The adverse health effects of lead exposure in children are well described and include intellectual and behavioral deficits, making lead exposure an important public health problem. Lead toxicity can affect every organ system. While the immediate health effect of concern in children is typically neurological, childhood lead poisoning can lead to health effects later in life including renal effects, hypertension, reproductive problems, and developmental problems with their offspring. Even low levels of exposure have been shown to have many subtle health effects. Some researchers have suggested that lead continues to contribute significantly to socio-behavioral problems such as juvenile delinquency and violent crime.
The significant differences between the geometric mean blood lead levels (GM BLLs) by race/ethnicity and income indicate a persistent disparity. In January 2012, the CDC’s Advisory Committee on Childhood Lead Poisoning Prevention (ACCLPP) observed that these disparities can be traced to differences in housing quality, environmental conditions, nutrition, and other factors designed to control or eliminate lead exposure.
No safe blood lead level (BLL) in children has been identified. To estimate the number of children aged 1–5 years in the United States at risk for adverse health effects from lead exposure and to assess the impact of prevention efforts, the CDC analyzed data from the National Health and Nutrition Examination Survey (NHANES) from the periods 1999–2002 to 2007–2010. An estimated 535,000 U.S. children aged 1–5 years (2.6%) had BLLs ≥5 µg/dL. Despite progress in reducing BLLs among children in this age group overall, differences between the mean BLLs of different racial/ethnic and income groups persist, and work remains to be done to reach the CDC’s Healthy People 2020 objective of reducing mean BLLs for all children in the United States.
In 1991, the CDC defined BLLs ≥10 µg/dL as the "level of concern" for children aged 1–5 years. However, in May 2012, the CDC accepted the recommendations of its ACCLPP that the term "level of concern" be replaced with an upper reference interval value defined as the 97.5th percentile of BLLs in U.S. children aged 1–5 years from two consecutive cycles of NHANES.
The CDC conducts NHANES, a continuous, cross-sectional, representative survey of the noninstitutionalized U.S. civilian population, using a complex, multistage probability design. Since the mid-1970s, when NHANES first began measuring blood lead levels, the survey has become the basis for monitoring changes in BLLs in the United States. Beginning in 1999, NHANES became a continuous survey, with roughly 10,000 NHANES participants interviewed and examined during each 2-year cycle. Approximately 1,240 children aged 1–5 years are examined every cycle, and a blood specimen is drawn from approximately 850 (69%) of them. The current upper reference interval value of the 97.5th percentile of the distribution of the combined 2007–2008 and 2009–2010 cycles of NHANES was calculated as 5 µg/dL.
This analysis was focused on demographic categories with long-standing disparities in risk for high BLLs between groups: age, sex, race/ethnicity, age of housing, poverty income ratio (PIR), and Medicaid enrollment status. Race/ethnicity was categorized as non-Hispanic white, non-Hispanic black, Mexican American, and "other." Although children whose race/ethnicity was categorized as "other" were included in overall estimates, they were excluded from estimates stratified by race/ethnicity because of small numbers. PIR was calculated by dividing the total annual family income by the federal poverty threshold specific to family size, year, and state of residence. PIR was categorized as either <1.3 or ≥1.3 times the poverty level.
Disparities in the GM BLL by factors such as race/ethnicity and income level, which have been important historically, persist. The difference between the GM BLL of non-Hispanic black children (1.8 µg/dL [CI = 1.6–1.9]) compared with either non-Hispanic white (1.3 µg/dL [CI = 1.1–1.4]) or Mexican American (1.3 µg/dL [CI = 1.2–1.4]) children remains significant (p<0.01). The difference in GM BLL among children belonging to families with a PIR <1.3 compared with families with a PIR ≥1.3 also is significant (1.6 µg/dL versus 1.2 µg/dL, respectively [p<0.01]), as is the difference in GM BLL by age group and Medicaid enrollment status.
Substantial progress has been made over the past four decades in reducing the number of children with elevated BLLs. Data from the 1976–1980 cycle of NHANES indicated that an estimated 88% of children aged 1–5 years had BLLs ≥10 µg/dL. Since then, the percentage has fallen sharply, to 4.4% during 1991–1994 (NHANES III), to 1.6% during 1999–2002, and to 0.8% during 2007–2010. National estimates of the GM BLL for children aged 1–5 years declined significantly over time, from a 1976–1980 estimated GM BLL of 15 µg/dL (CI = 14.2–15.8) to a 1988–1991 estimated GM BLL 3.6 µg/dL (CI = 3.3–4.0), and this trend continues. During 1999–2002, the GM BLL was 1.9 µg/dL (CI = 1.8–2.1), compared with the 2007–2010 estimated GM BLL of 1.3 µg/dL (CI = 1.3–1.4).
The greatest reductions have occurred among children in racial/ethnic and income groups that historically were most likely to have BLLs ≥10 µg/dL. These reductions reflect the impact of strategies coordinated and implemented at national, state, and local levels. They include elimination of lead in vehicle emissions, elimination of lead paint hazards in housing, reduction in lead concentrations in air, water, and consumer products marketed to children, and identification and increased screening of populations at high risk.
The CDC concurred with its ACCLPP that primary prevention (i.e., ensuring that all homes are lead-safe and do not contribute to childhood lead exposure) is the only practical approach to preventing elevated BLLs in children. Prevention requires reducing environmental exposures from soil, dust, paint, and water, before children are exposed to these hazards. Efforts to increase awareness of lead hazards and nutritional interventions to increase iron and calcium, which can reduce lead absorption, are other key components of a successful prevention policy. Given the continued disparity in BLLs, resources should be targeted to those areas where children are most at risk. NHANES provides useful data for measuring progress towards eliminating high BLLs and ensuring that resources are targeted toward the most vulnerable children.
See the CDC Report
See the CDC Lead Site