Public Release: 6-Nov-2017
Society for Endocrinology
Pregnant women exposed to higher levels of a common environmental pollutant, perchlorate, had lower levels of a thyroid hormone crucial for normal foetal brain development, according to a study presented at the Society for Endocrinology annual conference in Harrogate. These findings suggest that exposure to this common chemical should be minimised in pregnant women to prevent potential neurodevelopmental abnormalities in children.
Perchlorate is a common environmental pollutant found in water, milk, some foods and everyday chemicals, including fertilisers and air bags. Perchlorate is known to reduce absorption of iodine from the blood into the thyroid, where iodine is needed to make the thyroid hormone, T4. Since T4 is essential for normal foetal brain development, this suggests that perchlorate exposure could decrease maternal thyroid hormone levels, which may lead to brain development defects in babies.
In order to investigate the impact of perchlorate exposure on maternal thyroid hormone levels, Professor Bijay Vaidya and his team measured the levels of perchlorate in urine samples and thyroid hormone levels in blood samples from healthy, pregnant women. The team found that higher perchlorate levels were associated with lower levels of thyroid hormones. These data were gathered in the South West of England but mirror data reported from other parts of the world.
Prof Vaidya comments, “This study adds to the growing body of evidence that exposure to the environmental pollutant, perchlorate, is widespread and may have deleterious health outcomes.”
Although further studies are required to confirm that perchlorate exposure in pregnant women can lead to impaired neurological development in offspring, these findings suggest that public health initiatives should be put in place to reduce perchlorate exposure, particularly in vulnerable populations, such as pregnant women. Furthermore, the possible health impacts of perchlorate exposure on the healthy population remain uncertain and should also be investigated.
Prof Vaidya concludes, “These findings are important because we know that optimum thyroid hormone levels during pregnancy are essential for normal foetal brain development, and this study shows that this common pollutant may be adversely affecting brain development in children.”
Perchlorate exposure affects thyroid function in third trimester pregnant women from South-West England
Bridget Knight1,2, Beverley Shields1, Elizabeth Pearce3, Lewis Braverman3, Xuemei He3, Rachel Sturley4, Bijay Vaidya5
1. NIHR Exeter Clinical Research Facility, University of Exeter Medical School, UK, Exeter, United Kingdom, 2. Royal Devon & Exeter NHS FT, R&D Department, Exeter, United Kingdom, 3Section of Endocrinology, Diabetes & Nutrition, Boston University School of Medicine, Boston, USA, 4Centre for Women’s Health, Royal Devon and Exeter Hospital NHS Foundation Trust, Exeter, United Kingdom, 5Department of Endocrinology, Royal Devon and Exeter Hospital NHS Foundation Trust, and, University of Exeter Medical School, Exeter, United Kingdom
Introduction: Iodine is important for thyroid hormone synthesis, and iodine deficiency in pregnancy may impair foetal neurological development. Perchlorate, found in some foods and everyday chemicals (e.g. fertilisers) and thiocyanate, which is found in cigarette smoke, decrease the transport of iodine from the circulation to the thyroid cells by inhibiting the sodium-iodide symporter. Environmental exposure to these substances during pregnancy may result in reduced thyroid hormone synthesis. Therefore, we aimed to explore the impact of perchlorate and thiocyanate exposure on thyroid status in a cohort of pregnant mothers from South-West England.
Methods: Urine samples were obtained from 308 women participating in a study of breech presentation in late pregnancy. They had no known thyroid disease and a singleton pregnancy at 36-38 weeks gestation. Samples were analysed for urinary concentrations of iodine (UIC), perchlorate (UPC) and thiocyanate (UTC). Blood samples were taken for free T4 (FT4), thyrotropin (TSH), thyroid peroxidase antibodies (TPO-Ab). Baseline data included: age, parity, smoking status, ethnicity, BMI at booking. Variables were assessed for normality and natural log transformed where appropriate.
Results: Participants had a mean (SD) age 31(5) years, median (IQR) BMI 24.4(22.0, 28.3) kg/m2, and median (IQR) UIC 88 (55, 158) mcg/l. 42% were primiparous, 10% were smokers, and 96% were Caucasian. Log transformed UPC was negatively correlated with FT4 in the whole cohort (n= 308, r= -0.12, p=0.03) and in the subgroup of women with UIC <100 mcg/l (n=174, r= -0.15, p=0.04). Regression analysis with the potential confounders, smoking, TPO-Ab status, UIC and UTC, identified UPC to be negatively associated with FT4 (p= 0.04). UPC was not associated with TSH, and UTC was not associated with FT4 or TSH.
Conclusion: Environmental perchlorate exposure is negatively associated with circulating FT4 levels in third trimester pregnant women. This may have an adverse impact on neurocognitive development of the fetus.?