Low Levels of Lead Linked to Problems in Children

Lead is a naturally occurring toxic metal. Low blood levels of lead have been linked to low IQ, decreased academic achievement, and increased emotional and behavioral problems as well as delayed physical development in adolescents. Children are often exposed to lead because of human activities, including burning fossil fuels, mining, and manufacturing. In the United States, lead exposure usually comes from lead-containing products, such as paint and caulking in older homes. In China, lead exposure is more often related to air pollution.

Many studies have examined the health effects of lead—particularly on IQ and physical development—at or above 10 micrograms per deciliter (µg/dL) of blood. Until recently, the U.S. Centers for Disease Control and Prevention (CDC) identified that level in children as a “level of concern.” CDC now advises that children with more than 5 µg/dL of lead in their blood be considered at risk—and that action be initiated, such as reducing sources of lead in the environment.

The effects of low blood lead levels, particularly on childhood behavior and emotional problems, aren’t well understood. A research team headed by Dr. Jianghong Liu at the University of Pennsylvania and collaborators in China sought to explore these associations. Their study was funded in part by NIH’s National Institute of Environmental Health Sciences (NIEHS).

The scientists used data collected from more than 1,300 preschool age children in the Jiangsu province in China. A blood sample was taken from each child for lead testing between the ages of 3 and 5 years. Behavioral problems were assessed at age 6, during the last month of preschool, by both parents and teachers. Social and economic variables were also reported by parents. The results appeared online on June 30, 2014, in JAMA Pediatrics.

The average blood lead level in the children was 6.4 µg/dL. The researchers found higher average blood lead levels in boys than in girls. The higher the blood lead levels, the more emotional, anxiety, and behavioral problems the children exhibited. Even a small increase in blood lead concentrations of 1 µg/dL was associated with significant increases in teacher-reported emotional and anxiety problems. Girls were more likely to have internalizing problems such as anxiety and depression, and boys were more likely to have externalizing problems, such as attention and conduct issues.

“This research focused on lower blood lead levels than most other studies and adds more evidence that there is no safe lead level,” says Dr. Kimberly Gray of NIEHS.

“Young children are particularly vulnerable to the toxic effects of lead, because lead can affect children's developing nerves and brains,” Liu adds. The researchers suggest that continued monitoring of blood lead concentrations during regular pediatric visits may be warranted.