New research shows that even a low exposure to lead can result in emotional and behavioral problems in children.
As blood lead levels increase, so do the problems, according to a new study published in the journal JAMA Pediatrics.
“This research focused on lower blood lead levels than most other studies and adds more evidence that there is no safe lead level,” said Kimberly Gray, Ph.D, Health Scientist Administrator at the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health, which funded the study.
“It is important to continue to study lead exposure in children around the world, and to fully understand short-term and long-term behavioral changes across developmental milestones. It is well-documented that lead exposure lowers the IQ of children.”
For the study, researchers analyzed blood samples taken from 1,300 Chinese children between the ages of three and five. Behavioral problems were then assessed at age six using standardized questionnaires.
The researchers found that the average level of lead in the children’s blood was 6.4 micrograms per deciliter.
While most studies have examined the health effects of lead levels at or above 10 micrograms per deciliter, this study focused on lower levels, the researchers said. They note the Centers for Disease Control now uses a reference level of five micrograms per deciliter to identify children with blood lead levels that are much higher than normal.
“Young children are particularly vulnerable to the toxic effects of lead, because lead can affect children’s developing nerves and brains,” said senior author Jianghong Liu, Ph.D., from the University of Pennsylvania School of Nursing in Philadelphia.
While lead is a naturally occurring metal, lead exposure in children is often tied to human activities, including burning fossil fuels, mining, and manufacturing. In the United States, lead exposure usually comes from products that contain lead, such as paint, caulking, and pipe solder, in older homes. In China, lead exposure is more often related to air pollution, according to the research team.
“The sources of lead exposure may explain why concentrations of lead are different,” explained Liu. “In China, we found that blood lead concentrations increased with age in preschool children. In the United States, however, blood lead concentrations increase with age in children up to two to three years old and then decline.”
For this study, researchers found the increased lead concentration in the blood was linked to an increased risk of behavioral and emotional problems, such as being anxious, depressed, or aggressive.
Behavior was assessed by having the children’s teachers and parents fill out standardized questionnaires. This provided both a strength and a limitation to the study, the researchers noted.
“The study used scores from two sources, but the ratings do not provide a clinical diagnostic measure of behavioral problems,” said Liu.
The researchers also noted that U.S. studies have found that lead exposure was linked to what psychologists call externalizing behavior problems, such as aggressiveness and bullying, which may lead to truancy and even jail time as children get older.
In this study, children with higher blood lead levels had internalizing problems, such as anxiety and depression, as well as some externalizing problems. Though not addressed in this study, Liu said these differences could be explained by cultural, genetic, or environmental variations, or research gaps.
“Continuing monitoring of blood lead concentrations, as well as clinical assessments of mental behavior during regular pediatric visits, may be warranted,” the researchers concluded.