’s cognitive abilities to education levels, presenting a supposedly standardized marker to assess individuals. However, like many other broadly distributed tests, a myriad of factors determine a person’s IQ score. A recent study from the Proceedings of the National Academy of Sciences (PNAS) found that over 170 million Americans—about half of the nation’s population—experienced high levels of lead exposure in childhood. As a result, they lost a total estimate of 824 million IQ points since the 1940s. There is no longer lead in our gasoline, but a large percentage of US water pipes contain lead. This research could further inform city planners and public health experts as they strive to keep the American public safe from toxic metals. History of Lead Exposure In 1921, automotive engineers were searching for a solution to engine knocking in cars—a phenomenon that could hurt the engine and lower the car’s efficiency. They discovered lead, a natural, now understood to be toxic, metal was the answer. As a result, leaded gasoline became the primary source of fuel in the United State However, it wasn’t long before the first signs of lead’s health ramifications emerged. In 1924, the Surgeon General temporarily restricted leaded gasoline after suspicion that 15 refinery workers had died from lead poisoning. Yet, the investigating committee didn’t find enough evidence to substantiate it, and the Surgeon General allowed leaded gas at voluntary standards. Thanks to the Clean Air Act’s passage, this reliance on leaded gas began to change in 1970. The federal government created the Environmental Protection Agency (EPA), which started phasing lead out due to its increasingly understood health ramifications. Four years later, the EPA took further steps by requiring at least one unleaded gasoline option compatible with cars created in 1975 or later. They were equipped with catalytic converters—a feature lead would damage. However, it wasn’t until 1996 that the EPA entirely banned the use of leaded gasoline in on-road vehicles. As of July 2021, leaded gasoline is not available anywhere in the world. The Health Risks of Cadmium in Cigarette Smoke Lead's Effect on the Body and Brain So, how can lead lower IQ points and why was it so necessary to remove it? “Lead is a metal and chemical element that is found naturally in the environment. Unlike many other elements, lead has no biological role in the human body,” says Dr. Kelly Johnson-Arbor, medical toxicologist and co-medical director of the National Capital Poison Center. Instead, lead acts as a toxin. According to Centers for Disease Control and Prevention, short-term lead exposure can cause issues such as 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 people have a higher risk associated with lead exposure. Kelly Johnson-Arbor, MD 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. — Kelly Johnson-Arbor, MD Children fall in that group as they absorb ingested lead at a rate of four to five times that of adults. Lead exposure can cause children to have brain development issues, causing issues such as a lower IQ score, smaller attention span, and antisocial behavior. It can also cause children to have hypertension, enter a coma, experience convulsions, or pass away. “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 that all children undergo blood testing at a young age. Currently, a blood lead level of 3.5 mcg/dL is the accepted threshold limit for blood lead in children.” In pregnant people, high levels of lead exposure causes a higher chance of miscarrying, 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 felt the brunt of this issue. In the same year, lead exposure caused 62.5% of global cases for developmental intellectual disability that didn’t have a clear cause. These factors are critical to keep in mind when looking at lead’s impact on IQ points. It’s also necessary to look at the disparities in lead exposure. As one of the study's researchers points out, Black children tended to have higher levels of lead exposure than white children. What This Means For You While lead is gone from gasoline, it can still exist in forms such as paint. If you believe you or another person has lead poisoning, call Poison Control: 1-800-222-1222. How the World's Lead Crisis Is Affecting Personality 5 Sources Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. McFarland MJ, Hauer ME, Reuben A. Half of US population exposed to adverse lead levels in early childhood. Proc Natl Acad Sci USA. 2022;119(11):e2118631119. doi:10.1073/pnas.2118631119 Environmental and Energy Study Institute. A brief history of octane in gasoline: From lead to ethanol. United Nations. End of leaded fuel use a 'milestone for multilateralism'. Centers for Disease Control and Prevention. Lead. World Health Organization. Lead poisoning. See Our Editorial Process Meet Our Review Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit Speak to a Therapist Online Advertiser Disclosure × The offers that appear in this table are from partnerships from which Verywell Mind receives compensation.