Researchers have revealed childhood exposure to lead may be linked to poor adult mental health and anti-social personality traits
Exposure to lead as a child has been linked to poor mental health in a new study released earlier this week. Links between high lead levels in teens and lower intelligence, decreased attention span, and a greater propensity to violence had previously been established. The first study of its kind examining connections between lead exposure, personality development and mental health, results suggest long-lasting effects on the brains of those exposed decades later.
Participants whose blood lead levels were higher as children were revealed to be more likely to have personality traits linked with poorer life outcomes. These included more symptoms of mental health disorders, worse physical health, trouble with relationships, and less job satisfaction.
Researchers set out to discover if childhood lead exposure may be associated with an increased risk in mental illness or difficult personality traits in adulthood. Their findings, released in JAMA Psychiatry earlier this month, reveal that the higher a person’s blood lead levels are at aged 11, the more likely they are to show signs of mental illness and difficult personality traits later in life.
While the links were modest, according to study co-author and graduate student in clinical psychology at Duke University, Jason Reuben, he emphasised the impact these results could have:
“It’s potentially important because this is a modifiable risk factor that at one point in time everyone was exposed to, and now, certain people in certain cities and countries are still exposed to.”
Reuben and colleagues from Duke University have previously revealed research showing a link between higher levels of lead in childhood, lower IQ and lower social standing in adulthood. Results from past studies in the same group have also shown a slightly increased risk for criminal behaviour. The impact of lead is thought to be comparable to other modifiable risk factors, such as abuse during childhood.
According to co-author Jonathan Schaefer, findings suggest that the effects of led can last for “quite a long time, in this case, three to four decades. Lead exposure decades ago may be harming the mental health of people today who are in their 40s and 50s.”
Those studied were born between 1972-1973 in Dunedin, New Zealand, at a time where leaded gasoline levels were amongst the highest in the world. Between the mid-1960s to late 1980s, gasoline around the world was treated with the highest levels of lead. Most adults now in their 30s-50s would have been exposed to lead fumes from car exhausts. Children today are rarely exposed to high lead levels, with the most common sources of exposure remaining older buildings with lead plumbing or paint.
Researchers measured the blood lead levels of nearly 600 participants at age 11. Of those examined, an overwhelming 94% had blood lead levels above the current cut offs that would trigger additional clinical follow-up for children today.
To put that into perspective, the average child in the US between 1976-80 had three times the level of lead in their blood compared to current standards for clinical attention. The results of study participants were around 10 times higher than you would see in American children today, according to Professor of psychiatry, paediatrics, and behavioural neuroscience, Joel Nigg.
Senior author of the study, Terrie Moffitt explained, “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.”
The longitudinal cohort study examined over 1,000 participants from New Zealand, including 579 of which were tested for lead exposure at the age of 11. Researchers followed up with participants for more than 30 years, assessing them through clinical interviews at ages 18, 21, 26, 32, and 38. Additional personality assessments were taken at ages 26, 32, and 38.
Researchers used diagnostic criteria and symptoms commonly associated with 11 psychiatric disorders to calculate a single measure of their mental health called psychopathy (or ‘p-factor’). Areas focused on included:
- Dependence on alcohol, cannabis, tobacco, or hard drugs
- Conduct disorder
- Major depression
- General anxiety disorder, fears and phobias
- Obsessive-compulsive disorder (OCD)
Results indicated that lead’s effects on mental health, as measured by individuals’ p-factor score, was about as strong as its impact on IQ.
Friends and family members of study participants were also questioned about the adult personality of their loved one. Overall, participants were described as having more difficult adult personalities, specifically being described as more neurotic, less agreeable, and less conscientious than their less-exposed peers.
While unable to prove cause and effect, researchers were able to account for a wide variety of factors that may have influenced results, such as childhood socioeconomic status.
Co-author Avshalom Caspi said, “If you’re worried about lead exposure’s impact on IQ, our study suggests you should probably also be worried about mental health.”
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