Leaded gas fueled most vehicles on the road beginning in 1923, when it was first added to gasoline to keep car engines healthy, until 1996, when it was banned in the United States after being linked to widespread cognitive damage in children. For the new study, researchers used data on leaded-gas use, childhood blood-lead levels, and population trends to estimate the lifetime amount of lead exposure for every American alive in 2015. On average, childhood lead exposure cut Americans’ IQ scores by 3 points, according to study results reported in the Proceedings of the National Academy of Sciences.
Peak Leaded Gasoline Use Tied to Effects in 1960s and 1970s
The damage was doubled, however, for people born during the 1960s and 1970s, when leaded gasoline usage hit its zenith in the United States, the study found. Typical levels of childhood lead exposure during these decades resulted in an average IQ score reduction of six points, with even larger hits to IQ for those with the highest levels of lead exposure. “I frankly was shocked,” says the lead study author Michael McFarland, PhD, an associate professor of sociology at Florida State University in Tallahassee.
Every IQ Point Matters in Cognitive Classification
Losing just a few IQ points might be enough to shift some people with average cognitive ability — IQ scores of 85 to 115 — to below average — with IQ scores below 85. It might also mean that people who would be below average without any lead exposure would shift to the intellectually disabled classification — an IQ below 70 — because of lead poisoning, the researchers point out. There is no safe level of lead exposure, according to the Centers for Disease Control and Prevention (CDC). And lead poisoning can cause a wide range of serious, lasting health problems, including lower IQ, attention deficits, reduced brain size, and an increased risk of mental illness and cardiovascular disease. Young children are especially vulnerable while their brains are still developing, but lead exposure can negatively impact people at any age, the study team notes. “Lead is able to reach the bloodstream once it’s inhaled as dust, or ingested, or consumed in water,” says the senior study author, Aaron Reuben, a clinical psychology researcher at Duke University in Durham, North Carolina. “In the bloodstream, it’s able to pass into the brain through the blood-brain barrier,” Reuben adds. Once it reaches the brain, the effects can linger for decades. A study published in 2020 in JAMA, for example, found that middle-aged adults with childhood lead exposure had significantly smaller brains with less structural integrity, conditions that may accelerate brain aging and lead to premature cognitive decline. “Millions of us are walking around with a history of lead exposure,” Reuben says. “It’s not like you got into a car accident and had a rotator cuff tear that heals and then you’re fine,” Reuben adds. “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.”
