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TOPLINE:

Every 1-unit increase in blood lead levels in early childhood — even when below the “safe” threshold of 3.5 µg/dL — was associated with declines in math and reading scores from grades 2 through 11, similar to those seen at higher lead levels.

METHODOLOGY:

• Researchers used the 2021 US CDC’s revision of the blood lead reference value to ≥ 3.5 μg/dL.
• They analyzed data from birth certificates of children born in Iowa from 1989 to 2010, academic test scores from grades 2 through 11, and blood lead testing data from 1990 to 2017.
• The analysis included 305,256 children (mean age at lead testing, 1.9 years; 49% girls) and nearly 1.8 million math and reading scores to calculate the national percentile rank (NPR).
• Primary outcomes included NPR scores across grades 2 through 11, comparing children with blood lead levels < 3.5 μg/dL with those at or above this threshold.

TAKEAWAY:

• Overall, 37.7% of children had lead levels < 3.5 μg/dL.
• Among children with blood lead levels < 3.5 μg/dL, a 1-unit increase was associated with lower NPR scores in math (-0.47; 95% CI, -0.65 to -0.30) and in reading (-0.38; 95% CI, -0.56 to -0.20).
• Similarly, for lead levels at ≥ 3.5 μg/dL, every 1-unit increase was linked to a significant decline in NPR scores for math and reading.
• The trend of declining scores with increasing lead levels was persistent across grades 2 through 11; only the declines in reading scores for grades 10 and 11 were not statistically significant.

IN PRACTICE:

“The present work provides further evidence to support that there are no safe levels of lead and that there is a need to continue to reduce or eliminate lead exposure,” the authors of the study wrote.

SOURCE:

This study was led by George L. Wehby, MPH, PhD, of the Department of Health Management and Policy at the University of Iowa in Iowa City, Iowa. It was published online on May 28, 2025, in JAMA Network Open.

LIMITATIONS:

Several laboratories used the old 5 μg/dL cutoff to quantify high lead levels. Researchers lacked data on any lead-related interventions the children may have received.

DISCLOSURES:

Wehby reported receiving grants from the Gates Foundation during the conduct of this study.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.