Childhood lead exposure may trigger the development of long-term mental health problems, new research suggests.

The finding stems from a decades-long tracking of nearly 600 New Zealanders. All were born between 1972 and 1973. At that time, most gas products still contained high levels of lead. Lead exposure was assessed at age 11, followed by mental health screenings at ages 18, 21, 26, 32 and 38.

National prominence

The investigators found that nearly all of the study participants had high blood lead levels, and faced a “small” but significantly higher risk for becoming irritable, neurotic and less conscientious as they entered young adulthood and middle age.

High lead exposure was also linked to a modestly greater long-term risk for developing drug, tobacco and alcohol addiction, alongside depression, anxiety, obsessive-compulsive disorder, mania, and/or schizophrenia.

The issue of children’s exposure to lead gained national prominence again in the aftermath of the Flint, Michigan scandal, where over 100 000 people are thought to have been exposed to the toxin for years via lead pipes in the water supply.

“We have long known that lead disrupts child brain development,” said study author Aaron Reuben. He is a graduate student of clinical psychology in the department of psychology and neuroscience at Duke University. Reuben’s previous work has linked lower IQs and greater behavioural problems among children to paediatric lead exposure.

But the study authors now conclude “that early-life lead exposure in the era of leaded gasoline experienced by individuals who are currently adults may have contributed to subtle, lifelong differences in emotion and behaviour that are detectable at least up to 38 years of age”.

And that, Reuben said, “allows us to say that lead, at least in our tested population, likely has long-term consequences for mental health. That’s new.”

Some of the highest fuel lead levels on record

However, the study did not prove that high blood-lead levels caused mental health problems later in life; it only showed an association.

The study authors reported their findings online in JAMA Psychiatry.

The researchers pointed out that although lead-in-gas bans eventually came into wide effect in many parts of the world during the late 1980s and mid-1990s, in the 1970s New Zealand was home to some of the highest gas lead levels on record.

When study participants were tested at age 11, nearly all (94%) were found to have blood levels exceeding 5mcg per deciliter of blood (mcg/dL), a level that today would automatically trigger further clinical testing.

After repeated mental screenings, high paediatric lead exposure was linked to a higher risk for developing any of 11 different psychiatric disorders decades later.

These children went on to develop a variety of “difficult” personality traits family members and friends told interviewers.

Akin to childhood maltreatment

But are such children – now in their 40s and 50s – destined to have mental health issues?

Reuben said that, unfortunately, there is no intervention that can reverse the impact of decades’ old lead exposure.

“An individual’s history of exposure is thus akin to childhood maltreatment. [It’s] a risk factor for poor mental health that we can no longer modify, but which we can try to cope with or mitigate against the consequences for quality of life,” Reuben said.

“We would argue that this is a job for mental health services, to screen for dysfunction and provide treatment to improve quality of life,” he added.

Dr Jennifer Lowry is a paediatrician, toxicologist and pharmacologist who serves as chair of the American Academy of Pediatrics Council on Environmental Health. She noted the positive changes that have occurred regarding lead exposure since the study participants were first tested.

‘Canaries in the coal mine’

“It is very important to point out that few children today have such high blood levels at age 11,” she said. Lead exposure among today’s youth “can’t really be compared” to what occurred back in the 1970s and 1980s, Lowry explained.

“[But] the broader public health message is that we need to stop using our children as ‘canaries in the coal mine’,” said Lowry.

“If we, as a society, invested in preventing the exposures in the first place, we wouldn’t have to have conversations about lead and the impact on mental health, school readiness, employment successes and how to make our children the best people that they can be,” she said. “The urgency has always been there, but few people have listened.”

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