Child thyroid disruption by environmental chemicals.

Laboratory experiments and animal evidences support the fact that thyroid function can be altered by a large number of chemicals routinely found in the environment and in samples of human and wildlife tissues. Although humans are commonly exposed to low pollutant doses, disrupting effects on endocrine function (e.g. thyroid) from such chemical exposures represent major health concerns. Thyroid is essential for mammalian brain development both before and after birth, and recent clinical evidences strongly suggest that brain development is much more sensitive to thyroid hormone excess or deficit than previously believed. Thyroid hormone deficit or excess during development can have permanent, pervasive and profound effects on the neurological function of the child. In addiction, maternal thyroid hormones play a role in fetal brain development before the onset of fetal thyroid function, and thyroid hormone deficit in pregnant women can produce irreversible neurological effects in their offspring. Considering that thyroid hormones are important in fetal brain development and child neurological outcome, environmental factors affecting maternal/fetal/infant thyroid function, or thyroid hormone action directly, may affect fetal brain development and child neurological outcome. The aim of this paper is to discuss how environmental chemicals can interfere with the normal production, metabolism, and excretion of thyroid hormones, and their known impact on the thyroid system during child development.