The adverse health effects of environmental contaminants (ECs) are a rising public
health concern, and a major threat to sustainable socioeconomic development. The developing
fetuses and growing children are particularly vulnerable to the adverse effects of
ECs. However, assessing the health impact of ECs presents a major challenge, given
that multiple outcomes may arise from one exposure, multiple exposures may result
in one outcome, and the complex interactions between ECs, and between ECs, nutrients
and genetic factors, and the dynamic temporal changes in EC exposures during the life
course. Large-scale prospective birth cohort studies collecting extensive data and
specimen starting from the prenatal or pre-conception period, although costly, hold
promise as a means to more clearly quantify the health effects of ECs, and to unravel
the complex interactions between ECs, nutrients and genotypes. A number of such large-scale
studies have been launched in some developed counties. We present an overview of "why",
"what" and "how" behind these efforts with an objective to uncover major unidentified
limitations and needs. Three major limitations were identified: (1) limited data and
bio-specimens regarding early life EC exposure assessments in some birth cohort studies;
(2) heavy participant burdens in some birth cohort studies may bias participant recruitment,
and risk substantial loss to follow-up, protocol deviations limiting the quality of
data and specimens collection, with an overall potential bias towards the null effect;
(3) lack of concerted efforts in building comparable birth cohorts across countries
to take advantage of natural "experiments" (large EC exposure level differences between
countries) for more in-depth assessments of dose-response relationships, threshold
exposure levels, and positive and negative effect modifiers. Addressing these concerns
in current or future large-scale birth cohort studies may help to produce better evidence
on the health effects of ECs.