According to a recent study, childhood lead exposure in the U.S. has been linked to an estimated 151 million excess mental disorders and significant personality changes over the past 75 years.

A study published in the Journal of Child Psychology and Psychiatry evaluated the long-term impact of childhood lead exposure on mental health and personality in the U.S. population, examining data from 1940 to 2015.

Researchers used blood–lead level (BLL) data from the National Health and Nutrition Examination Surveys (NHANES) combined with historic leaded gasoline data to estimate childhood lead exposure. They calculated the population-level effects on general psychopathology, internalizing disorder symptoms, attention-deficit/hyperactivity disorder (ADHD) symptoms, and personality traits, specifically neuroticism and conscientiousness.

It was estimated that by 2015, the U.S. population had experienced a cumulative increase of 602 million General Psychopathology points, reflecting a 0.13 standard deviation rise in overall liability to mental illness.

This translated to approximately 151 million excess mental disorders attributable to childhood lead exposure. Population-level increases were also observed in internalizing symptoms (0.64 SD) and ADHD symptoms (0.42 SD). Regarding personality traits, neuroticism increased by 0.14 SD, while conscientiousness decreased by 0.20 SD.

The most affected cohorts were individuals born between 1966 and 1986, corresponding to peak exposure to leaded gasoline emissions.

The researchers concluded that childhood lead exposure significantly contributed to the burden of mental illness and disadvantageous personality changes over 75 years in the U.S., suggesting lead’s impact on public health may have been previously underestimated.

Full list of disclosures can be found in the original study.