Perchlorate Levels in Pregnancy Linked to Low Childhood IQ

Nancy A. Melville

October 22, 2013

SAN JUAN, Puerto Rico — Children of women with hypothyroidism and high levels of perchlorate during pregnancy have a significantly greater likelihood of having a low IQ at age 3 years, according to new research presented at the 2013 Annual Meeting of the American Thyroid Association.

"This highlights that we should be looking more at maternal perchlorate levels in studies in both children and pregnant women," said first author Peter Taylor, MD, from Cardiff University School of Medicine's Institute of Molecular and Experimental Medicine, Wales. "This is an area of research that is relatively neglected and may be almost as important as iodine status, where much more work has been done," he told Medscape Medical News.

Iodine deficiency in pregnant women has been associated with poor brain development in the offspring; since perchlorate interferes with thyroidal uptake of iodine, Dr. Taylor and his colleagues sought to investigate the effects of exposure to high levels of this ubiquitous chemical.

While the women in this study were hypothyroid, placing them at a higher risk in general, Dr. Taylor said the findings persisted even after controlling for maternal thyroid and iodine status and levothyroxine treatment, suggesting that there could be a direct action of perchlorate on the fetal thyroid.

"These results require replication in larger studies in the euthyroid pregnant population," he and his colleagues observe.

Michael McDermott, MD, director of endocrinology and diabetes practice at the University of Colorado School of Medicine, Aurora, who moderated the session in which the study was presented, said it is valuable in shedding important light on this issue.

"We are all exposed to perchlorate in the environment, with some geographic locations having much more than others. It may clearly be as important as iodine, and we should all pay more attention to this significant issue," he told Medscape Medical News.

He agreed with the authors that more work is needed to better understand the compound's effects on human growth and development. "The mechanism for the effects of perchlorate was not elucidated in this study and requires further research."

First Individual Level Look at Perchlorate and Offspring IQ

Perchlorate is made for use in rocket propellant, explosives, fireworks, and road flares and is also found at low levels in the environment; it has been found in drinking water in some areas, as well as in food and breast milk.

Dr. Taylor and colleagues evaluated a subset of 487 hypothyroid/hypothyroxinemic women participating in the Controlled Antenatal Thyroid Screening Study (CATS), in Cardiff, Wales, who had records of perchlorate levels measured in the first trimester of their pregnancy.

All women in the study showed evidence of some perchlorate exposure, with the median urine perchlorate level being 2.58 µg/L. Urine iodine levels were low, at a median of 72 µg/L.

The researchers found increased odds of offspring IQ being in the lowest 10% when maternal perchlorate levels were in the highest 10% (odds ratio, 3.14; P = .006). A greater negative impact was observed with verbal than performance IQ.

The association remained significant after adjustment for such variables as the recruitment center, maternal age, smoking, maternal thyroid and iodine status, gestational age at the time of urine or blood collection, levothyroxine treatment, the gender of offspring, and age at psychological testing.

"To my knowledge, this is the first individual level look at perchlorate in pregnancy and offspring IQ," Dr. Taylor commented.

Maternal Perchlorate Levels: "A Proxy" for Early Life?

While iodine is known to be essential for neurological development in the fetus, a recent study published in the Lancet was the first to demonstrate that even mild iodine deficiency in utero is associated with lower IQ and reading ability in children.

Dr. Taylor said the patterns of that study, which involved 1040 mothers and their offspring, also in the United Kingdom, were echoed in his research

"Via low thyroid-hormone status of the mother and/or child, interestingly, the pattern we see [with perchlorate levels] is identical to [the Lancet] iodine paper," he said. "We both see a greater impact on lower-end IQ and a greater effect on verbal than performance IQ."

The fact that the effects were almost unchanged after adjustment for levothyroxine treatment, thyroid status, and iodine levels indicates an indirect effect of maternal thyroid status, he said.

"This therefore raises the possibility that...maternal perchlorate levels were a proxy for neonatal and early life, since perchlorate is in drinking water and breast milk, and this resulted in lower thyroid function in offspring and thereby lower IQ," he said.

"However, crucially, we did not measure childhood thyroid hormone levels, so this is just speculation," he concluded.

The authors have reported no relevant financial relationships.

2013 Annual Meeting of the American Thyroid Association. Abstract 184, presented October 19, 2013.


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