Effects of dioxins and polychlorinated biphenyls (PCBs) on thyroid function in infants born in Japan - the second report from research on environmental health

Dioxins (PCDD + PCDF) and polychlorinated biphenyl (PCB) are potentially ha zardous compounds and have structural similarity to thyroid hormones. Our r esearch group on "Dioxins and PCB in Human Milk" was organized in 1997 and has been active for the past three years. We collected breast milk from 80 mothers living in Tokyo, Saitama, Ishikawa and Osaka Prefecture in Japan at 5, 30, 150, 300 postpartum days and measured PCDDs, PCDFs and PCBs during 1998-1999. We added another 20 prefectures and cities during 1999-2000. Bre ast milk was obtained from 415 mothers at 30 postpartum days (breast-feedin g group). Blood was taken from infants who were breast-fed at the age of I year for evaluation of thyroid and immune functions. Blood was also taken f rom 53 infants who were bottle-fed (bottle-feeding group) as a control. Ser um T4, T3, FT4 and TSH levels in the breast-feeding (n = 337) and bottle-fe eding (n = 53) groups were within normal ranges and were not significantly different between the two groups. Although there were a large geographic di fferences of dioxins and co-PCB content in breast milk, there were no diffe rences in serum T4, T3, FT4, TSH levels and no significant correlation betw een the mean serum levels of TSH and TEQ in breast milk. There was a signif icant correlation between serum TSH at I year of age and that from blood on dried filter paper TSH at 5 days of age. We concluded that dioxin intake f rom breast milk in Japanese infants did not impair thyroid function. Howeve r, long-term effects remain to be evaluated. (C) 2001 Elsevier Science Ltd. All rights reserved.