"This study brings into question what are acceptable lead levels and what lead levels actually result in developmental changes in performance in school," Biehler said. "It has always been my fear of how much lead is too much and how much is OK."
The research was published May 13 in the journal Pediatrics.
For the study, McLaine's team collected data on reading-readiness scores on more than 3,400 kindergarten children in Providence, R.I., and compared them with levels of lead in the children's blood.
They found that children with lead levels between 5 mcg/dl and 9 mcg/dl were 21 percent more likely to score below the national benchmark on the reading-readiness test. Children whose lead levels were 10 mcg/dl were 56 percent more likely to score below the national benchmark.
Moreover, reading-readiness scores dropped four and a half points for children whose lead levels were 5 mcg/dl to 9 mcg/dl and dropped 10 points for those with lead levels of 10 mcg/dl, compared with children whose blood lead levels were 0.5 mcg/dl, the researchers said.
McLaine noted, however, that there is no safe level of lead exposure. "We found effects when blood levels were above 2 [mcg/dl]," she said.
This is another reason to prevent lead poisoning altogether, McLaine added.
According to the CDC, children in at least 4 million homes in the United States are being exposed to lead. Approximately half a million U.S. children between the ages of 1 and 5 have blood lead levels above 5 mcg/dl.
Most of the exposure comes from old, chipping lead-based paint, which was banned in 1978 but is still found in public housing in urban areas and in many older homes.
For more information on lead, visit the U.S. Centers for Disease Control and Prevention.
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