Lead is a well-known environmental risk for children. Too much exposure to lead can have long-term effects on a child's brain. And it may not take much lead to have an effect.
A recent study found that even small blood lead level amounts appear to influence a child's reading abilities in kindergarten.
Children with blood lead level amounts above 5 µg/dL had lower average scores on the kindergarten reading tests. They were also more likely to fail to reach the benchmark scores.
The study, led by Pat McLaine, DrPH, MPH, of the Department of Family and Community Health at the University of Maryland School of Nursing, looked at trends of reading ability in children based on their exposure to lead.
The researchers collected the reading test scores of 3,406 kindergartners, 59 percent of whom were Hispanic.
Using the state health department's records, the researchers looked at each child's blood levels of lead, averaging the amount if there were multiple tests.
Then the researchers compared the reading test scores to the children's blood lead levels, making adjustments to account for the children's sex, age, race/ethnicity, language, the year they enrolled in school and socioeconomic level, based on whether the child received a free or reduced lunch.
The overall average of blood lead levels found among the children was 4.2 µg/dL (micrograms per deciliter).
Twenty percent of the children had at least one blood draw with levels of 10 µg/dL or higher. These children were about 56 percent more likely to fail the minimum benchmark for reading readiness on the reading tests when compared to children with blood lead levels under 5 µg/dL.
Children with blood levels between 5 and 9 µg/dL were 21 percent more likely to fail to achieve the minimum benchmark scores, compared to children with blood lead levels below 5 µg/dL.
In terms of actual points on the test, the children with blood lead levels of at least 10 µg/dL scored an average 10 points lower on the reading tests than the children with levels under 5 µg/DL. The test scores range from 1 to 102.
Children with levels between 5 and 9 µg/dL scored an average 4.5 points lower than the children with levels below 5 µg/DL.
Currently, 10 µg/dL for blood lead levels has been designated the "level of concern" by the US Centers for Disease Control and Prevention. This study, however, suggests that effects on a child's cognitive skills from lead exposure may exist for blood levels below that amount, the researchers said.
Children with a blood lead level of 5 µg/dL or higher have levels higher than 97.5 percent of the rest of children their age.
The study was published May 13 in the journal Pediatrics. The research was funded by the National Institute for Occupational Safety and Health Education and Research Center for Occupational Safety and Health at the Johns Hopkins Bloomberg School of Public Health and by the Centers for Disease Control and Prevention. The authors declared no conflicts of interest.