November 07, 2017
1 min read

Perchlorate exposure tied to lower thyroid hormone level in pregnant women

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Pregnant women with higher levels of exposure to the chemical perchlorate are more likely to have lower levels of free thyroxine, potentially affecting fetal brain development, according to study data presented at the Society for Endocrinology BES annual conference.

Perchlorate — a chemical found naturally in some foods and used in everyday chemicals, such as bleach and fertilizer — can decrease the transport of iodine by inhibiting the sodium-iodide symporter, resulting in reduced thyroid synthesis during pregnancy, Bridget A. Knight, PhD, a research midwife with NIHR Exeter Clinical Research Facility in Exeter, United Kingdom, and colleagues wrote in an abstract.

Knight and colleagues analyzed data from 308 pregnant women without known thyroid disease participating in a study on breech presentation in late pregnancy (mean age, 31 years; mean BMI, 24.4 kg/m²; 95% white). Researchers analyzed urinary concentrations of iodine, perchlorate and thiocyanate, and blood samples for levels of free thyroxine (FT4), thyrotropin (TSH) and thyroid peroxidase antibodies (TPO-Ab).

Within the cohort, median urinary iodine concentration was 88 mcg/L; 42% were primiparous; 10% were smokers.

Researchers found that log transferred urinary perchlorate levels were negatively associated with FT4 for the whole cohort (r = –0.12; P = .03) and for a subgroup of women with a urinary iodine concentration of 100 mcg/L or less (r = –0.15; P = .04). Results persisted after adjusting for smoking, TPO-Ab status, urinary iodine concentration and thiocyanate level, according to researchers.

Perchlorate levels were not associated with TSH, and thiocyanate levels were not associated with FT4 or TSH.

“This study adds to the growing body of evidence that exposure to the environmental pollutant, perchlorate, is widespread and may have deleterious health outcomes,” Bijay Vaidya, PhD, FRCP, of the department of endocrinology at Royal Devon and Exeter Hospital NHS Foundation Trust, United Kingdom, said in a press release. “These findings are important because we know that optimum thyroid hormone levels during pregnancy are essential for normal fetal brain development, and this study shows that this common pollutant may be adversely affecting brain development in children.” – by Regina Schaffer


Knight B, et al. OC3.1. Presented at: Society for Endocrinology BES; Nov. 6-8, 2017; Harrogate, UK.

Disclosures: Endocrine Today was unable to determine relevant financial disclosures.