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The Effects of Perchlorate on Thyroid Health

Published November 4 2013

Perchlorate is an environmental contaminant that blocks iodine/iodide uptake into the thyroid gland (1) [1].  I first learned about perchlorate a number of years ago when reading Dr. David Brownstein’s well known book “Iodine, Why You Need It, Why You Can’t Live Without It”.  In addition to the detrimental effects this toxin can have on thyroid health, in his book Dr. Brownstein also discussed how perchlorate can also disrupt the menstrual cycle and cause weakening of the immune system.

But where does perchlorate come from?  It is the main ingredient in rocket fuel, and is also used in ammunition, fireworks, highway safety flares, air bags, and fertilizers (2) [2].  It occurs as a contaminant in ground and surface water in many areas of the United States (3) [3].  For example, it is estimated that more than 16 million people in California drink contaminated water from the Colorado river (2) [2].  One study I came across showed that perchlorate is present in many rain and snow samples, which strongly suggests that some perchlorate is formed in the atmosphere (4) [4].

The Environmental Working Group conducts a great deal of research on environmental factors which affect our health.  And if you visit their website (www.ewg.org) and conduct a search for perchlorate, you’ll see just how widespread this toxin is.  One thing you’ll notice is that at least 162 sites in 36 states have known manufacturers or users of perchlorate.  On their website you can also view a map which lists the counties in the Unites States where there have been confirmed perchlorate contamination of drinking water, groundwater, or surface waters.  And this information is updated.

How Does Perchlorate Impact Thyroid Health?

As I mentioned earlier, perchlorate can block iodine uptake into the thyroid gland.   The way that perchlorate blocks this mineral is by affecting the iodine transport mechanism (the sodium/iodine symporter), which prevents the further synthesis of thyroid hormone (5) [5].  So this in turn can lead to a hypothyroid condition.  In fact, perchlorate was used as an antithyroid drug for hyperthyroidism in the 1950s and 1960s, but was discontinued because of the occasional occurrence of aplastic anemia (6) [6].  As for whether perchlorate can trigger an autoimmune thyroid condition, there hasn’t been much research in this area, although a large study of pregnant women in Chile with high perchlorate exposure showed no increase in autoimmune thyroid disease or antibodies in pregnancy or the postpartum period. (7) [7].

Earlier in this article I discussed some of the common sources of perchlorate, and another study I came across detected perchlorate in all seven brands of dairy milk randomly purchased from grocery stores in Lubbock, Texas (8) [8].  The same study discussed how perchlorate in 47 dairy milk samples from 11 states and in 36 human milk samples from 18 states were measured, and perchlorate was detectable in 81 of 82 samples.  This of course isn’t good news for those people who drink milk, but it also is bad news for lactating women.  The reason is because as I mentioned earlier, perchlorate inhibits iodine uptake, and the same study I just mentioned also measured the levels of iodide, and found that the presence of perchlorate in the milk lowers the iodine content and may impair thyroid development in infants.  Another study evaluated the associations between maternal drinking water and perchlorate exposure during pregnancy and newborn thyroid hormone levels (9) [9].  The findings of the study suggested that perchlorate is associated with increased neonatal TSH levels.

This can pose a problem with those women who have Hashimoto’s Thyroiditis, as many healthcare professionals recommend for people with this condition to completely avoid iodine.  And even though I’m pro-iodine, I’m admittedly cautious about recommending iodine supplementation to people with Hashimoto’s.  However, while there is the risk that taking iodine can exacerbate the autoimmune response, low iodine intake during pregnancy, or low iodine present in the breast milk can affect the health of the baby, and so perhaps a small amount of iodine is warranted in these cases.

Does Perchlorate Exposure Alone Cause Problems With Thyroid Function?

There was a review of the epidemiological literature which looked to evaluate the risk of adverse effects on thyroid function associated with environmental perchlorate exposure (10) [10].  They concluded that “there is no credible or consistent evidence from any of the numerous studies using a variety of designs that environmental exposure to perchlorate has any adverse effect on thyroid function, whether measured as changes in thyroid hormone levels or, among newborns, as the diagnosis of primary congenital hypothyroidism” (10) [10]. They were more concerned with other goitrogens, such as nitrates and thiocyanate.

Another study confirmed this, as they discussed how nitrates and thiocyanate account for a much larger proportion of iodine uptake inhibition than perchlorate (11) [11].  Yet another study discussed how the combined exposure to perchlorate, thiocyanate, and low iodine markedly reduces thyroxine production (12) [12].

So what does all of this mean?  Well, I truly believe that perchlorate exposure is something to be concerned about.  However, this doesn’t mean that everyone who is exposed to perchlorate will develop hypothyroidism, or that most lactating women need to be concerned about the perchlorate content in breast milk.  Someone who has sufficient levels of iodine and isn’t being exposed to other goitrogens such as thiocyanates very well might not need to be concerned about perchlorates.

The problem is that most people aren’t aware if they are being exposed to either perchlorates or thiocyanates.  And many people who are iodine deficient aren’t aware of this either.  And even if someone is iodine deficient, as I mentioned earlier, many people with an autoimmune thyroid condition are hesitant to supplement with iodine to correct this deficiency.  There is testing to determine the levels of perchlorate, but it’s not something recommended by most healthcare professionals.

There really is no easy solution, but for someone with Hashimoto’s Thyroiditis, while perchlorate might be an issue, in most cases it’s probably safe to conclude that the elevated thyroid antibodies are responsible for the hypothyroid condition.  And as I mentioned earlier, perchlorates don’t seem to trigger an autoimmune response, although this can’t be completely ruled out.  On the other hand, for someone who has hypothyroidism without an autoimmune component, one might want to consider testing for perchlorate.  Before doing this I would test to make sure the person doesn’t have an iodine deficiency.

In summary, perchlorate can block the uptake of iodine into the thyroid gland, and potentially can cause hypothyroidism.  According to the Environmental Working Group, perchlorate is a big issue, and there are numerous manufacturers of perchlorate throughout the United States.  However, there is some controversy as to whether exposure to perchlorate alone can inhibit thyroid function.  Perhaps one needs to be exposed to very high levels for this to happen, or as some studies suggest, other factors might need to be present, such other goitrogens and/or an iodine deficiency.  Of course since perchlorate can affect the health of other areas of the body, one still will want to do everything they can to minimize their exposure to this toxin.