A recent study has suggested that a history of lead in petrol – going back to as early as the 1920s – could be responsible for tens of millions of mental health conditions in the United States.
The study, published in The Journal of Child Psychology and Psychiatry, estimates that about 151m mental disorder diagnoses in the US are attributable to lead, said co-author Dr Aaron Reuben. assistant professor of clinical neuropsychology at the University of Virginia.
Starting in the 1920s, cars ran on petrol that contained lead right up until the 1980s, when the government started phasing out the substance – after substantial evidence of harm over the decades, according to the US Energy Information Administration.
Leaded fuel continues to be used in some planes, race cars, and farm and marine equipment, however, reports CNN.
“The people who were exposed are not in the history books,” Reuben said. “Millions of Americans are walking around with an unknown, invisible history of lead exposure that has possibly influenced for the worse how they think, feel and behave.”
How lead impacts the body
Scientists have accumulated research over the past century showing that lead is harmful to almost every organ system, he added.
In a previous study, he and a team used data on childhood blood-lead levels, leaded fuel use, and population statistics to estimate childhood lead exposure, and found that half of the US population were exposed to adverse levels of lead early in life.
The number of people affected might be unexpected to many people, said Dr Bruce Lanphear, a population health scientist at Simon Fraser University in Canada with expertise in lead poisoning. He was not involved in the research.
“Given their caveats and limitations, I think they’ve done a thorough job of trying to estimate exposures,” he said.
One limitation, however, was that researchers did not measure all possible exposure sources, meaning that the results may actually underestimate the problem, Lanphear added.
“We have not been able to fully understand how those exposures influenced health and disease across the century,” Reuben added.
Lead is a potent neurotoxin and can disrupt brain development in many ways that can impact most types of mental health problems, including anxiety, depression and ADHD, he said. But people may have also been affected in ways that cannot be diagnosed.
“It also changed personalities. We believe that (lead exposure) makes people a little less conscientious – so less well organised, less detail-oriented, less likely to be able to pursue their goals in an organised way, and more neurotic,” Reuben added.
Millions of homes still contain lead, he added.
“We completely phased lead out of petrol in 96, out of pipes in 86, and out of paint in 78. People living in homes built before those years should be aware there is probably a lead hazard in their soil or home.”
Study details
Contribution of childhood lead exposure to psychopathology in the US population over the past 75 years
Michael J. McFarland, Aaron Reuben, Matt Hauer.
Published in The Journal of Child Psychology & Psychiatry on 4 December 2024
Abstract
Background
More than half of the current US population was exposed to adverse lead levels in childhood as a result of lead's past use in gasoline. The total contribution of childhood lead exposures to US-population mental health and personality has yet to be evaluated.
Methods
We combined serial, cross-sectional blood–lead level (BLL) data from National Health and Nutrition Examination Surveys (NHANES) with historic leaded-gasoline data to estimate US childhood BLLs from 1940 to 2015 and calculate population mental-health symptom elevations from known lead-psychopathology associations. We utilized five outcomes: (1) General Psychopathology “points”, reflecting an individual's liability to overall mental disorder, scaled to match IQ scores (M = 100, SD = 15); (2) Symptoms of Internalizing disorders (anxiety and depression) and Attention-deficit/Hyperactivity Disorder (AD/HD), both z-scored (M = 0, SD = 1); and (3) Differences in the personality traits of Neuroticism and Conscientiousness (M = 0, SD = 1).
Results
Assuming that published lead-psychopathology associations are causal and not purely correlational: We estimate that by 2015, the US population had gained 602-million General Psychopathology factor points because of exposure arising from leaded gasoline, reflecting a 0.13-standard-deviation increase in overall liability to mental illness in the population and an estimated 151 million excess mental disorders attributable to lead exposure. Investigation of specific disorder-domain symptoms identified a 0.64-standard-deviation increase in population-level Internalizing symptoms and a 0.42-standard-deviation increase in AD/HD symptoms. Population-level Neuroticism increased by 0.14 standard deviations and Conscientiousness decreased by 0.20 standard deviations. Lead-associated mental health and personality differences were most pronounced for cohorts born from 1966 through 1986 (Generation X).
Conclusions
A significant burden of mental illness symptomatology and disadvantageous personality differences can be attributed to US children's exposure to lead over the past 75 years. Lead's potential contribution to psychiatry, medicine, and children's health may be larger than previously assumed.
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