RESUMO
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.
Assuntos
Desenvolvimento Infantil , Inteligência , Chumbo/sangue , Desenvolvimento Infantil/efeitos dos fármacos , Pré-Escolar , Cognição/efeitos dos fármacos , Feminino , Seguimentos , Humanos , Lactente , Inteligência/efeitos dos fármacos , Chumbo/efeitos adversos , Masculino , Gravidez , Efeitos Tardios da Exposição Pré-Natal , Testes Psicológicos , Fatores de TempoRESUMO
The authors determined the secular trend in blood lead levels in a cohort of 91 children born in Mexico City between 1987 and the beginning of 1993. The authors grouped children by calendar year in which they reached 36 mo of age (i.e., 1990-1995), and their blood lead levels were measured every 6 mo during a 66-mo period. The overall geometric mean blood lead level was 8.6 microg/dl (range = 1.0-61.0 microg/dl). A repeated measures analysis of variance revealed a significant downward linear trend in blood lead levels by year (p < .001)--from an estimated marginal geometric mean of 14.2 microg/dl in 1990 to 6.3 microg/dl in 1995. There was also a significant linear age effect (p < .001); blood lead levels generally fell during the 36th-66th mo. Family use of lead-glazed pottery significantly elevated blood lead levels (p = .006), and the effect magnified as age increased (Age x Pottery Interaction [p = .014]). Although the overall downward trend in blood lead levels during the time period described corresponded to a reduction in various sources of lead exposure, there was no alteration in production, distribution, or use of leaded pottery. Currently, use of lead-glazed ceramic pottery is one of the most profound sources of lead exposure in the Mexican population.
Assuntos
Proteção da Criança , Exposição Ambiental/análise , Chumbo/sangue , Fatores Etários , Cerâmica/efeitos adversos , Cerâmica/análise , Pré-Escolar , Estudos de Coortes , Humanos , Chumbo/efeitos adversos , Intoxicação por Chumbo/sangue , Intoxicação por Chumbo/epidemiologia , México/epidemiologia , Inquéritos e Questionários , População UrbanaRESUMO
We examined the association of maternal prenatal [range of median blood lead level 7.5-9.0 microg/dl (0.36-0.43 micromol/l) during pregnancy] and child postnatal blood lead level [range of median blood lead level from birth to 48 months 7.0-10.0 microg/dl (0.34-0.48 micromol/l)] with head circumference in from 119 to 199 children from the Mexico City Prospective Lead Study. We used repeated multiple regression modeling with a standard set of control variables, entering blood lead level last. Using Bonferroni-corrected probability values to control for inflation of Type I error due to multiple testing at each age, we found significant negative associations (p<0.05, two-tailed) between 6-month head circumference and 36-week maternal blood lead level, and 36-month head circumference and 12-month blood lead level. Over the 25-75% interquartile range of measured blood lead, head circumference decreased around 0.4 cm. Over the 1-35 microg/dl (0.05-1.68 micromol/l) range of maternal blood lead at 36 weeks, the estimated reduction in 6-month head circumference was 1.9 cm (95% CI = 0.9-3.0 cm). These results suggest that children are more vulnerable to certain effects of lead exposure at specific age ranges, and that the effect of lead on head circumference only becomes evident for brief periods in the first 4 years of life. We discuss various artifacts as well as possible mechanisms by which lead might have produced the observed pattern of results. We suggest that higher lead exposure prevalent several decades ago might have subtly influenced published normative human growth data.
Assuntos
Cabeça/crescimento & desenvolvimento , Chumbo/toxicidade , Adulto , Envelhecimento/fisiologia , Feminino , Cabeça/embriologia , Humanos , Chumbo/sangue , Modelos Estatísticos , Gravidez , Análise de RegressãoRESUMO
We determined the secular trend in blood lead levels in a cohort of 104 children born in Mexico City between 1987 and 1993. We grouped children by the calendar year in which they reached 6 mo of age and measured blood lead levels every 6 mo until they attained 36 mo of age. The overall geometric mean blood lead level was 9.6 microg/dl (range = 1.5-59.5 microg/dl). A repeated measures analysis of variance revealed a highly significant linear trend in blood lead level with year (p < .001); there was a maximum decrease of 7.6 microg/dl between 1989 and 1993. There was a highly significant quadratic age effect (p < .001); blood lead levels rose between 6 and 18 mo of age and decreased thereafter. There was a marginally significant interaction between age of the child and year. Family use of lead-glazed pottery significantly elevated blood lead levels (p = .028). The downward trend in blood lead levels during the time period of study corresponded to the reduction in various sources of lead exposure.
Assuntos
Intoxicação por Chumbo/epidemiologia , Chumbo/farmacocinética , Saúde da População Urbana/tendências , Pré-Escolar , Estudos Transversais , Exposição Ambiental/efeitos adversos , Feminino , Humanos , Incidência , Lactente , Intoxicação por Chumbo/sangue , Intoxicação por Chumbo/diagnóstico , Masculino , México/epidemiologiaRESUMO
We constructed models of umbilical cord blood lead (PbB), with and without the addition of maternal PbB at delivery and earlier in pregnancy, to determine which factors explaining cord PbB depended upon maternal PbB and which did not. We prospectively studied women of low-to-middle socioeconomic status who lived in the Valley of Mexico from 12 weeks of pregnancy to delivery. We measured maternal venous PbB during pregnancy and at delivery, and umbilical cord PbB (1-38 micrograms/dl, 0.05-1.83 mumol/l). We used multiple regression analyses to model cord PbB and a logit analysis to model the maternal-cord PbB relationship. Older mothers using lead-glazed pottery and canned foods delivered babies with increased cord PbB, while those with occasional alcohol use during pregnancy, high milk intake, and more spontaneous abortions delivered babies with lower cord PbB. Maternal PbB at 36 weeks of pregnancy and at delivery independently explained additional variance in cord PbB, but maternal PbB earlier in pregnancy did not. Some of the effects of lead-glazed pottery, maternal abortions, alcohol use, and canned food use on cord PbB were mediated through maternal PbB. The effects of maternal age and milk intake on cord PbB were independent of their influence on maternal PbB near delivery. Cord PbBs were higher than maternal PbBs at delivery in 33% of the cases, and were predominant in mothers over 30 and those drinking milk less than once per day. Measurable influence of maternal PbB on delivery cord PbB is limited to the four to eight weeks prior to delivery. Many factors suspected of influencing bone lead also control cord PbB, some of them independently of their effect on maternal delivery PbB. Minimizing fetal exposure near the end of pregnancy may require long-term control of maternal lead exposure and good management of pregnancy and diet.
Assuntos
Chumbo/sangue , Exposição Materna , Cordão Umbilical/irrigação sanguínea , Adolescente , Adulto , Cerâmica/efeitos adversos , Intervalos de Confiança , Exposição Ambiental , Comportamento Alimentar , Feminino , Humanos , Recém-Nascido , Chumbo/efeitos adversos , Modelos Logísticos , Análise por Pareamento , Idade Materna , Exposição Materna/estatística & dados numéricos , Troca Materno-Fetal , México/epidemiologia , Razão de Chances , Gravidez , Estudos ProspectivosRESUMO
The first step in modeling lead kinetics during pregnancy includes a description of sequential maternal blood lead (PbB) during pregnancy and the factors controlling it. We analyzed PbB of 105 women living in the Valley of Mexico from week 12 to week 36 of pregnancy and again at parturition. We also used data from all women contributing blood at any stage of pregnancy to determine antecedents of PbB. Pregnancies were uneventful, and offspring were normal. Although geometric mean PbB level averaged around 7.0 micrograms/dl (0.34 mumol/l), with a range of 1.0-35.5 micrograms/dl throughout pregnancy, analysis of variance revealed a significant decrease in mean PbB from week 12 to week 20 (1.1 micrograms/dl) and various significant increases in mean PbB from week 20 to parturition (1.6 micrograms/dl). Regression analyses confirmed the positive linear PbB trend from 20 weeks to parturition and additional contributions of dietary calcium, reproductive history, lifetime residence of Mexico City, coffee drinking, and use of indigenous lead-glazed pottery. Although decreasing hematocrit has been suggested to explain first-half pregnancy PbB decrease, the time course of hematocrit decrease in the present study did not match the sequential changes in PbB. While hemodilution and organ growth in the first half of pregnancy may account for much of the PbB decrease seen between 12 and 20 weeks, the remaining hemodilution and accelerated organ growth of the last half of pregnancy do not predict the trend toward increasing maternal PbB concentration from 20 weeks to delivery. Mobilization of bone lead, increased gut absorption, and increased retention of lead may explain part of the upward PbB trend in the second half of pregnancy. Reduction of lifetime lead exposure may be required to decrease risk of fetal exposure.