Damage from childhood lead exposure lasts well into adulthood, according to a four-decade study that found that kids who were exposed to high levels of leaded gasoline in the 1970s had worse cognitive functioning and lower socioeconomic statuses at age 38 than their peers.
“It actually wasn’t until the 1990s that the connection between lead and compromised cognitive functioning became an accepted and evidence-based ‘fact,’” Avshalom Caspi, co-author of the study and professor of psychology and neuroscience at Duke University, told The Huffington Post.
“It’s important to remember that what we think we ‘know’ about lead today is actually pretty new knowledge,” Caspi added.
The study, which examined 500 primarily white children who were born in Dunedin, New Zealand, between 1972 and 1973, was published in the Journal of the American Medical Association on March 28.
Study participants who had blood lead levels greater than 10 micrograms per deciliter at age 11 had IQs that were 4.25 points lower than their peers by the time they reached age 38.
The U.S. Centers for Disease Control and Prevention recommends public health intervention for kids with 5 micrograms per deciliter of lead in their blood or more, noting there is no safe blood lead level for children. Lead exposure is far more damaging for children because their brains are still developing.
Exposure to high levels of lead in childhood can cause neurological damage, a shortened attention span, dyslexia, attention deficit disorder, hypertension and reproductive organ damage, according the World Health Organization.
“Among those with elevated lead levels, the trend was the opposite. The occupations they held at age 38 tended to be slightly less well-paid or prestigious than their parents had.”
Few sizable studies have examined the long-term health effects of high lead exposure in kids. (To the study authors’ knowledge, the longest-term cognitive follow-up study only had 43 participants, which is too small a cohort to draw definitive conclusions from.)
“The difficulty with many previous studies of lead exposure and cognitive development is that lead exposure is often confined to very poor and very disadvantaged neighborhoods and homes,” Caspi said. “This makes it difficult to disentangle the association between high lead and low IQ from that between poverty and low IQ.”
In the U.S., poorer people were more likely to live near expressways and lead-related industries, since those neighborhoods were generally considered less desirable ― and as a result, they were more likely to be exposed to leaded gasoline. In this particular part of New Zealand, however, there were no major roadways (the area’s topography and proximity to the ocean may have kept air pollution in), meaning kids of varying backgrounds had similar exposure.
“In essence, there was equality in lead exposure,” Caspi said. “This made it possible for us to more clearly estimate the association between high lead and low IQ.”
The resulting research suggests that higher childhood blood lead levels are associated with lower IQs and with downward social mobility, regardless of a child’s socioeconomic status.
“The normal trend for this generation is for sons and daughters to achieve better occupations than their parents,” Caspi said. “Among those with elevated lead levels, the trend was opposite. The occupations they held at age 38 tended to be slightly less well-paid or prestigious than their parents had.”
During the study period, New Zealand had one of the highest lead gasoline levels in the world, the study authors noted. And although lead was phased out of gasoline in New Zealand and the United States, soil surrounding major roadways is still a hazard.
There are a few things that politicians and public health experts in the United States can learn from the new study ― particularly in Flint, Michigan, where children were poisoned by lead-tainted water starting in 2014. Caspi said he didn’t know the magnitude or the duration of Flint citizens’ lead exposure, but offered a few takeaways.
“With those routine exposures, we find that there are long-term implications for a child’s life trajectory, regardless of where they start out in life,” he said.
“To us, this suggests, at the very least, that public responses to lead exposure events, like those that we saw in Flint, should take a long-term perspective.”
While lead poisoning is essentially irreversible, proper nutrition and early intervention by doctors can improve children’s long-term cognitive outcomes, according to Dr. Mona Hanna-Attisha, the director of the pediatric residency program at the Hurley Medical Center in Flint, Michigan. Parents’ primary concern, however, should be eliminating their children’s exposure to the lead source.