A recent article in the Journal of Occupational and Environmental Medicine analyzes data from an earlier study in an attempt to show that in some cases of perchlorate exposure, some infants had greater odds of increased levels of Thyroid Stimulating Hormone or TSH when measured in the first 24 hours. While this in itself is not considered an adverse effect, it is also a well documented scientific fact that the first 24 hours after birth is a period of natural “TSH surge.” This makes the study’s conclusions highly suspect.
The study, “Perchlorate in Drinking Water During Pregnancy and Neonatal Thyroid Hormone Levels in California” states as its objective, “To evaluate associations between maternal drinking water perchlorate exposure during pregnancy and newborn thyroid hormone levels.”
Infants were classified as to whether their mothers lived in a community with “estimated average perchlorate” ≤ 5 or > 6 parts per billion (ppb) in drinking water. They calculated Odds Ratios, which are the odds of an “event” occurring in one group compared to another. In this case, “the event” is increased TSH (which, incidentally, is not a thyroid hormone, but a pituitary hormone).
For infants in which TSH was measured within 24 hours of birth, there were increased odds of having TSH greater than a level considered as the standard “cut-off” for primary congenital
hypothyroidism screening, which is the purpose of the neonatal TSH test. There were not increased odds of having TSH greater than this level when collection was after 24 hours.
This study uses data collected within the first 24 hours after birth, although there are at least two citations in the scientific literature which speak to the documented “natural TSH surge” that occurs in this period, and highlight an apparently critical flaw in the study:
- Tarone et al. (2010) states: “…analyses of TSH in the first day after birth, even if tightly controlled statistically for hours since birth, would be of questionable validity for making inferences about adverse effects of perchlorate or any other potential goitrogen on thyroid function. Results of analyses of TSH values during the first 24 hours after birth cannot be interpreted as evidence of thyroid disease, and thus there is no biologic rationale or scientific justification for evaluating these very early TSH measurements in studies of potential harm from perchlorate exposure.”
- The American Academy of Pediatrics states, “…specimens collected in the first 24 to 48 hours of life may lead to false-positive TSH elevations…It is highly desirable that the blood be collected when the infant is between 2 and 4 days of age, but there are situations in which this is virtually impossible.”
The paper uses a level of 6 ppb to categorize mothers as “exposed” or “unexposed;” this concentration is well below the scientifically recognized “no effect” level of 245 ppb in drinking water, as identified by the National Academies of Science 2005 report, “Health Implications of Perchlorate Ingestion.”
The public should be assured that 50 years of authoritative scientific research, including recent reports by the National Academy of Sciences and the EPA Office of the Inspector General, all lead to the same conclusion: low levels of perchlorate do not pose a threat to public health. For additional information please refer to research by Pearce (2010), Amitai (2009) and Kelsh 2004.
For more on this topic, visit www.perchlorateinformationbureau.org.