Effects of Dioxins and Polychlorinated Biphenyls (PCBs) on Thyroid Function in Infants Born in Japan: Report from Research on Environmental Health

摘要

Dioxins (polychlorinated-dibenzo-p-dioxin (PCDD) + polychlorinated-dibenzofuran (PCDF)) and polychlorinated biphenyls (PCBs) are potentially hazardous compounds which have structural similarity to thyroid hormones. Animal studies have demonstrated that PCDDs, PCDFs and PCBs can alter thyroid hormone homeostasis. Both dioxins and PCBs are highly lipophilic and are present in large amounts in human milk samples in highly industrialized, densely populated countries such as Japan and European countries. We collected breast milk from 80 mothers (group A) living in Tokyo, Saitama, Ishikawa, and Osaka prefectures at 5, 30, 150, 300 postpartum days and measured PCDDs, PCDFs and PCBs. The mothers were limited to those aged from 25 to 34 years, and all were primiparous. Blood was taken from infants who were breast-fed at the age of one year. For evaluation of thyroid and immune function, blood was also taken from thirty infants who were bottle-fed (group B) as a control. Serum T4, T3 and FT4 levels were 10.6 ± 1.6 ug/dl, 1.6 ± 0.2 ng/ml, 1.42 ± 1.25 ng/dl in Groups A and were 11.1 ± 2.0 ug/dl, 1.7 ± 0.3 ng/ml, 1.43 ± 0.20 ng/dl in Group B respectively, and were not significantly different between the two groups. TSH levels were 2.3 ± 1.0 μU/ml and 1.8 ± 0.8 μU/ml, respectively and were within the normal range, however that of group A was significantly higher than that of group B (p=0.027). There was no correlation between serum levels of TSH, T3, T4 and FT4 and intake of dioxins. We concluded that intake of dioxins from breast milk in Japanese infants does not alter thyroid function seriously, however, the long-term effects remain to be evaluated.