New Study Suggests Perchlorate Effects on Thyroid Function of U.S. Women

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New Study Suggests Perchlorate Effects on Thyroid Function of U.S. Women

 

 

 

Researchers at the Centers for Disease Control and Prevention (CDC)

have released findings showing that American women, particularly those

with low iodine intake, may have reduced thyroid function due to

perchlorate exposure. Similar thyroid function changes were not found

for men.

 

 

 

 

Newswise — Early last year, a National Academy of Sciences (NAS) panel

concluded its review of research on the health effects of perchlorate,

an inorganic anion and component of rocket fuel known to inhibit the

thyroid's ability to absorb iodine from the bloodstream, by

recommending a new reference dose. The NAS also called for further

research to identify safe exposure levels for sensitive

subpopulations. Now, researchers at the Centers for Disease Control

and Prevention (CDC) have released findings showing that American

women, particularly those with low iodine intake, may have reduced

thyroid function due to perchlorate exposure. Similar thyroid function

changes were not found for men.

 

Perchlorate's main use is as an oxidizer in solid rocket fuels. Other

uses include explosives, road flares, and pyrotechnics, and the

chemical can also form naturally in the atmosphere. A combination of

these sources has led to the widespread presence of perchlorate in

groundwater, drinking water, and foods including milk, vegetables,

fruit, grain, and forage crops. Large doses of perchlorate have been

shown to inhibit iodide uptake and reduce thyroid hormone production.

Prolonged reduction in thyroid hormone can cause metabolic problems in

adults and abnormal neurodevelopment during gestation and infancy.

 

The researchers examined 2,299 men and women, aged 12 and older, who

participated in the CDC's National Health and Nutrition Examination

Survey (NHANES) during 2001–2002. Examining the relationship between

perchlorate concentrations in urine and concentrations of the thyroid

hormones thyroxine (T4) and thyroid-stimulating hormone (TSH) in

blood, researchers observed that perchlorate was a significant

predictor of thyroid hormone levels in women, but not in men.

 

After seeing evidence of this gender difference, the authors focused

their analysis on women. They categorized a total of 1,111 women into

higher-iodine and lower-iodine groups using a cutpoint of 100

micrograms iodine per liter of urine (µg/L), then compared the women's

urinary perchlorate concentrations to their blood levels of T4 and

TSH. They found a slight relationship between perchlorate

concentrations and TSH for the higher-iodine group, but a much

stronger one for perchlorate and both T4 and TSH in women in the

lower-iodine group.

 

For the lower-iodine group, increased perchlorate was associated with

less production of T4 and more production of TSH (which usually is

produced to stimulate T4), suggesting competitive inhibition of

thyroid iodine uptake by perchlorate. Women at the 50th percentile for

urinary perchlorate had levels of 2.9 µg/L perchlorate, which

predicted a decrease in T4 of 1.06 µg/dL; at the 95th percentile of

perchlorate (13 µg/L), the predicted decrease in T4 was 1.64 µg/dL.

Although the size of perchlorate's predicted effect on T4 and TSH was

small to moderate depending on the amount of perchlorate exposure,

given that the normal range of T4 for women is between 5 and 12 µg/dL,

these predicted reductions were significant and indicate that even

small increases in perchlorate exposure may inhibit the thyroid's

ability to absorb iodine from the bloodstream.

 

In the United States, 36% of women have urinary iodine levels less

than 100 µg/L, the same as the women in the lower-iodine group in the

study. This study is the first to examine women with lower iodine

levels for a potential effect of perchlorate on thyroid function. CDC

researchers say that since this is the first time studying these

women, another large study is needed to confirm these findings; they

are planning that study.

 

The lead author of the study was Benjamin C. Blount of the National

Center for Environmental Health, CDC. Other authors included James L.

Pirkle, John D. Osterloh, Liza Valentín-Blasini, and Kathleen L. Caldwell.

 

The article is available free of charge at

http://www.ehponline.org/members/2006/9466/9466.pdf. EHP is published

by the National Institute of Environmental Health Sciences (NIEHS),

part of the U.S. Department of Health and Human Services. EHP is an

Open Access journal.

 

© 2006 Newswise. .