20th Century Lead Exposure Damaged American Mental Health

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.”