Massive Study Ties Leaded Gasoline to 150 Million Mental Health Diagnoses in U.S.

December 13, 2024

Leaded gasoline and exposure to its exhaust may help explain an estimated 151 million U.S. cases of psychiatric disorders, including ADHD, depression, and anxiety, according to a new cross-sectional study spanning the last 75 years published in the Journal of Child Psychology and Psychiatry.¹

Exposure to leaded gasoline from car exhaust was tied to population-wide cases of mental health disorders from 1940 to 2015 by researchers from Duke University, Florida State University, and the Medical University of South Carolina. They estimated that more than half of the current U.S. population was exposed to harmful levels of lead in childhood, resulting in profound effects on their mental health, personality traits, and overall well-being. People born between 1966 and 1986 (referred to as Generation X) experienced the highest rate of lead exposure and are at the greatest risk for anxiety, depression, ADHD, and personality changes.

“Research on lead as a developmental neurotoxicant is robust,” says Joel Nigg, Ph.D., a clinical psychologist and a professor in the departments of psychiatry and behavioral sciences at Oregon Health & Science University. “Its correlation with ADHD is also well established. Even low levels of exposure have an effect on ADHD.”², ³

Nigg was the principal investigator on several studies suggesting that lead exposure has a causal role in ADHD. One study published in Psychological Science found that children with ADHD who had the HFE C282Y gene mutation exhibited significantly more symptoms of hyperactivity and impulsivity than did children with ADHD who lacked the mutation.⁴

“Because the C282Y gene helps to control the effects of lead in the body, and the mutation was spread randomly in the children, it is difficult to explain these findings unless lead is, in fact, part of the cause of ADHD, not just associated with it. Numerous animal studies also support a link,” he says.

Leaded Gasoline Exposure Is a Public Health Crisis

Nigg’s study and others have linked lead exposure to life-long mental, physical, and behavioral issues; lowered IQ points; and personality changes.⁵, ⁶, ⁷, ⁸ However, the findings from the Journal of Child Psychology and Psychiatry’s study highlight the historic and pervasive effects of lead exposure on the cognitive and psychological health of a staggering slice of the U.S. population.

“Lead’s potential contribution to psychiatry, medicine, and children’s health may be larger than previously assumed,” the researchers wrote.

The study analyzed lead levels in children’s blood collected for the CDC’s National Health and Nutrition Examination Surveys (NHANES) and correlated that with historic leaded-gasoline data. The researchers calculated “mental illness points” based on the fraction of changes in the mental health of Americans born in different years and the population elevations of mental health symptoms associated with lead exposure.

The researchers identified a cumulative increase of 602 million general psychopathology points across the population, corresponding to an estimated 151 million additional mental disorders. They found that lead exposure heightened the risks for anxiety, depression, and ADHD; increased neuroticism, associated with negative emotionality; and decreased conscientiousness, reflecting less self-control and goal-oriented behavior.

While the study’s results do not prove causation, the researchers say that their findings will provide doctors with insights about their patients’ symptoms and underscore the need for expanded lead testing in patients and the recognition of lead poisoning as a neurodevelopmental disorder within a psychiatric diagnostic framework.

Leaded Gasoline Exposure: Next Steps

Lead was added to gasoline in the 1920s to improve engine performance. During the early childhood years of Generation X, leaded gasoline became the predominant fuel type in the U.S. In the mid-1970s, the U.S. Environmental Protection Agency (EPA) began phasing out leaded gasoline, but a U.S. ban did not go in effect for on-road vehicles until 1996. Lead is still found in some paints, children’s toys, and deteriorating water pipes.

According to The CDC, high levels of lead exposure can lead to seizures, vomiting, memory loss, and even death. Exposure to even small amounts of lead can be harmful. Children 6 years or younger are most vulnerable to lead poisoning, which can cause development and growth delays, hearing and speech problems, difficulty learning and paying attention, and serious illness and death.

Symptoms of lead poisoning can be hard to recognize in children. The CDC recommends discussing possible lead exposure with a child’s healthcare provider and testing children ages 1 to 5 for lead if they:

• Live in a home built before 1978
• Receive Medicaid services
• Are an immigrant, refugee, or adopted from another country
• Live near a known source of lead, such as a lead smelter or mine

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