Dioxin effects on neonatal and infant thyroid function: routes of perinatal exposure, mechanisms of action and evidence from epidemiology studies.
OBJECTIVE
Animal experiments suggest that thyroid function alterations in newborns and infants may represent one of the most sensitive markers of toxicity from 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Dioxin can be transferred from the mother to the offspring either in utero or through lactation. It has been suggested that thyroid-hormone alterations produced by dioxin in utero or shortly after birth may underlie long-term effects, such as cognitive-ability and neurodevelopment impairment. In the present review article, we appraise available evidence on the effects of perinatal exposure to dioxin on fetal and infant thyroid function.


METHODS
We summarized the routes of perinatal dioxin exposure and research results on possible mechanisms of dioxin toxic effects on thyroid function. We performed a systematic review of epidemiology studies conducted on mother-child pairs exposed to background environmental levels to investigate dioxin effects on neonatal and infant thyroid function.


RESULTS
Toxicological and mechanistic data indicate that dioxin may impair thyroid function in exposed newborns and infants. Investigations on background-exposed children have not consistently demonstrated an association between perinatal TCDD exposure and thyroid function, although some of the studies suggest that sub-clinical hypothyroidism may be induced by perinatal dioxin exposure within 3 months from birth. Between studies inconsistencies may be related to lab method differences, mixed exposures, and small sample size of the populations evaluated.


CONCLUSIONS
Epidemiology studies have as yet failed to demonstrate an association between perinatal TCDD exposure and thyroid function alterations in human subjects, although suggestive evidence from animal and in-vitro experimental data is available.
Giacomini
Sara Mariasole
SM
EPOCA Epidemiology Research Center, Department of Environmental and Occupational Health Clinica del Lavoro L. Devoto, Maggiore Hospital Foundation IRCCS, University of Milan, via San Barnaba 8, 20122, Milan, Italy.
Hou
Lifang
L
Bertazzi
Pier Alberto
PA
Baccarelli
Andrea
A
D004147:Dioxins / Q000737:chemistry / Q000493:pharmacokinetics* / Q000506:poisoning*; D019317:Evidence-Based Medicine; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D018445:Infectious Disease Transmission, Vertical; D013961:Thyroid Gland / Q000503:physiopathology*
D004147:Dioxins