What else in our diet blocks iodine from the thyroid?

  •   Nitrates, thiocyanate and other compounds found naturally in everyday foods like broccoli, cauliflower, meats and leafy vegetables: 99%
  •   Perchlorate: less than 1%. Perchlorate is naturally found in organic fertilizer and in a variety of defense and industrial applications.

Source: Epidemiology of Environmental Perchlorate Exposure and Thyroid Function: A Comprehensive Review (Tarone, et al, June 2010)

In the human body at high doses, perchlorate can compete with iodine, which the thyroid gland uses to make hormones. This effect is called iodide uptake inhibition, or IUI, and this effect is not adverse. Notably, in its 2005 report, the National Research Council of the National Academies of Science (NAS) in the United States confirmed that IUI is not an adverse health effect, and that adverse effects of perchlorate exposure are only theoretical and have not been demonstrated in humans.

There is little or no likelihood that dietary perchlorate intake could result in adverse effects because sufficient iodine intake reduces any effects perchlorate may have on the human thyroid.

In its 2008 Total Diet Study, the FDA found that dietary iodine consistently exceeded current Estimated Average Requirements. That study also found that most perchlorate-containing foods contain relatively higher levels of iodine. The FDA does not recommend any changes to infants’ and children’s diets or eating habits based on current perchlorate data.
Explore FDA’s Questions and Answers »

The American Thyroid Association noted in a 2004 press release that it is highly unlikely the levels of perchlorate detected in foods have any measurable health effect.
Read the American Thyroid Association press release »