Lead exposure in childhood may lead to increased psychiatric symptoms in adulthood, according to a longitudinal study across nearly 3 decades.
In a sample of over 1,000 children in the Dunedin Study, those with blood lead levels >10 μg/dL at age 11 years (the historical level of concern) had more mental health problems in adulthood, scoring 2.52 points higher in general psychopathology (95% CI 0.14-4.90, P=0.04), reported Aaron Reuben, MEM, of Duke University in Durham, North Carolina, and colleagues.
The current blood lead exposure level for clinical attention is 5 μg/dL, the authors explained in JAMA Psychiatry.
Eleven disorders comprised the general psychopathology score, including participant’s internalizing (depression, anxiety, phobias), externalizing (substance dependence, conduct disorders), and thought disorders (obsessive compulsive disorder, mania, psychotic symptoms), and the researchers measured these throughout adolescence and adulthood.
For every 5 μg/dL increase in blood lead level, individuals had a 1.41 point increase in internalizing and a 1.30-point increase in thought disorder, indicating that these two symptoms primarily drove the association, according to the study.
“We know lead is a neurotoxin and we know neurotoxins generally have pretty broad effects on brain health, rather than affecting a particular area of the brain or a particular cognitive function,” co-author Jonathan Schaefer, MA, also of Duke, told MedPage Today. “So if you’re exposed to something that’s capable of affecting all kinds of cognitive abilities, it stands to reason that it might also affect your emotional functioning or the way you behave as well.”
The researchers previously reported that higher blood lead levels were linked to lower IQ and socioeconomic status within the same Dunedin cohort. Other studies have tied lead exposure to depression and panic disorder, indicating that higher blood lead levels could be associated with other psychological brain outcomes as well.
Cyrus Rangan, MD, of the Children’s Hospital Los Angeles, told MedPage Today the effects of lead exposure can have a “domino effect.” If a child’s IQ is lower due to lead exposure for example, this may cause the child to fall behind in school, which could lead to behavioral problems that could later impact adult behavior.
“This is something we’ve been grappling with for decades, trying to draw more concrete correlation between childhood lead exposure and potential problems that you may develop permanently as you grow into adulthood,” Rangan told MedPage Today.
However, Rangan said one “severe limitation” in this study was that children’s blood lead levels were only measured once at age 11, which may not accurately depict how much the individuals in these cohorts were cumulatively exposed to lead across their lifespan. Still, he noted that most damage to the brain caused by lead exposure typically occurs from the ages of 0 to 6 years, when the brain is still developing.
Another limitation was that researchers used atomic absorption spectrophotometry (AAS) to measure lead exposure, a method that can lack precision in lower ranges of blood lead levels, Rangan added. The authors noted that details on the study methods were outlined in a previous report; a separate study indicated that AAS was a simpler and less expensive way to test for lead in blood.
The cohort included individuals born from April 1, 1972 to March 31, 1973 in Dunedin, New Zealand. In total, 544 individuals (53.7% male) were tested for lead exposure at age 11 years. They were then assessed for symptoms of mental disorders through in-person interviews at ages 13, 15, 18, 21, 26, and 32 years.
The sample represents the socioeconomic status of the island in New Zealand and was mostly white, with less than 7% reporting non-white ancestry. In total, 544 children had blood lead levels over 5 μg/dL measured at age 11, with a mean 11.08 μg/dL, the authors reported.
When individuals in the cohort were age 26, researchers administered questionnaires similar to the Big Five Personality Inventory to their close family or friends to inquire about aspects of their personality.
In this evaluation, those who had higher blood lead levels in their youth was tied to increased neuroticism (95% CI 0.02-0.08, P=0.02), a decrease in agreeableness (95% CI -0.18 to -0.01, P=0.03), and a decrease in conscientiousness (95% CI -0.25 to -0.03, P=0.01) in adulthood. Researchers did not find an association between blood lead levels and extroversion or openness to experience, they wrote.
“Although we found a pretty strong association between lead exposure and problematic behaviors in childhood — especially externalizing behaviors like inattention, hyperactivity, and conduct problems — when you look at adulthood, that link seems to be a lot weaker,” Schaefer said. “In adulthood, it’s less about externalizing problems like antisocial behavior and drug use and more about depression, anxiety, and psychotic symptoms.”
Additional study limitations included the fact that it focused mostly on white individuals from one geographic area who were born in the 1970s, so the results may not be generalizable to other countries. The amount of lead this cohort was exposed to is also much higher than the average level of exposure seen in developed countries today, the authors noted.
The study was supported by the National Institute on Aging, the U.K. Medical Research Council, the Jacobs Foundation, and the Avielle Foundation.
The Dunedin Multidisciplinary Health and Development Research Unit is supported by the New Zealand Health Research Council and the New Zealand Ministry of Business, Innovation, and Employment.
Schaefer disclosed no relevant relationships with industry. Reuben disclosed support from the National Institute of Environmental Health Sciences. One co-author disclosed support from the National Institute of Child Health and Human Development.