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Biomedical subjects

D C Bellinger

Publications and source records attributed to D C Bellinger.

28 records · Page 2Linked to original sources
PubMed1983

Lead and the relationship between maternal and child intelligence.

Using regression analysis, we show that the IQs of children with elevated levels of dentine lead (greater than 20 parts per million) are below those expected, based on their mothers' IQs. Moreover, the amount by which a child's IQ falls short of the expected value increases with increasing levels of dentine lead in what may be a nonlinear fashion. Although lead level contributed nothing to the prediction of IQ for children with low levels of dentine lead (less than 10 parts per million), it rivaled maternal IQ in importance as a predictor in the group with elevated lead values. Thus for schoolchildren with lead burdens in the highest decile of the distribution for the urban area we sampled, the usual relationship between maternal and child IQ appears to be disrupted in a manner systematically related to lead levels in dentine.

Dentin↗
PubMedDate not supplied

Neuropsychological correlates of low-level lead exposure in school-age children: a prospective study.

The neuropsychological underpinnings of lead-associated deficits in general cognitive abilities and academic achievement were investigated in a cohort of 148 middle and upper-middle class 10 year-olds. Scores on a battery of neuropsychological tests were examined in relation to blood lead levels measured at birth and ages 6, 12, 18, 24, 57 months, and 10 years. Although numerous indices of the level, nature, and variability to children's performance on the WISC-R were associated with blood lead level measured at 24 months of age (pb24), relatively few significant associations were noted between specific measures of neuropsychological functions and pb24 (or other blood lead measurements). Some evidence was found for an association between recently measured lead levels and qualitative aspects of a child's performance (e.g. perseveration). The presence of more significant lead effects on broad-based measures of functioning than on neuropsychological tests may be attributable to the use of insensitive measures of neuropsychologic function, limitations in coverage provided by the tests, the nature of lead's CNS impact, or individual differences in biologic vulnerability to lead.

Child↗
PubMedDate not supplied

Interpreting the literature on lead and child development: the neglected role of the "experimental system".

Controversy over lead's effect on children's cognition rests in part on the assumption that if such an effect exists it can be characterized by a single estimator (e.g., the same rate of decline in IQ with increasing exposure, the same neuropsychological presentation), which will be found by any study that is valid. Accordingly, efforts to resolve inconsistencies in study findings have focused almost exclusively on data analytic issues germane to bias, in particular confounding and its statistical control. Relatively little consideration has been given to the role of effect modification, i.e., the impact on effect estimation of differences in the "experimental systems" employed in human epidemiological studies. Lack of consistency in findings could be due to differences among study cohorts in exposure/toxicokinetic factors (e.g., dose, timing), differences in environmental characteristics (e.g., co-exposures, co-morbidity, developmental supports, assessment setting), or differences in the distribution of genetic characteristics that affect lead metabolism. Recent findings regarding lead's impact on the development of nervous system structure and function are consistent with the hypothesis that contextual factors affect the form in which lead toxicity is expressed and may contribute to the failure to date to identify a lead-associated "behavioral signature." Characterizing the neuropsychological effects of lead might be facilitated by greater use of a clinical "process" approach to assessment, which would permit the type of fine-grained analyses of lead-associated performance differences often employed in studies of behavioral toxicity in animal models.

Animals↗
PubMedDate not supplied

Effect modification in epidemiologic studies of low-level neurotoxicant exposures and health outcomes.

Little attention has been invested in exploring the possibility that the nature or magnitude of a neurotoxicant's health impact on children depends on host characteristics (e.g., sex, age) or contextual factors (e.g., socioeconomic status, other chemical exposures). Such effect modification is a property of a true association, and should be distinguished from confounding. In epidemiologic studies of children, most efforts to identify effect modification have been unsystematic, pursued as part of data analysis rather than of study design. As a result, most samples have insufficient statistical power to characterize effect modification with adequate precision. This may contribute to an inconsistency in results across studies. Failure to assess effect modification adequately may also lead to invalid inferences. If the magnitude of an association between a neurotoxicant exposure and a particular end point varies across strata of a third factor, an estimate that summarizes the association across strata of this factor will be inappropriate, overestimating the association in a stratum in which the association is absent, and underestimating it in a stratum in which it is present. Until such dependencies are identified, our understanding of the mechanism(s) of a compound's neurotoxicity will remain incomplete, as will the knowledge base required to formulate public policy that adequately protects the most sensitive subgroups of the population.

Child↗
PubMedDate not supplied

Early sensory-motor development and prenatal exposure to lead.

As part of a longitudinal study of the early developmental effects of exposure to lead, we administered the Bayley Scales of Infant Development at age 6 months to infants classified into three groups based on their umbilical cord blood lead levels ("low": mean = 1.8 micrograms/dl; "mid": mean = 6.5 micrograms/dl; "high": mean = 14.6 micrograms/dl). No infant had a cord blood lead level greater than 30 micrograms/dl, the level currently regarded as the upper limit of "normal" for young children. Multiple regression analyses indicated that high cord blood levels were associated with lower covariance-adjusted scores on the Mental Development Index. Scores on the Psychomotor Development Index were not significantly related to cord blood lead level. The level of lead in blood at 6 months of age was not associated with scores on either the Mental or Psychomotor Development Index. These data are compatible with the hypothesis that low levels of lead delivered transplacentally are toxic to infants.

Child Development↗
PubMedDate not supplied

Epidemiologic approaches to assessing the developmental toxicity of lead.

A variety of designs have been employed in epidemiologic studies of the developmental morbidity associated with low-level lead exposure. Historically, cross-sectional and retrospective cohort designs have been used most frequently. Despite improvements in their methodological rigor, however, certain design features constrain the inferences such studies can support. These limitations stem from the substantial risk that children's exposure status may be misclassified due to reliance on indices with short averaging times, and an inability to identify either age-related changes in vulnerability or time-dependent aspects of the expression of toxicity (e.g., reversibility). In response to these limitations, several studies were initiated involving repeated measurements of children's lead exposure and development over periods as long as a decade. Although these prospective studies are characterized by an unusual degree of coordination among the investigators, there are differences among them as well, most notably in terms of sample characteristics and patterns of exposure. As a result, the studies should be viewed as complementary rather than simply as replicates of one another. Moreover, like all epidemiologic approaches the prospective design has its own limitations. These include the need to maintain follow-up over a long period of time, as well as the attendant risk of bias in sample attrition, and the need to distinguish developmental effects of lead from psychometric artifacts. The Boston prospective study is used to illustrate both the strengths and weaknesses of the prospective design.

Child↗