Auxology and Environmental Epidemiology: Lead Exposure, Physical Growth and Maturation.

Abstract

The theme of this dissertation is the potential impact of pre- and post-natal lead exposure on child growth and maturation. Maternal bone lead has been inversely associated with physical growth in infants and young children, but no study has examined whether this association persists throughout preschool years. In addition, lead exposure has been implicated as a possible contributing factor to delayed puberty in cross-sectional studies. Taking advantage of a long-running birth cohort study in Mexico City that used maternal bone lead, a novel biomarker of prenatal lead exposure, we studied the association of lead with child weight trajectory from birth to 5 years, adjusting for postnatal lead exposure. Second, we identified critical windows of lead exposure susceptibility on children’s height and body mass index (BMI) at 4 years of age. Third, we examined the association of prenatal lead exposure with puberty onset among a subset of 43 girls and 31 boys at ages 6 to 15 years. Prenatal lead exposure was associated with a sustained decrease in girls’ but not boys’ weight over time, independent of postnatal lead exposure and adjusting for several confounders and predictors of child’s weight. Second, we found that the most sensitive window of lead exposure on skeletal growth during development (measured by height) was infancy (birth to 24 months). Lead exposure was not associated with children’s attained BMI at 4 years of age. Preliminary findings from the follow-up study of youth aged 6 to 15 years do not support an association of prenatal lead exposure with pubertal onset, but these findings are limited by sample size. Lead exposure at current environmental levels remains an important public health issue; it is associated with childhood weight and height deficits. Future research will investigate its association with onset of puberty in a larger sample from this cohort. The results of this research can inform future policies on the use and development of new and old pollutants.