Urinary perchlorate and thyroid hormone levels in adolescent and adult men and women living in the United States

BACKGROUND: Perchlorate is commonly found in the environment and known to inhibit thyroid function at high doses. Assessing the potential effect of low-level exposure to Perchlorate on thyroid function is an area of ongoing research. OBJECTIVES: We evaluated the potential relationship between urinary levels of Perchlorate and serum levels of thyroid stimulating hormone (TSH) and total thyroxine (T-4) in 2,299 men and women, 2, 12 years of age, participating in the National Health and Nutrition Examination Survey (NHANES) during 2001-2002. METHODS: We used multiple regression models of T-4 and TSH that included Perchlorate and covariates known to be or likely to be associated with T-4 or TSH levels: age, race/ethnicity, body mass index, estrogen use, menopausal status, pregnancy status, premenarche status, serum C-reactive protein, serum albumin, serum cotinine, hours of fasting, urinary thiocyanate, urinary nitrate, and selected medication groups. RESULTS: Perchlorate was not a significant predictor of T-4 or TSH levels in men. For women overall, Perchlorate was a significant predictor of both T-4 and TSH. For women with urinary iodine < 100 mu g/L, Perchlorate was a significant negative predictor of T-4 (p < 0.0001) and a positive predictor of TSH (p = 0.001). For women with urinary iodine 2: 100 mu g/L, Perchlorate was a significant positive predictor of TSH (p = 0.025) but not T-4 (p = 0.550). CONCLUSIONS: These associations of Perchlorate with T-4 and TSH are coherent in direction and independent of other variables known to affect thyroid function, but are present at Perchlorate exposure levels that were unanticipated based on previous studies.