Combined effects of perchlorate, thiocyanate, and iodine on thyroid function in the National Health and Nutrition Examination Survey 2007-08.
Level 4 - case-series / case-control
Cross-sectional observational analysis of survey data (NHANES 2007-2008).
PubMed 23473920 · doi:10.1016/j.envres.2013.01.005
What was done
Cross-sectional analysis of 2007-2008 NHANES data evaluating urinary perchlorate, thiocyanate, and iodine concentrations in relation to mean serum thyroxine concentrations. Participants were stratified into individual exposure groups and a combined exposure group (high perchlorate, high thiocyanate, low iodine) compared against a low-exposure reference group (low perchlorate, low thiocyanate, adequate iodine).
What was found
Subjects with high perchlorate (n=1939) had 5.0% lower thyroxine concentrations (mean difference=0.40 ug/dl, 95% CI 0.14 to 0.65) than subjects with low perchlorate (n=2084). Individual effects of iodine and thiocyanate were smaller. Subjects with combined high perchlorate, high thiocyanate, and low iodine (n=62) had 12.9% lower thyroxine concentrations (mean difference=1.07 ug/dl, 95% CI 0.55 to 1.59) than subjects with low perchlorate, low thiocyanate, and adequate iodine (n=376). Potential confounders had little impact on results.
Why it matters
Assessing single environmental toxicant exposures in isolation may underestimate thyroid disruption, as simultaneous co-exposure with low iodine intake showed a substantially larger reduction in circulating thyroxine.
Limits
Cross-sectional design cannot establish causality. The combined high-exposure group was relatively small (n=62). Exposures were based on spot urine samples without longitudinal tracking, and clinical outcomes or TSH levels were not reported in the abstract.
Cited by
- supports Consuming 150 micrograms of iodine daily is protective to the thyroid gland against thyroid-targeting chemicals.