20th century lead exposure damaged American mental health

A new study calculates that exposure to car exhaust from leaded gas during childhood altered the balance of mental health in the U.S. population, making generations of Americans more depressed, anxious and inattentive or hyperactive. The research estimates that 151 million cases of psychiatric disorder over the past 75 years have resulted from American children’s exposure to lead.

The findings, from Aaron Reuben, a postdoctoral scholar in neuropsychology at Duke University, and colleagues at Florida State University, suggest that Americans born before 1996 experienced significantly higher rates of mental health problems as a result of lead, and likely experienced changes to their personalities that would have made them less successful and resilient in life.

Leaded gas for cars was banned in the U.S. in 1996, but the researchers say that anyone born before then, and especially during the peak of its use in the 1960s and 1970s, had concerningly high lead exposures as children.

The team’s paper will appear the week of December 4 in the Journal of Child Psychology and Psychiatry.

Lead is neurotoxic and can erode brain cells and alter brain function after it enters the body. As such, there is no safe level of exposure at any point in life, health experts say. Young children are especially vulnerable to lead’s ability to impair brain development and alter brain health. Unfortunately, no matter what age, our brains are ill-equipped for keeping lead toxicity at bay.

Because water systems in older American cities still contain lead pipes, the EPA issued regulations in October that give cities 10 years to identify and replace lead plumbing, and $2.6 billion to get it done. Earlier this year the EPA also lowered the level of lead in soil that it considers to be potentially hazardous, resulting in an estimated 1 in 4 U.S. households having soil that may require cleanup.

“Humans are not adapted to be exposed to lead at the levels we have been exposed to over the past century,” Reuben said. “We have very few effective measures for dealing with lead once it is in the body, and many of us have been exposed to levels 1,000 to 10,000 times more than what is natural.”

Over the past century, lead was used in paint, pipes, solder, and, most disastrously, automotive fuel. Numerous studies have linked lead exposure to neurodevelopmental and mental health problems, particularly conduct disorder, attention-deficit / hyperactivity disorder, and depression. But until now it has not been clear how widespread lead-linked mental illness symptoms would have been.

To answer the complex question of how leaded gas use for more than 75 years may have left a permanent mark on human psychology, Reuben and his co-authors Michael McFarland and Mathew Hauer, both professors of sociology at Florida State University, turned to publicly available nationwide data.

Using historical data on U.S. childhood blood-lead levels, leaded-gas use, and population statistics, they determined the likely lifelong burden of lead exposure carried by every American alive in 2015. From this data, they estimated lead’s assault on mental health and personality by calculating “mental illness points” gained from leaded gas exposure as a proxy for its harmful impact on public health.

“This is the exact approach we have taken in the past to estimate lead’s harms for population cognitive ability and IQ,” McFarland said, noting that the research team previously identified that lead stole 824 million IQ points from the U.S. population over the past century.

“We saw very significant shifts in mental health across generations of Americans,” Hauer said. “Meaning many more people experienced psychiatric problems than would have if we had never added lead to gasoline.” Lead exposure led to greater rates of diagnosable mental disorders, like depression and anxiety, but also greater rates of individuals experiencing more mild distress that would impair their quality of life.

“For most people, the impact of lead would have been like a low-grade fever,” Reuben said. “You wouldn’t go to the hospital or seek treatment, but you would struggle just a bit more than if you didn’t have the fever.”

Lead’s effect on brain health has also been linked to changes in personality that show up at the national level. “We estimate a shift in neuroticism and conscientiousness at the population level,” McFarland said.

As of 2015, more than 170 million Americans (more than half of the U.S. population) had clinically concerning levels of lead in their blood when they were children, likely resulting in lower IQs and more mental health problems, and likely putting them at higher risk for other long-term health impairments, such as increased cardiovascular disease.

Leaded gasoline consumption rose rapidly in the early 1960s and peaked in the 1970s. As a result, Reuben and his colleagues found that essentially everyone born during those two decades were nearly certain to have been exposed to pernicious levels of lead from car exhaust. The generation with the greatest lead exposures, Generation X (1965-1980), would have seen the greatest mental health losses.

“We are coming to understand that lead exposures from the past — even decades in the past — can influence our health today,” Reuben said. “Our job moving forward will be to better understand the role lead has played in the health of our country, and to make sure we protect today’s children from new lead exposures wherever they occur.”