Endocrine disruptors and thyroid function - a relationship? a systematic review about thyroid effects of endocrine disruptors.

Endocrine disruptors (EDs) are several widespread compounds, either natural or artificial, that can alter the physiological homeostasis of the natural blood born substances and which actually represent a controversial environmental topic for public health. This study is a systematic review about the relationship between EDs and thyroid dysfunctions in order to clarify the dispute or actualize the problem. PubMed and the Cochrane Library were searched systematically for English, Italian and Spanish publications on the EDs human health effect on thyroid function. All in vivo study designs were included. Two reviewers conducted the research independently, in February 2012, using the specific keywords/mesh terms. At the end of the review process we have selected 98 primary studies and 61 reviews of 1581 (and 239 reviews) initially found. 78 of them were already described in the five most recent reviews (2008-2010) about this topic; we summarize the results of these reviews and update them with the 20 studies not included in the previous reviews. Our study underlines a relationship between EDs exposure and FT3, FT4 and TSH alteration, especially for polychlorinated biphenyl, polybromophenyl ether, perchlorate, Dioxins/dioxin-like and compounds like bisphenol-A. However no study shows a significant relationship with any pathological and clinical expression of thyroid disease, mainly due to several confounding variables in the observational studies, both environmental and genetic factors. Major risk conditions are represented by pregnancy status and breast-feeding for the importance of the thyroid hormones in fetal neurodevelopment. Despite all studies underline the need of further research about this topic to settle the relationship between EDs and thyroid disease, most authors are worried about the potential health effects on several endocrine targets and in frail conditions. They recommended a precautionary and integrated approach based on primary prevention activities, through screening and health education campaigns, and the reduction or elimination of these substances as suggested by international conferences. This opens scenery of innovative collaboration between medical research, hygiene prevention and international legislation in the hope to set up in future a new dimension of the approach to many diseases.