The toxic metal lead has cast a long shadow on the well-being of all of us. A new study published Wednesday shows that lead exposure during the 20th century severely damaged the brain health of Americans, which may have helped cause some cases of mental illness that otherwise would not have occurred.
Scientists from Duke University and Florida State University conducted the study, building on their previous research on the impact of lead on our health. They estimate that childhood lead exposure—especially during the decades when it was most widely available in gasoline—directly contributed to an additional 151 million cases of mental disorders among Americans over the past 75 years. The findings indicate that lead has been more harmful to humanity than we knew.
Automakers began adding lead to gasoline in the 1920s, aiming to reduce wear and tear in engines. Leaded gasoline eventually became America’s largest source of lead exposure, peaking in the mid-1960s. But while scientists have long known that heavy lead exposure was bad for us, it was confirmed in the 1970s that even small amounts of lead can be harmful, especially to the brains of young children.
It may take decades more for lead to be fully phased out of gasoline (1996 in the US, but by 2020 for all countries in the world) and other common products, however. And scientists are still trying to quantify the subtle but meaningful health effects of the constant presence of lead on people’s lives during the 20th century, including the researchers behind this latest study.
The group’s previous study in 2022 calculated that nearly half of all Americans alive in 2015 may have been exposed to harmful levels of lead in their childhood, based on population survey data and known levels of leaded fuel consumption in the country. Furthermore, they estimate that this lead exposure has collectively lowered the IQ of Americans by 824 million points, or about 3 points per person (those born in the 1960s may have lost 6 points).
In their new study, the researchers decided to examine the mental health value of lead. They cross-reference their earlier data on lead exposure as a group of Americans with other data that estimate how much lead is needed to increase a person’s risk of various mental conditions, including schizophrenia, depression, and attention deficit hyperactivity disorder. From there, they created a proxy score for Americans’ vulnerability to mental illness, called the “common psychopathology factor”.
Overall, they estimated that lead exposure, especially during the peak of lead fuel, had added an additional 602 million points of this risk to Americans living in 2015. In all likelihood, they estimate that lead has directly contributed to more than 151 million cases of mental disorders. . Significant increases linked to lead were seen in symptoms of anxiety, depression, and ADHD.
“Childhood lead exposure has likely been a major, unappreciated contributor to mental illness in the United States over the past century,” the researchers wrote in their paper, published Wednesday. Journal of Child Psychology and Psychiatry.
Although these findings are ultimately just a measure of how harmful lead has been to our mental health, this is far from the first study to blame lead for widespread effects in humans. Some studies have found evidence that high lead levels contributed to high crime rates during the 20th century by increasing people’s propensity for violent, anti-social behavior, for example. And given that there is no truly safe level of lead exposure, the researchers say their calculations may still underestimate how bad lead is for our brains.
Environmental lead levels are thankfully much lower now than they were in the 1960s. But there are still pockets of the country where levels are higher than normal and sources that can cause large concentrations of lead exposure, such as damaged water systems (well seen during the Flint Water crisis) or older homes built before 1978. peeling paint.
According to the Centers for Disease Control and Prevention, about 2.5% of children between the ages of one and five have high levels of lead in their blood. And there are many parts of the world where lead laws are very lax. The researchers cite recent information from the UN which estimates that approximately 800 million children, a third of the world’s population, are currently exposed to high levels of lead.
Yes, and there are undoubtedly many people alive today who have suffered mental illness caused by lead that would not have happened in a better world (not to mention the families or caregivers who have been affected). So while the worst of the lead damage may pass, its impact will continue to worsen for a long time.
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