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Background

The Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) project is a group of sequentially-enrolled, on-going, environmental epidemiologic birth cohort studies based in Mexico City. The research had the original aim of investigating the influence of cumulative maternal lead burden on various outcomes related to fetal and infant development, but the research has since expanded to include investigations related to the impacts of a wide range of environmental, nutritional, behavioral, genetic and epigenetic risk factors (as well as potential interactions between these risk factors). Similarly, the outcomes of interest have expanded to include a wide range of neurobehavioural, physical growth, cardiovascular, metabolic, endocrinologic and epigenetic outcomes.

ELEMENT’s original founders were Howard Hu and Mauricio Hernandez-Avila , who established the collaboration, built the infrastructure and initiated the research in 1993-1994 when they were at the Harvard School of Public Health and the Instituto Nactional de Salud Publica (INSP; the National Institute of Public Health of Mexico), respectively, and with initial support from the Harvard NIEHS/EPA Superfund Program (1992-2006; P01 ES005257, Project 3) and the Consejo Nacional de Ciencia y Tecnologia (CONACYT; National Foundation for Science and Technology) science foundation in Mexico. Since then, among the additional scientists who have been or are currently Principal Investigators of projects based on ELEMENT are (in alphabetical order) Adrienne Ettinger (Yale), Hector LaMadrid-Figueroa (INSP), Karen Peterson (U Michigan), Emily Somers (U Michigan), Donald Smith (U California at Santa Cruz) and Robert Wright (Harvard; transitioned in July 2012 to the Mount Sinai School of Medicine). It has received continuous support from grants from the U.S. National Institute for Environmental Health Sciences (R01 ES007821, R01 ES021446, R01 ES013744, R01 ES014930, P42 ES016454, P20 ES018171, K01 ES019909), CONACYT (CONACYT-41912-M), and other sources.

ELEMENT`s field research was and continues to be generated by a multi-disciplinary team primarily based at the INSP main campus (Cuernavaca, Morelos, Mexico), a satellite clinical research facility on the campus of the American British Cowdray Hospital (Mexico City), and offices at the Instituto Nacional de Perinatalogia (National Institute of Perinatology). The birth cohorts enrolled low to moderate income mothers either during pregnancy or at delivery from the National Institute of Perinatology, Hospital General Dr. Manuel Gea Gonzalez, and clinics affiliated with the Mexican Social Security Institute. The offspring were born beginning in 1994 through 2011 and were evaluated every 3-6 months during their first 3 years of life. Women were excluded if they planned to leave the area within 5 years; had a history of infertility, diabetes, or psychosis; consumed alcoholic beverages daily during pregnancy; were addicted to illegal drugs; were diagnosed as a high-risk pregnancy; were pregnant with multiples; or did not intend to breastfeed (Cohort 1 only). Each of the four cohorts was designed to either study the impact of lead on child development or identify interventions to reduce gestational and infancy lead exposures. Cohort 1 enrolled women at delivery between 1994 and 1995 and tested the impact of postnatal calcium supplementation (randomized trial) on maternal lead levels during lactation. Cohort 2 consisted of two observational studies that examined the relationships between periconceptional and gestational lead biomarkers in two different groups of women (Cohorts 2A, which recruited women between 1997 and 2001 before pregnancy or the 1st trimester; and Cohort 2B, which recruited women between 1999 and 2003 at delivery). Cohort 3 recruited women between 2001 and 2004 for a randomized trial designed to assess the impact of gestational calcium supplementation on lead mobilization during pregnancy. Women were enrolled either before becoming pregnant or during the 1st trimester of their pregnancy.

Although each of the Cohorts had somewhat different aims and designs (reflecting the nature of the sequential competitively awarded grants that funded them), the exposure, outcome, and covariate data from these cohorts was collected in a standardized fashion by the same group of investigators and field staff, allowing the team to pool the data and generate summary effect estimates.