Being exposed to high levels of lead as a child can cause health consequences that last well into adulthood, according to a new study published in the Journal of the American Medical Association—including a lower IQ.
Researchers followed 565 people in New Zealand who were part of a study of people born between 1972 and 1973. Each person had their blood lead levels measured when they were 11 years old, and the researchers followed up with blood tests about decades later, when they were 38.
Being exposed to lead during childhood was linked to a lower IQ in adulthood. The researchers also found that children with high blood lead levels at age 11 reached lower levels of socioeconomic status, compared to their peers with low blood lead levels in childhood. The researchers estimate that the decline in IQ accounted for 40% of that link.
There is no safe level blood lead level in children, according to the U.S. Centers for Disease Control and Prevention (CDC), but experts use the reference level of 5 μg/dL as a way to identify kids with blood lead levels that are higher than average. In the new study, the researchers reported that each 5-μg/dL increase in blood lead levels at age 11 was linked to a 1.6-point lower IQ score in adulthood. A blood lead level higher than 10 μg/dL was linked to a 2.7-point decline in adult IQ.
The United States has laws in place to limit the bad health effects caused by lead by eliminating its use in products like paint, yet exposure remains a health threat to Americans’ health, exemplified by the crisis in Flint, Michigan. The problem is widespread: a 2016 report by Reuters identified 3,000 other communities in the U.S. that recently recorded lead poisoning rates substantially higher than what was reported in Flint during the height of the crisis. Overall, the CDC estimates that about half a million children in the U.S. from ages 1-5 have blood lead levels above 5-μg/dL.
“Problems such as those in Flint are almost certain to occur periodically” until steps are taken, writes David Bellinger, a researcher at Boston Children’s Hospital, in an editorial published alongside the new study. “Children will continue to experience the greatest harm from lead exposure, and disadvantaged children will bear a disproportionate share of the burden.”
Bellinger recommends several steps be taken to reduce the consequences from lead exposure, including the continued phasing out of nonessential uses of lead, broad screening to identify kids with high levels of lead exposure and screening environments for potential exposure risks.