Young children exposed to lead — even at low levels — are at risk for not meeting reading readiness benchmarks in kindergarten, a large study of urban children found.
On tests of reading readiness, children with blood lead levels between 5 and 9 mcg/dL scored 4.5 points (95% CI −2.9 to −6.2) lower than those with levels below 5 mcg/dL, according to Pat McLaine, DPH, of the University of Maryland in Baltimore, and colleagues.
And those with lead levels of 10 mcg/dL and higher had scores 10.1 points (95% CI −7 to −13.3) lower, the researchers reported online in Pediatrics.
Almost 25 years ago the CDC established 10 mcg/dL as a «level of concern» for blood lead levels in children, and more recently determined that children whose levels are 5 mcg/dL should be targeted for intervention.
«Learning to read is critical to the entire process of formal education,» McLaine and colleagues stated.
This requires «proficiency in phonologic processing skills (using the sounds of one’s language to process written and oral language) and in the ability to decode new words,» they explained.
A possible association between lead exposure and reading readiness has not previously been examined, but cooperation between school and public health authorities in Providence, R.I., provided an opportunity to consider this.
Using linked data from the Rhode Island Department of Health and Providence’s public school district records, McLaine’s group compared results among 3,406 children who had been tested for blood lead levels an average of three times before entering kindergarten.
Reading readiness was assessed on the Phonological Awareness Literacy Screening-Kindergarten (PALS-K) instrument, which measures reading-relevant cognitive abilities.
The test is given in the fall of kindergarten, and children who score lower than 28 out of a total of 102 are given additional classroom instruction throughout the year, the researchers explained.
The goal is for children to score 81 or higher by the time the test is repeated in the spring.
The study population was diverse and largely low income, with almost 60% being Hispanic and more than 90% qualifying for federal school lunch assistance.
The median blood level of lead in the entire group was 4.2 mcg/dL.
One in five children had had at least one blood level reading of 10 mcg/dL or higher, and more than two-thirds had at least one level of 5 mcg/dL or above.
«These results are markedly higher than [National Health and Nutrition Examination Survey] estimates from the same time and suggest that national population estimates may seriously underestimate the lead problem in urban schools,» the researchers observed.
The highest levels were seen in blacks and children whose first language was not English or Spanish, such as those of Asian descent.
About 35% of the children tested below the cutoff score on the PALS-K in the fall. These low scores were most commonly among boys, Hispanics, those receiving free lunches, and those with blood lead levels of 10 mcg/dL or higher.
Low scores also were seen in children whose mothers hadn’t completed high school or had public insurance at birth.
More than two-thirds of children whose blood levels were below 5 mcg/dL passed the cutoff PALS-K score, compared with only half of those whose levels exceeded 10 mcg/dL.
The prevalence ratio for not meeting the PALS-K benchmark score on the fall test was 1.21 (95% CI 1.19 to 1.23) among children whose blood lead levels fell between 5 and 9 mcg/dL and 1.56 (95% CI 1.51 to 1.60) for those with levels of 10 mcg/dL or higher.
This analysis found a «clear dose-response relationship» between early-life lead exposure and kindergarten reading readiness, even after adjustment for socioeconomic status, language spoken, and other demographic factors.
«Our results suggest the need to evaluate current screening approaches for early reading intervention and to determine whether adding a history of elevated [blood lead levels] could improve targeting of children who are at risk of school failure and are not presently being captured in that system,» the researchers stated.
They plan to follow these children during elementary school «to better understand the long-term impacts of both kindergarten reading readiness and childhood lead exposure on school success.»
These findings offer a caution about children who are exposed to fairly low levels of lead, according to Kevin Chatham-Stephens, MD, of Mount Sinai Medical Center in New York, who was not involved in the study.
«This study reinforces the fact that levels we used to think were safe — up to 5 mcg/dL — actually can impact children’s growth and neurodevelopment,» Chatham-Stephens toldMedPage Today.
Limitations of the study included unclear reliability of measures of lead levels and possible residual confounding.
The study was supported by the National Institute for Occupational Safety and Health Education and Research Center for Occupational Safety and Health, the CDC, and the U.S. Department of Health and Human Services.
The authors reported no financial conflicts.
Primary source: Pediatrics
Source reference: McLaine P, et al. «Elevated blood lead levels and reading readiness at the start of kindergarten» Pediatrics 2013; DOI: 10.1542/peds.2012-2277 .