Research | Children’s Health

Thyroid hormones play important roles in regulating metabolism, growth, and develop ment, especially in normal brain maturation and development (Porterfield and Hendrich 1993). They regulate the processes of neuro genesis, denditric and axonal growth, synap togenesis, and myelination (Bernal 2007). It is now recognized that even slight differences in the concentration of thyroid hormones dur ing pregnancy or after delivery may be associ ated with neurological impairment (Freire et al. 2010; Pop et al. 1999). Thyroid hor mones are also essential for children because some neurodevelopmental processes, such as myelination, are not completed until adoles cence (Rice and Barone 2000), and they are also important for the behavior and cognitive function of the young and adolescent brain (Anderson 2001). In addition, thyroid hor mone deficiency causes growth delay, preco cious puberty in both sexes, and hirsutism in females (Papi et al. 2007). There is a growing concern that environ mental toxicants may be related to thyroid impairment (Boas et al. 2009). Animal stud ies have suggested that exposure to some perfluoroalkyl acids (PFAAs), including perfluorooctanoate (PFOA, also called C8), perfluorooctane sulfonate (PFOS), and per fluorononanoic acid (PFNA), may interfere with thyroid status (Lau et al. 2007; Liu et al. 2011). There had been some concern that these apparent associations may derive from the analysis of analog free thyroxine (FT4) being affected by the presence of PFOS, as observed in rats highly exposed to PFOS (Chang et al. 2007). However, such bias has not been observed in a human population with typical U.S. serum PFOS concentrations but higher PFOA concentrations (Lopez Espinosa et al. 2011a). Published epidemiological findings are not consistent (Steenland et al. 2010), have generally focused on adults, and have been crosssectional in nature—leaving a gap in our understanding of possible PFAA effects in children. Whereas associations were reported for some PFAAs and thyroid hormones in some studies of nonoccupational exposur