The decision to add lead to our gasoline a century ago continues to have consequences for our health, new research this week suggests. A study estimates that half of all Americans alive in 2015 were likely exposed to damaging levels of lead in their childhood, from ubiquitous sources such as leaded gasoline. This exposure could have had a subtle but lifelong effect on people’s brain health, including lower IQ and cognitive function, the researchers say.
In the 1920s, car manufacturers began to add lead to gasoline, in an effort to reduce wear and tear on car engines. At the time, it was merely the latest example of lead’s versatility, with the metal having long been used in construction, cosmetics, and paint. Lead use in gasoline reached its peak during the 1960s and 1970s.
Even before leaded gasoline was introduced, though, the harmful effects of lead poisoning were well-established. Heavy exposure is known to cause serious and sometimes fatal organ damage, including killing off brain cells. But what became clear by the 1970s is that there is no safe level of lead exposure, and that exposure to low but chronic levels of lead can still be dangerous, especially to the developing brains of children. Aside from cognitive loss, other research has suggested that lead can affect people’s behavior, and there is even some evidence that higher exposure in past decades may have increased crime rates on a national level.
Many countries, including the U.S., began to phase out lead from gasoline and other common products soon after, but it would take until the mid-1990s for leaded gasoline to be fully banned locally and up until last year for it to be banned worldwide. During those years, the authors of this new study conclude, plenty of American kids were being poisoned by lead.
The study, published Tuesday in the journal Proceedings of the National Academy of Sciences, attempts to quantify the amount of brain harm caused by childhood lead exposure in America.
To do this, they analyzed historical data on how much lead Americans were exposed to as children, based on population surveys, as well as data on levels of leaded gasoline use throughout the country over the years. Lead in gasoline becomes aerosolized and is breathed in through car exhaust, and it can also contaminate the surrounding soil and environment.
Ultimately, they concluded that just about half of the American population (170 million people) alive in 2015 likely had worrying levels of lead exposure growing up. From there, they calculated the effect that this lead exposure had on people’s cognition, using IQ as a proxy. Overall, they estimated that childhood lead exposure in the U.S. resulted in a collective drop of 824 million IQ points, or almost three points on average per person. This drop was even worse for people around in the mid-to-late 1960s; the authors estimated they may have lost up to six IQ points. Those with the highest lead levels may have lost up to seven points, they estimated.
“I frankly was shocked,” study author Michael McFarland, a sociologist at Duke University, said in a statement from the university. “And when I look at the numbers, I’m still shocked even though I’m prepared for it.”
Though much has been done to reduce the presence of lead in our environment, lead exposure remains a pressing public health issue even today. Many drinking water supplies across the U.S. continue to be laced with lead—a problem most infamously exemplified by the Flint water crisis in 2014. Worldwide, the problem is even worse, and it’s estimated that lead contamination contributed to as many as 900,000 deaths in 2019, including from causes like heart disease and strokes.
It’s likely that the ramifications of lead poisoning will follow people decades down the road as well, the researchers say. They next plan to study how lead exposure in childhood may affect people’s brains in their older years, since previous research has suggested that lead can prematurely age the brain. And they also hope to study the disproportionate effect that lead has had on different groups of Americans, such as Black children, who are still more likely to be exposed to higher lead levels growing up than others.
“Millions of us are walking around with a history of lead exposure,” said study author Aaron Reuben, a PhD candidate in clinical psychology at Duke University. “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.”