Health Letter, May 2022
By Azza AbuDagga, M.H.A., Ph.D.
Lead, a toxic heavy metal that has no smell, was ubiquitous in the U.S. environment in the early 1970s; it was commonly present in gasoline, paint, plumbing fixtures and water pipes.
Revelations about the irreversible health effects of lead, particularly among children, led to the removal of leaded gasoline, banning of lead in paint, remediation of many lead-contaminated homes and treatment of potable water supplies. Despite such progress, reduced lead toxicity remains an incomplete public-health success story, as lead exposure is still a widespread problem.
A recent research study that analyzed a large sample of clinical commercial laboratory data of blood lead levels in young U.S. children assessed the extent of lead exposure and highlighted important associations between lead exposure among these children and certain factors pertaining to their communities.
This study was, in part, supported by federal funding and was published in the December 2021 issue of the Journal of American Medical Association (JAMA) Pediatrics.
No safe blood lead level in children
Exposure to lead can seriously harm a child’s health and cause well-documented adverse effects such as damage to the brain and nervous system, delayed growth and development, learning and behavior problems, and hearing and speech problems.
Until 2012, children were identified as having a blood lead “level of concern” if their test results were 10 or more micrograms of lead per deciliter (mcg/dL). Since then, however, the Centers for Disease Control and Prevention (CDC) has determined that any detectable level of lead in children’s bodies is unsafe. This is because even low levels of lead in a child’s blood can decrease that child’s intelligence level, attention level and performance in school. Therefore, the agency has been emphasizing the importance of primary prevention efforts to avert children’s exposure to any lead in the first place.
In 2012, the CDC selected a population-based blood lead level of 5 mcg/dL as a threshold reference value to identify children who have been exposed to hazardous amounts of lead. In 2021, the agency lowered this reference value to 3.5 mcg/dL.
When children with lead exposure are identified, their sources of lead exposure should be determined and controlled or removed safely to prevent further exposure and subsequent damage.
The JAMA Pediatrics study
The study was conducted by researchers from Boston Children’s Hospital and Quest Diagnostics, a large U.S. clinical commercial laboratory that provided the study data.
The study data involved results of blood lead tests pertaining to 1,141,441 U.S. children (overall sample) who had undergone lead testing from October 2018 to February 2020. All these children were younger than six years (71% were under three years), and 51% were boys.
Although the study data included results of blood lead tests for children from all 50 U.S. states and the District of Columbia, they are not nationally representative because not all U.S. lead testing is done at this laboratory. However, the significance of the study is that it examined blood lead levels as low as 1 mcg/dL, which the study researchers classified as a “detectable” blood lead level. It also examined elevated blood lead levels, which the researchers defined as 5 mcg/dL or more, per the CDC’s 2012 blood lead reference level. Moreover, the study researchers linked childhood-lead-testing data with U.S. Census, zip code and other data to examine community-level demographic and other factors associated with blood lead level.
The researchers found that more than half of the children in the study sample (576,092 [50.5%]) had detectable blood lead levels, indicating that most children had been exposed to lead, despite decades of public policies to reduce lead poisoning. In addition, 21,172 children (1.9%) had elevated blood lead levels.
At the state level, 24 states had proportions of children with detectable blood lead levels higher than that of the total sample (50.5%). The top states with such higher proportions were Nebraska (83%), Missouri (82%), Michigan (78%), Iowa (76%) and Utah (73%).
Additionally, six states had proportions of children with elevated blood lead levels that were more than double that of the total sample (1.9%): Nebraska (6.0%), Ohio (5.2%), Pennsylvania (5.0%), Missouri (4.5%), Michigan (4.5%) and Wisconsin (4.3%).
Compared with their privately insured counterparts, children with public health insurance (Medicaid or Medicare) had nearly twice the statistical odds of having a detectable blood lead level and only slightly higher odds of having an elevated blood lead level.
More than half (57.2%) of children living in communities with the highest levels of housing built before 1950 — when some manufactures began reducing lead content in paints voluntarily — had detectable blood lead levels, compared with 42.6% of those living in communities with the lowest level of pre-1950 housing. Furthermore, children living in communities with the highest levels of pre-1950 housing had nearly fourfold higher proportions of elevated blood lead levels than those living in the lowest levels of pre-1950 housing (3.5% versus 0.9%, respectively). These differences were statistically significant.
In addition, poverty was associated with lead exposure, highlighting the impact of social disparities on this problem. Specifically, 60.2% of children living in communities with the highest levels of poverty had detectable blood lead levels, compared with only 38.8% of those living in communities with the lowest levels of poverty. Furthermore, children living in areas with the highest levels of poverty had nearly 2.5-fold higher proportions of elevated blood lead levels than those living in communities with the lowest levels of poverty (2.9% and 1.2%, respectively). These differences were statistically significant.
Finally, children living in communities with predominantly non-Hispanic and non-Latinx Black populations had statistically significant higher odds of having detectable blood lead levels than those living in communities with predominantly White populations.
Taken together, the findings of this study underscore the pressing need to eliminate all sources of lead exposure for U.S children, especially for those living in communities that are poor, have large proportions of older homes and have a predominantly non-White population, as well as children who receive public insurance.