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Temporal pattern in the effect of postnatal blood lead level on intellectual development of young children
L Schnaas1, S J Rothenberg, E Perroni
1Department of Developmental Neurobiology, National Institute of Perinatology, Mexico City, Mexico.
Insights
Postnatal blood lead exposure negatively impacts children's cognitive development, with effects peaking 1-3 years later. Early childhood, particularly ages 4-5, is a critical window for lead
Area of Science:
- Environmental Health
- Developmental Psychology
- Toxicology
Background:
- Prenatal and early childhood lead exposure is a significant public health concern.
- Understanding the temporal dynamics of lead's neurodevelopmental effects is crucial for intervention.
- Previous studies indicate lead exposure affects cognitive function, but the timing of these effects requires further elucidation.
Purpose of the Study:
- To investigate the temporal relationship between postnatal blood lead levels and cognitive development in children.
- To identify critical windows of vulnerability for lead's impact on cognitive function.
- To quantify the long-term effects of early lead exposure on the General Cognitive Index (GCI).
Main Methods:
- Longitudinal study of 112 children from the Mexico City Prospective Lead Study.
- Repeated measures of blood lead levels from 6 to 54 months of age.
- Assessment of General Cognitive Index (GCI) using McCarthy Scales of Children's Abilities at 6-month intervals from 36 to 60 months.
- Statistical control for relevant covariates including socioeconomic status, maternal IQ, and birth characteristics.
Main Results:
- Significant interactions were observed between early blood lead levels (6-18 and 24-36 months) and age on GCI.
- The negative association between blood lead levels and GCI became more pronounced with age until 48 months for early exposure periods.
- Lead exposure during 24-36 months showed significant negative effects on GCI at 48 and 54 months, with a maximum GCI decrease of 5.8 points per log unit increase in blood lead.
- Effects of lead exposure on GCI were most evident 1-3 years after the exposure period, with ages 4-5 appearing critical.
Conclusions:
- The impact of postnatal blood lead exposure on children's cognitive development is time-dependent, with effects manifesting and peaking years after exposure.
- Early childhood, specifically ages 4-5, represents a critical period for the neurodevelopmental consequences of lead exposure.
- These findings underscore the importance of minimizing lead exposure in early childhood to protect long-term cognitive outcomes.
Abstract:
To determine the temporal pattern of the effect of postnatal blood lead level on the General Cognitive Index (GCI) of the McCarthy Scales of Children's Abilities, we used data from 112 children of the Mexico City Prospective Lead Study with complete evaluations from 36 to 60 months of age at 6-month intervals. We measured blood lead level every 6 months from 6 to 54 months. We controlled for 5-min Apgar, birth weight, birth order, sex, socioeconomic level, maternal IQ, and maximum maternal educational level in a repeated measures ANCOVA using child blood lead level grouped by 6-18 month (geometric mean 10.1 microg/dl, range 3.5-37.0 microg/dl), 24-36 month (geometric mean 9.7 microg/dl, range 3.0-42.7 microg/dl), and 42-54 month (geometric mean 8.4 microg/dl, range 2.5-44.8 microg/dl) averages. There were significant interactions between the 6-18 month blood lead level and age with GCI as the endpoint and between 24-36 month blood lead level and age. The regression coefficient of blood lead at 6-18 months became more negative with age until 48 months, when the rate of decline moderated (linear polynomial contrast p=0. 047). The regression coefficient of blood lead at 24-36 months with CGI became more negative as well from 36 to 48 months but then started decreasing toward zero from 48 to 60 months (quadratic polynomial contrast p=0.019). Significant between-subjects lead effects on GCI were found for 24-36 month blood lead level at 48 months (p=0.021) and at 54 months (p=0.073). The greatest effect (at 48 months) was a 5.8-point GCI decrease with each natural log unit increase in blood lead. Significant between-subjects lead effects on GCI were found for 42-54 month blood lead level at 54 months (p=0. 040) and at 60 months (p=0.060). The effect of postnatal blood lead level on GCI reaches its maximum approximately 1-3 years later, and then becomes less evident. Four to five years of age appears to be a critical period for the manifestation of the earlier postnatal blood lead level effects.