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Lifestyle and Environment · Environmental Exposures

Thyroid Hormones and Moderate Exposure to Perchlorate during Pregnancy in Women in Southern California

Steinmaus C, Pearl M, Kharrazi M, Blount BC, Miller MD, Pearce EN, Valentin-Blasini L, DeLorenze G, Hoofnagle AN, Liaw J

Published June 2016 Environmental health perspectives
DOI 10.1289/ehp.1409614 PMID 26485730 PMC PMC4892913

RRM Academy Synopsis

Perchlorate is associated with lower thyroid hormone in pregnancy

Higher urinary perchlorate was associated with lower thyroid hormone levels in pregnant women. The finding comes from an observational study of 1,880 women in San Diego County. After adjustment, higher perchlorate also went with higher thyroid-stimulating hormone. The authors suggest perchlorate may affect thyroid hormone production in pregnancy.

Key Findings

  • Researchers tested leftover urine and blood from 1,880 pregnant women in San Diego County, California, between 2000–2003. Their median urinary perchlorate was roughly twice the level in the general U.S. population.
  • Among 1,476 women with mid-range urinary creatinine, each 10-fold increase in perchlorate went with lower total thyroxine (T4) (β = –0.70; 95% CI: –1.06, –0.34).
  • Perchlorate also went with lower free thyroxine (fT4) (β = –0.053; 95% CI: –0.092, –0.013).
  • After adjustment, perchlorate went with higher thyroid-stimulating hormone (TSH) on a log scale (β = 0.071; 95% CI: 0.008, 0.133).
  • Women with the most thiocyanate in urine showed a stronger total T4 link (–1.28; 95% CI: –2.04, –0.51) than women with the least (–0.41; 95% CI: –1.05, 0.24).

Interpretation

The study is an observational analysis of leftover clinic samples. Each woman had one urine sample from early pregnancy and one blood sample from mid-pregnancy, about 9 weeks apart on average. The pattern matches what is known about perchlorate: it blocks iodide from entering the thyroid. The women were a convenience sample from one county, and 69.3% were Hispanic. The authors write that, if the associations are causal, the effect may be small in most exposed people. Wide exposure could still make small effects matter across a population. They also note that unknown confounding cannot be completely excluded.

RRM Context

Earlier studies cited by the authors tie small changes in thyroid hormone during pregnancy to children's thinking skills. Restorative reproductive medicine evaluates thyroid health as part of a whole-body search for root causes. Surroundings such as water and food belong in that search.

Our editorial summary of this paper, not the article's abstract.

Abstract

Background

Findings from national surveys suggest that everyone in the United States is exposed to perchlorate. At high doses, perchlorate, thiocyanate, and nitrate inhibit iodide uptake into the thyroid and decrease thyroid hormone production. Small changes in thyroid hormones during pregnancy, including changes within normal reference ranges, have been linked to cognitive function declines in the offspring.

Objectives

We evaluated the potential effects of low environmental exposures to perchlorate on thyroid function.

Methods

Serum thyroid hormones and anti-thyroid antibodies and urinary perchlorate, thiocyanate, nitrate, and iodide concentrations were measured in 1,880 pregnant women from San Diego County, California, during 2000-2003, a period when much of the area's water supply was contaminated from an industrial plant with perchlorate at levels near the 2007 California regulatory standard of 6 μg/L. Linear regression was used to evaluate associations between urinary perchlorate and serum thyroid hormone concentrations in models adjusted for urinary creatinine and thiocyanate, maternal age and education, ethnicity, and gestational age at serum collection.

Results

The median urinary perchlorate concentration was 6.5 μg/L, about two times higher than in the general U.S.

Population

Adjusted associations were identified between increasing log10 perchlorate and decreasing total thyroxine (T4) [regression coefficient (β) = -0.70; 95% CI: -1.06, -0.34], decreasing free thyroxine (fT4) (β = -0.053; 95% CI: -0.092, -0.013), and increasing log10 thyroid-stimulating hormone (β = 0.071; 95% CI: 0.008, 0.133).

Conclusions

These results suggest that environmental perchlorate exposures may affect thyroid hormone production during pregnancy. This could have implications for public health given widespread perchlorate exposure and the importance of thyroid hormone in fetal neurodevelopment.

CITATION: Steinmaus C, Pearl M, Kharrazi M, Blount BC, Miller MD, Pearce EN, Valentin-Blasini L, DeLorenze G, Hoofnagle AN, Liaw J. 2016. Thyroid hormones and moderate exposure to perchlorate during pregnancy in women in Southern California. Environ Health Perspect 124:861-867; http://dx.doi.org/10.1289/ehp.1409614.

Topics

By this author

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Lifestyle and Environment › Environmental Exposures › Endocrine Disrupting Chemicals
Craig Steinmaus, Michelle Pearl, Martin Kharrazi, Benjamin C Blount, Mark D Miller, Elizabeth N Pearce, Liza Valentin-Blasini, Gerald DeLorenze, Andrew N Hoofnagle, Jane Liaw
C Steinmaus, M Pearl, M Kharrazi, Ben Blount, B Blount, M Miller, Liz Pearce, Beth Pearce, Betsy Pearce, E Pearce, L Valentin-Blasini, G DeLorenze, Andy Hoofnagle, Drew Hoofnagle, A Hoofnagle, J Liaw
PMID 26485730 26485730 DOI 10.1289/ehp.1409614 10.1289/ehp.1409614 Steinmaus et al. 2016, Steinmaus 2016

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