Lead in children's blood may be linked to increased emotional and behavioural problems such as being anxious, depressed or aggressive, new research has warned.
Emotional and behavioural problems show up even with low exposure to lead, and as blood lead levels increase in children, so do the problems, researchers said.
"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 health scientist at the National Institute of Environmental Health Sciences (NIEHS).
Blood lead concentrations measured in more than 1,300 preschool children in China were associated with increased risk of behavioural and emotional problems, such as being anxious, depressed, or aggressive. The average blood lead level in the children was 6.4 micro-grams per decilitre.
While many studies to date have examined health effects at or above 10 micro-grams per decilitre, this study focused on lower levels.
"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, from the University of Pennsylvania School of Nursing, Philadelphia.
Lead is a naturally occurring toxic metal, but sources of lead exposure are often due to human activities, including burning fossil fuels, mining, and manufacturing.
The researchers analysed one blood sample taken from each child between the ages of 3-5. Behavioural problems were assessed at age 6 using standardised questionnaires.
The questionnaires were filled out by the children's teachers and parents, which the authors noted is both a strength and limitation.
US studies reported that lead exposure causes what psychologists call externalising behaviour 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 internalising problems, such as anxiety and depression, as well as some externalising problems.
Liu said these differences could be explained by cultural, genetic, or environmental variations, or research gaps.
The finding was published in the journal JAMA Pediatrics.
