Lead exposure decreased IQs in older Americans, study suggests

A recent study by Duke University estimated that lead exposure has caused a decrease in the intelligence quotient (IQ) of more than 170 million Americans alive today, around half of the United States population.

The study was published in the journal Proceedings of the National Academy of Science and led by Michael McFarland, PhD, associate professor of sociology at Florida State University. The study analyzed data from the National Health and Nutrition Examination Survey (NHANE) that measured the blood-lead level (BLL) of nearly 12,000 children aged one to five from 1976 to 1980 to 2015 to 2016, along with population estimates from the U.S. Census, the Human Mortality Database, and the United Nations. Researchers estimated BBLs from 1940 to 1975 through data on leaded gas consumption and the NHANE.

Researchers found that BBLs were considerably higher among those born between 1951 to 1980 than those born after 2001. According to the study, since 2015, the average lead-linked loss in cognitive ability is 2.6 IQ points per person, reducing Americans cumulative IQ score by 824 million points. Scientists determined that those born between 1951 to 1980 have a disproportionate loss of IQ points among today’s population, estimating some lost up to 10 IQ points depending on the levels of lead in their blood as a child.

“Millions of us are walking around with a history of lead exposure,” said Aaron Reuben, study author and PhD candidate in clinical psychology at Duke University in a statement. “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.”

This study suggests that lead exposure may have negatively impacted the cognitive abilities of half of today’s U.S. population, highlighting how widespread the damage of environmental toxins can be. For future studies, Rueben said he wants to explore the long-term effects of lead exposure on brain health in old age.