published in the Proceedings of the National Academy of Sciences.
In addition, the researchers found, 90% of children born in the United States between 1951 and 1980 had blood-lead levels higher than the Centers for Disease Control and Prevention threshold. On average, early childhood exposure to lead resulted in a 2.6-point drop in IQ per person.
“Most of what we think of as the Lost Generation and the Greatest Generation and Baby Boomers had a moderate amount of lead exposure,” Matt Hauer, PhD, one of the coauthors and an assistant professor of sociology at Florida State University, Tallahassee, said in a statement.
“Generation X was exposed to very high amounts of lead, and now Millennials and the generation following them have been exposed to very low amounts of lead,” he said.
The findings were “infuriating” because scientists have long known that lead exposure is harmful, Michael McFarland, PhD, coauthor and an associate professor of sociology at Florida State University, Tallahassee, told The Associated Press.
The research team analyzed blood-lead levels, census data, and the use of leaded gasoline to understand how widespread early childhood lead exposure was in the United States between 1940 and 2015. They looked mostly at exposure caused by leaded gasoline, which was the dominant form of exposure between the 1940s and 1980s.
They estimated that half of the U.S. adult population in 2015 had been exposed to lead levels that surpassed 5 micrograms per deciliter, which was the CDC threshold at the time. More than 54 million had been exposed to levels above 15 micrograms per deciliter, and 4.5 million were exposed to 30 micrograms per deciliter – or six times the threshold.
They found that estimated lead-linked deficits were greatest for the 21 million people born between 1966 and 1970, who had an average 5.9-point drop in IQ per person.
The United States has put in place tougher regulations to protect Americans from lead poisoning in recent decades, particularly from gasoline. The study team found that blood-lead levels were considerably lower than 5 micrograms per deciliter among those born since 2001.
At the same time, the public health effects of childhood exposure for older generations will last for years to come.
“Childhood lead exposure is not just here and now. It’s going to impact your lifelong health,” Abheet Solomon, a senior program manager at the United Nations Children’s Fund, told the AP.
Childhood lead exposure is known to affect the development of mental skills, and it raises the risk of hypertension, kidney damage, and heart disease. It has been linked to harm in pregnant women and developing children.
“The more tragic part is that we keep making the same … mistakes again,” Bruce Lanphear, MD, a health sciences professor at Simon Fraser University in Vancouver, B.C., told the AP.
Dr. Lanphear’s research on lead exposure has found loss of mental skills and IQ as well.
“First it was lead, then it was air pollution. Now it’s PFAS chemicals and phthalates (chemicals used to make plastics more durable),” he said. “And we can’t stop long enough to ask ourselves should we be regulating chemicals differently.”
A version of this article first appeared on WebMD.com.