Three contaminants linked to skewed thyroid hormones in infants.

Cao, Y, BC Blount, L Valentin-Blasini, JC Bernbaum, TM Phillips and WJ Rogan. 2010. Goitrogenic anions, thyroid stimulating hormone, and thyroid hormone in infants. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.0901736.

Infants with higher exposures to three contaminants – perchlorate, nitrate or thiocyanate – found in water, food and tobacco smoke had increased levels of thyroid stimulating hormone (TSH), a sign that the thyroid gland may be underfunctioning.

The results are important because infants with poor thyroid function are at risk for stunted growth and mental impairment.

Perchlorate, nitrate and thiocyanate are environmental chemicals already associated with thyroid problems in adults. The three compounds affect thyroid function by blocking iodine uptake by the thyroid gland.  Iodine is needed to make thyroid hormone, and most of this trace mineral comes from diet.

Because perchlorate, nitrate, and thiocyanate block iodine uptake, they can create an iodine deficiency, which reduces thyroid hormone production.  Due to the link between thyroid function and mental development, children with severe dietary iodine deficiency are at risk for mental retardation.

Complicated interactions of organs and hormones control thyroid function. The brain first releases TSH as a signal to the thyroid gland – which is located in the neck – to produce and release thyroid hormone into the blood. There, thyroid hormone circulates throughout the body to regulate development and a host of other essential body functions throughout life. When thyroid hormones levels are low, TSH levels rise to stimulate thyroid hormone production. Hence, doctors consider high TSH levels to be a sign of decreased thyroid function.

People are exposed to the three contaminants from various sources. Perchlorate is used to make rocket fuel, propellants and explosives, including fireworks. It is detected in almost all human urine samples. Widespread exposure occurs through drinking water, food, breast milk and infant formula. Nitrate can be elevated in drinking water, particularly in regions with intense agriculture, high fertilizer use and confined animal feed lots. Thiocyanate is found in tobacco smoke.

In this study, researchers used samples and data gathered through the Study of Estrogen Activity and Development (SEAD). TSH, thyroid hormone, perchlorate, nitrate, thiocyanate and iodide were measured in the urine collected from 92 infants from 0 – 12 months of age. They related the contaminant levels in the urine to those of TSH and thyroid hormone. In addition, they looked to see if lower iodine levels affected the associations between the chemicals and the hormones.

They found that infants with higher amounts of any one of the three contaminants also had higher TSH in their urine.  The effect of perchlorate, in particular, was most pronounced in infants with low iodide.

Paradoxically, the authors also found that increased exposure to the three contaminants was associated with higher thyroid hormone levels. This was unexpected because high TSH levels usually accompany low thyroid hormone levels. The authors suggest that thyroid regulation may be different in infants compared to adults, and/or these contaminants may affect other aspects of thyroid and kidney function, in addition to iodine uptake.