Toxic metallic lead has cast a long shadow over our collective well-being. A new study released Wednesday shows that lead exposure during the 20th century significantly worsened the brain health of Americans, likely contributing to many more cases of mental illness that would otherwise never have occurred.
Scientists from Duke University and Florida State University conducted the study, building on their past research into the impact of lead on our health. They estimated that childhood exposure to lead – particularly during the decades when it was most present in gasoline – has directly contributed to 151 million additional cases of psychiatric disorders among Americans over the past 75 years. The findings indicate that lead was even more dangerous to humanity than we thought.
Automobile manufacturers began adding lead to gasoline in the 1920s, with the goal of reducing wear and tear on engines. Leaded gasoline eventually became the leading source of lead exposure for Americans, peaking in the 1960s. But while scientists have long known that heavy exposure to lead was bad for us, in the 1970s it was firmly established that even small amounts of lead could be harmful, especially to children’s developing brains.
It will take decades before lead is completely eliminated from gasoline (1996 in the United States, but 2020 for every country in the world) and other common products, instead. And scientists are still trying to quantify the subtle but significant health effects of lead’s continued presence in people’s lives during the 20th century, including the researchers behind this latest study.
That of the team previous searches in 2022 calculated that about half of all Americans alive in 2015 were likely exposed to harmful levels of lead during their childhood, based on population survey data and known levels of leaded gasoline use in the country . Furthermore, they estimated that this lead exposure had lowered Americans’ IQ overall by 824 million points, or about 3 points per person (those born in the 1960s may have lost up to 6 points).
In their new study, the researchers set out to examine lead’s toll on mental health. They cross-referenced their previous data on Americans’ collective lead exposure with other data that estimated the amount of lead needed to increase a person’s risk of various psychiatric conditions, including schizophrenia, depression, and attention deficit hyperactivity disorder. From there, they created a proxy score of Americans’ vulnerability to mental illness, quantified as “general psychopathological factor” points.
Overall, they estimated that lead exposure, especially during the peak of leaded gasoline, had added 602 million points of this vulnerability to Americans living in 2015. More concretely, they estimated that lead directly contributed causing 151 million more cases of psychiatric disorders. . The largest lead-related increases were seen with symptoms of anxiety, depression, and ADHD.
“Childhood lead exposure has likely made a significant and underappreciated contribution to psychiatric illness in the United States over the past century,” the researchers wrote in their paper, published Wednesday in Journal of Child Psychology and Psychiatry.
While these findings are ultimately only an estimate of how harmful lead has been to our mental health, this is not the first study to blame lead for widespread effects on the population. Other research has done so found evidence that higher lead levels contributed to higher crime rates during the 20th century, increasing, for example, people’s tendency towards violent and antisocial behavior. And because there is no truly safe level of lead exposure, the researchers say their calculations may still underestimate how harmful lead was to our brains.
Fortunately, lead levels in the environment today are much lower than they were in the 1960s. But there are still pockets of the country where levels are higher than normal, as well as sources that can cause acute outbreaks of increased lead exposure, such as damaged water systems (conveniently observed during the Flint Water Crisis) or older homes built before 1978 that are starting to peel paint.
According to the Centers for Disease Control and Prevention, about 2.5 percent of children between the ages of one and five suffer from it significantly higher levels of lead in the blood. And there are many parts of the world where lead regulations are much more lax. Researchers cite recent UN data It is estimated that approximately 800 million children, one third of the world’s population, are currently exposed to high levels of lead.
Of course, there are also undoubtedly many people still alive today who have suffered from lead-induced mental illnesses that would not have occurred in a better world (not to mention families or caregivers who have also been affected). So while the worst of lead’s harm may be over, its impact will continue to loom for a long time.
