(HealthDay News) -- Even children with low levels of lead in their blood score lower on reading-readiness tests when they begin kindergarten, a new study found.
"We now know that poorer scores on reading-readiness tests are associated with low lead levels," said researcher Patricia McLaine, director of community/public health nursing at the University of Maryland School of Nursing. "That's important, because we are very concerned about children having sufficient reading readiness when they enter kindergarten.
"For success at school, it's another indication that we need to identify children who are being exposed to lead and take action to protect them and reduce their exposure," she added.
McLaine said she believes there is no safe level of lead exposure for children. Last year, the U.S. Centers for Disease Control and Prevention lowered the blood lead level that would be considered concerning from 10 micrograms per deciliter (mcg/dl) to 5 mcg/dl. That means many more children under the age of 5 can now be diagnosed with too much lead in their blood, a condition that has been linked to developmental problems and even a lower IQ, according to the agency.
But one expert said that is not enough, particularly given the latest findings.
"This confirms that there is really no safe level of lead," said Ruth Ann Norton, executive director of the Green & Healthy Homes Initiative.
"The CDC should eliminate the term 'level of concern,' and say any level is of concern," she said.
"Clearly, zero has to be the goal," Norton said. "We have set a false guidance. We have failed more generations of kids by not aggressively moving to zero tolerance of lead poisoning."
Another expert echoed that concern.
"The idea that there is a correlation between low lead levels and reading readiness and school performance is very concerning," said Dr. Jefry Biehler, a pediatrician at Miami Children's Hospital.
"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.