Researchers at Duke University focused on the effects of lead exposure during childhood on personality and mental health in adulthood. For the study, the researchers observed 579 people for decades. The participants were all born between April 1972 and April 1973. From the early 1960s to 1980s, the main contributor to lead exposure was gasoline, which comes into contact with people through automotive exhaust that was being released into the air and into the soil.
The researchers collected blood samples from the participants 11 times, starting from birth until they reached 38 years old. They analyzed those blood samples to measure heavy metals, such as lead, within the blood. The researchers found that 94 percent of the participants had lead in their bodies above 5 micrograms per deciliter of blood (mcg/dL), which is considered toxic today and needs clinical attention.
"These are historical data from an era when lead levels like these were viewed as normal in children and not dangerous, so most of our study participants were never given any treatment for lead toxicity," said Terrie Moffitt, senior author of the study.
In addition, the researchers examined the mental health and personality of the participants throughout their lives. They looked for 11 psychiatric disorders, such as alcohol dependence, cannabis dependence, tobacco dependence, drug dependence, conduct disorder, major depression, generalized anxiety disorder, fears and phobias, obsessive-compulsive disorder, mania, and schizophrenia.
Results showed that the participants who had higher levels of lead in the blood at age 11 had a higher risk of mental health problems and difficult personality traits in their adult years. The researchers concluded that higher levels of lead in a person's blood during childhood led to higher odds of exhibiting signs of mental health problems and difficult personality traits by age 38. The team published their findings in JAMA Psychiatry.
Studies reveal just how harmful lead exposure can be to children
In an earlier study, the same group of researchers found that higher levels of lead during childhood were linked to lower IQ and lower social standing later in life. Other studies revealed more serious harms that lead exposure brings to children. When children are exposed to high levels of lead, the toxic metal attacks the brain and central nervous system, resulting in coma, convulsions, and even death. Some children may survive severe lead poisoning, but they may be left with mental health problems and behavioral issues.
Blood lead exposure as low as 5 mcg/dL, which was previously thought to be a safe level, may also cause damage across multiple body systems. In particular, studies showed that lead can affect the brain development of children, leading to reduced IQ, behavioral changes like limited attention span and increased antisocial behavior, and lower educational attainment. Worse still, the neurological and behavioral effects of lead are said to be irreversible. (Related: Lead exposure linked to emotional problems, anxiety and pervasive developmental problems in children.)
Exposure to lead also results in anemia, hypertension, immunotoxicity, renal impairment, and toxicity to the reproductive organs. Studies showed that as lead exposure increases, the range and severity of symptoms and effects also increase.
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