Thyroid Disruption and Exposure

How Perchlorate Disrupts the Thyroid

The thyroid gland concentrates iodine from the bloodstream using a protein called the sodium-iodide symporter (NIS). Perchlorate binds to NIS with higher affinity than iodide itself, effectively blocking iodine uptake. With less iodine entering the thyroid, production of T3 and T4 — the hormones that regulate metabolism, energy, and development — falls. The pituitary gland compensates by releasing more thyroid-stimulating hormone (TSH), which is why elevated TSH on a blood test can signal perchlorate burden alongside other causes.

The key moderating factor is iodine status. When dietary iodine is plentiful, the competition from perchlorate is partially overcome by sheer quantity of iodide. The 2006 NHANES study of 2,299 Americans found that in women with low urinary iodine, perchlorate significantly predicted lower T4 and higher TSH — but effects were much weaker in women with adequate iodine intake [1]. This is why maintaining sufficient iodine is the most practical protective step.

Perchlorate does not act alone. Nitrate (from well water, vegetables, and processed meats) and thiocyanate (from cruciferous vegetables and cigarette smoke) block the same NIS transporter. Their combined burden is more predictive of thyroid disruption than any single chemical measured in isolation [5].

Where Exposure Comes From

Water: Industrial contamination is widespread. Rocket testing and production facilities have contaminated groundwater in Nevada, California, Texas, and other states. The Colorado River — drinking water for Los Angeles and San Diego — was contaminated from a Henderson, Nevada facility. Roughly 70% of US military installation groundwater samples tested between 1997 and 2009 contained measurable perchlorate. The EPA has proposed a drinking water limit of 20 µg/L (the rule has been in progress since 2011 and is expected to be finalized in 2027).

Food: An FDA survey found detectable perchlorate in at least one sample of 74% of common foods tested. The highest concentrations appear in dairy products, leafy greens, and some root vegetables, because plants absorb perchlorate through their roots from contaminated soil and irrigation water [6]. Chilean nitrate fertilizers used in agriculture are a natural source of perchlorate that has spread into agricultural soils globally.

Infant formula: All types of commercially produced formula contain measurable perchlorate — detected in 100% of samples in multiple studies. Cow's milk-based formula tends to carry higher concentrations than soy-based varieties. When formula is prepared with tap water that is also contaminated, exposures can exceed the EPA reference dose [4].

Breast milk: Perchlorate was detected in 100% of breast milk samples in a Boston-area study, with concentrations ranging widely (1.3 to 411 µg/L). About half of the nursing women in that study appeared to be providing breast milk with potentially insufficient iodine — a compounding problem, since the infant faces both lower iodine supply and active competition from perchlorate [3].

Who Is Most Vulnerable

Pregnant women and fetuses are the highest-priority concern. The fetal brain depends entirely on maternal thyroid hormone through the first half of pregnancy, before the fetal thyroid is functional. Even modest reductions in maternal T4 during this window have been associated with lower IQ, delayed motor development, and attention deficits in children. The Steinmaus 2016 study of nearly 1,900 pregnant women in Southern California found perchlorate exposure associated with meaningful decreases in both total T4 (β = −0.70) and free T4 (β = −0.053), and increased TSH [2].

Formula-fed infants face exposure from both the formula itself and any perchlorate in the water used to prepare it. Infants have high metabolic demands for thyroid hormone relative to their body weight and less iodine reserve than adults.

People with low iodine intake — including those avoiding iodized salt, dairy, and seafood — have less buffer against NIS competition. Iodine deficiency and perchlorate exposure together create a worse outcome than either alone [5].

Practical Steps to Reduce Exposure

Water filtration: Reverse osmosis (RO) systems effectively remove perchlorate from drinking water and are the most practical point-of-use option. Standard activated carbon filters — pitcher filters, most faucet filters — do not remove perchlorate. This distinction matters especially when preparing infant formula.

Iodine sufficiency: The most evidence-backed protective factor is maintaining adequate iodine intake. Sources include iodized salt, seaweed (kelp, nori), dairy, eggs, and seafood. The RDA for iodine is 150 µg/day for adults, rising to 220 µg during pregnancy and 290 µg while breastfeeding. Many prenatal vitamins do not include iodine, or include too little — check the label.

Produce: Washing vegetables reduces surface-level contamination but does not remove perchlorate absorbed into plant tissue. Buying organic reduces some pesticide and fertilizer-source contamination, but naturally occurring perchlorate in soil means organic is not entirely protective.

See our water filtration page for a broader look at what's in tap water. For more on the thyroid, see our thyroid health pages.