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How Environmental Toxins Harmthe Thyroid

The prevalence of thyroid disease has

skyrocketed within the past few decades.According to the American ThyroidAssociation, an estimated 20 million Americanshave some form of thyroid disease. (1) Thisalarming trend begs the question—what isresponsible for the epidemic of thyroiddysfunction? A growing body of researchindicates that exposure to environmental toxinsis a key piece of the thyroid disease puzzle.Read on to learn about the types of toxins thatare harmful to the thyroid and how you canhelp your patients minimize their toxicexposures and protect their thyroid health.

Contents [hide]

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What Types of Toxins Affectthe Thyroid?Industrial Chemicals ImpairThyroid FunctionPesticides and HerbicidesInduce HypothyroidismToxins in Common HouseholdProducts Harm the ThyroidHeavy Metals: Not a Friend tothe ThyroidTips for Reducing Exposure toThyroid-Disrupting Toxins

What Types of Toxins Affect theThyroid?

The thyroid is a small but vitally important endocrinegland located in the base of the neck. It releases asteady stream of hormones that are intrinsically involvedin the regulation of metabolism, as well as endocrine,cardiovascular, neurological, and immune function.Despite the powerful role the thyroid plays in the body,it is quite susceptible to damage from exogenousinfluences such as environmental toxins. This is due inpart to the fact that several categories of environmentaltoxins bear a structural similarity to thyroid hormones. Inaddition, the thyroid gland has a naturally high affinityfor halogens and metals. While this affinity is intended todraw iodine (a halogen) and selenium (a metalloid) intothe thyroid for the production and metabolism of thyroidhormones, it can also lead to the accumulation ofharmful halogens and metals within the gland. The typesof toxins that affect the thyroid are thus primarilysubstances that mimic thyroid hormone structure,contain halogens, or are heavy metals. These toxins can

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be divided into four main groups based on their source:industrial chemicals, pesticides and herbicides, toxins inconsumer goods, and heavy metals.

Industrial Chemicals Impair ThyroidFunction

Environmental pollution is increasing at a worrying rateworldwide. Three of the most common industrialpollutants are perchlorate, polychlorinated biphenyls(PCBs), and dioxin. These three pollutants have beenfound to significantly disrupt thyroid function.

Perchlorate is a highly reactive compound that isprimarily man-made; small amounts of perchlorate occurnaturally in the soil of arid environments, but thecontribution of these to environmental contamination isminimal. Perchlorate is widely used in militaryapplications, including rocket fuel and explosives, as wellas in the production of leather, rubber, paint, andbatteries. Perchlorate accumulates in surface water,groundwater, soil, and food grown in contaminated soil.Drinking water, grains, produce, and dairy products fromanimals raised on contaminated soil may containelevated levels of perchlorate. (2)

The thyroid gland is the primary target of perchloratetoxicity in humans. (3) Urinary perchlorate levels, whichare representative of the body’s burden of perchlorate,are associated with decreased thyroxine (T4) and

Are environmental toxins contributing to the

epidemic of thyroid disease? #thyroid

#thyroidhealth

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increased thyroid-stimulating hormone (TSH). (4)Research also indicates that perchlorate can disruptthyroid function at both high and low doses, overturningthe commonly held belief in toxicology that “the dosemakes the poison.” (5) Perchlorate contains chlorine,which is a halogen with the same ionic charge as iodine.Perchlorate thus disrupts thyroid function by competingwith iodide, an essential component of T4, for uptakeby the thyroid gland. This results in reduced thyroidhormone production. Research indicates that low iodineincreases one’s vulnerability to the effects ofperchlorate. Conversely, a greater intake of iodine mayhelp protect the thyroid from the disruptive effects ofperchlorate. (6, 7)

Polychlorinated biphenyls, or PCBs, are another group ofindustrial toxins that have harmful effects on the thyroid.These man-made chemicals are resistant to temperatureand pressure and have thus been used in electricalequipment, as lubricants, and in the production ofplastics, adhesives, and paints. Despite being banned inthe United States in 1979, PCBs continue to resistdegradation and persist in the environment. Researchindicates that PCBs disrupt thyroid function through avariety of mechanisms. They suppress the production ofthe thyroid hormone receptor, reducing the number ofreceptors with which thyroid hormone can bind in thebody. (8) PCBs bind to thyroid transport proteins,decreasing circulating T4, and impair liver enzymesresponsible for converting T4 to T3. (9, 10, 11) PCBs havealso been found to raise thyroid antibody levels andpromote enlargement of the thyroid gland. (12, 13) Thepresence of chlorine (a halogen) in PCBs, as well as thestructural similarity between PCBs and thyroid hormone,

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helps to explain the broad spectrum of effects that PCBshave on the thyroid.

Like perchlorate and PCBs, dioxin is a byproduct ofmanufacturing processes, including pesticide and plasticproduction. Dioxin exposure at levels consideredstandard in the United States has been associated withdecreased T4 and reduced thyroid function, withfemales more significantly affected than males. (14)Dioxin mimics thyroid hormone structure and appears todecrease T4 by binding to cell receptors that enhanceglucuronidation, a biochemical process that facilitatesthe excretion of hormones from the body.

Pesticides and Herbicides InduceHypothyroidism

Pesticides and herbicides are another group of highlyprevalent environmental toxins that adversely affectthyroid function. Exposure to organochlorine pesticides,the herbicide paraquat, and the fungicides benomyl andmaneb/mancozeb has been associated with an increasedincidence of hypothyroidism in women. (15) The use of awide variety of other pesticides, includingorganophosphates and carbamates, has been associatedwith hypothyroidism in men. (16) Pesticides andherbicides disrupt thyroid function by interfering withthyroid hormone gene expression, inhibiting thethyroid’s uptake of iodine, binding to thyroid hormonetransport proteins, reducing cellular uptake of thyroidhormone, and increasing thyroid hormone clearancefrom the body. (17, 18)

Toxins in Common HouseholdProducts Harm the Thyroid

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Ideally, a person’s home should be their haven, a saferetreat from the outside world. However, modern-dayhomes can unfortunately contain a plethora of toxins,some of which have a significant impact on the thyroid.Flame retardants, known in the scientific literature aspolybrominated diphenyl ethers (PBDEs), are one classof toxins found in consumer goods that may harm thethyroid. They are found in items such as computer andTV screens, furniture, carpet padding, and synthetictextiles. PBDEs contain bromine, a halogen, and thushave a predilection for the thyroid. Flame retardantsdisrupt thyroid function by mimicking the structure ofthyroid hormone; they displace T4 from thyroidhormone-binding proteins, preventing T4 from beingtransported in the blood. They also compete with T4 forthyroid hormone receptor binding sites and disruptestrogen activity. This unique interaction may makepostmenopausal women especially susceptible to thethyroid-disrupting effects of PBDEs. (19, 20)

Plastics are ubiquitous in our homes, appearing in items

such as food storage containers, water bottles, personalcare products, and children’s toys. Many plasticizers,such as BPA and phthalates, mimic the structures ofnatural hormones and thus have a disruptive effect onthe endocrine system, including thyroid function.Bisphenol A (BPA), found in food-can linings and plasticbottles, has been found to alter thyroid structure and actas an antagonist to T3 at thyroid hormone receptors. (21,22) Phthalates, used in vinyl flooring, adhesives, plastics,and as emollients in personal care products, also disruptthyroid function by inhibiting the binding of thyroidhormone to its receptors. (23)

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Finally, two more common household toxins that disruptthyroid function are the antibacterial chemical triclosan,found in products such as liquid hand soap, and PFOA,used in non-stick cookware and stain-resistant fabrics.Animal studies suggest that triclosan and PFOAdecrease T4, ultimately lowering thyroid function. (24,25, 26)

Heavy Metals: Not a Friend to theThyroid

Heavy metals are pervasive in our environment, andresearch continues to emerge demonstrating theirharmful effects on human health. The heavy metals withthe most significant impact on thyroid function arecadmium, lead, mercury, and aluminum.

Cadmium is a heavy metal that is released into theenvironment through mining and smelting and is alsoubiquitous in phosphate fertilizers, sewage sludge,batteries, pigments, and plastics. Chronic cadmiumexposure has been found to precipitate multinodulargoiter, reduce the secretion of thyroglobulin, andinitiate thyroid cell hyperplasia, which may lead tothyroid cancer. (27, 28)

The contamination of our environment with lead, anothertoxic heavy metal, has increased substantially due toindustrialization, mining, and the previous use of lead ingasoline. Lead is also found in paint in older homes,inexpensive metal jewelry, and children’s toys.Occupational exposure to lead has been associatedwith depressed thyroid function and elevated TSH. (29)Lead may alter thyroid function by causing deiodinationof T4. While it is not clear whether current lead exposurelevels experienced by the U.S. population adversely

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affect thyroid function, it is important that we remainaware of the potential thyroid health risks posed by thisheavy metal. (30)

Finally, mercury and aluminum exposure are inverselyassociated with thyroid hormone levels. Commonsources of mercury exposure include dental amalgams,seafood, and pollution from coal-burning power plants.Sources of aluminum include antacids, body careproducts such as deodorant, food additives, andaluminum-based cookware. Mercury accumulates in thethyroid and reduces iodide uptake, thus inhibitingthyroid hormone production. (31) Animal studiesindicate that aluminum oxidatively damages thethyroid, which subsequently affects iodide uptake andthyroid hormone production. (32) Aluminum alsotriggers an immune response that can lead to theproduction of antibodies, some of which may target thethyroid. (33)

Tips for Reducing Exposure toThyroid-Disrupting Toxins

While environmental toxins are ubiquitous, there aremany ways in which we can help our patients reducetheir exposure to these chemicals and ultimately protectand improve their thyroid health.

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Make sure your patients have optimal levels ofiodine and selenium. Optimal iodine and seleniumintake has been found to attenuate the toxic effectsthat heavy metals and perchlorate can have on thethyroid.Encourage your patients to purchase a high-qualitywater filter for their drinking and bathing water;municipal tap water can be a significant source oftoxins. However, a water pitcher filter is not enoughif one hopes to remove as many toxins as possible.Reverse-osmosis filters, on the other hand, havebeen found to effectively remove perchlorate,pesticides, PCBs, plastics, and a wide variety ofheavy metals.Recommend that your patients eat organic food asmuch as possible. This will help them avoidexcessive pesticide and herbicide exposure. Theyshould also be encouraged to cease usingpesticides in their homes and yards.Encourage your patients to stop using syntheticantibacterial products and to limit their use ofplastics at home. If they still choose to use someplastic products, recommend that they look for“BPA-free” options. However, keep in mind thatBPA-free products may still contain other bisphenolderivatives with potential thyroid-disrupting effects,so it really may be best to entirely avoid drinkingfrom or storing food in plastic containers.Recommend that your patients stop using non-stick cookware. PFOA from non-stick cookware canleach into food and is subsequently ingested.Suggest that they use stainless steel or enameledcast iron cookware instead.

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If you are interested in learning more about the healthimpacts of environmental toxins and what factorsinfluence one’s susceptibility to toxins, check out myprevious article “Environmental Toxins: The Elephant inthe Room?” For more information on how you can helpyour patients reduce their toxic exposures, check out myarticle “Environmental Toxins: Steps for DecreasingExposure and Increasing Detoxification.”

CHRIS KRESSERFounder of the Kresser Institute. Health detectivespecializing in investigative medicine, blogger,podcaster, teacher and a Paleo diet and lifestyleenthusiast.

View other articles by Chris Kresser

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12 Comments

Bonnie McLean

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September 7, 2017 at 5:36 am

If you didn’t listen to Dr. Patrick Gentempo’sdocumentary series GMO’s Revealed, it’s veryinformative, especially Dr. Zack Bush.

Brooke Lounsbury

September 7, 2017 at 5:49 am

I recommend staying out of hot tubs and swimmingpools. Bromine, found in many pool and spa productsto disinfect affect thyroid function. I recommend forhot tubs tea tree oil and geranium oil. Works like acharm.

Donna K J

September 7, 2017 at 6:53 am

I did not see mention of fluoride. My dentist insists oncleaning my teeth and then applying fluoride. Whatdo you think of this practice?

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Matt

September 7, 2017 at 8:26 am

Yes, fluorine (fluoride), another VERY commonhalogen needs to be avoided. It is used to treatwater and very difficult to filter out. It is taken upby the thyroid when it is deprived of iodine.

Flouride-free toothpaste, and do not let thedentist use flouride, bring your own fluoride freetoothpaste to your dental cleanings and have themuse that for the buffering.

Do your best to avoid the common halogens:– Chlorine– Bromine– Fluorine

Virginia

September 7, 2017 at 8:20 pm

There is a definite relationship between Fl andthyroid health since Fl is a halogen and competeswith iodine just like Br and Cl. You can simply letyour dentist know that you don’t want Fl and keepin mind its usually in the tooth polish too.

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Tina

September 7, 2017 at 9:03 am

I am wondering what you use for testing heavymetals. I have heard many concerns with challengetesting and redistribution of metals. So I would like tohear your thoughts.

Susan

September 7, 2017 at 10:46 am

The only halogen mentioned in this article waschlorine with regard to perchlorate. Just as muchemphasis should be placed on chlorine in tap water,the water we bathe in, hot tubs and swimming pools.The other halogens of concern, which were notmentioned are fluorine and bromine. Fluoride isadded to most municipal water, and of course is aningredient in dental products. Bromides are added tomost baked goods.Chlorine, fluorine and bromine all displace iodine andtherefore can affect thyroid function.Another environmental toxin not mentioned whichharms the thyroid is mold.

Michelle

September 7, 2017 at 11:12 am

Great article and great suggestions about what tostop doing and using — but it would be really helpful

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to have some specific suggestions on what to do oruse instead. Recommendations for a good(affordable) filter? Recommendations for a type ofcookware to use? There are so many options it can beparalyzing. I hate to ask for more “free” info – you areso generous with your knowledge, but I also knowyou “live” this life, so you probably can provide somegreat tips. Thanks for all you do!

Charlotte

September 7, 2017 at 6:33 pm

I am curious about the effects of radon. I haven’t beenable to find much in Pub Med. However if theradiation from radon is enough to affect the risk oflung cancer, it seems intuitive it would affect thesensitive tissues of the thyroid. Any thoughts?

Amanda

February 7, 2018 at 3:11 pm

My thoughts exactly. I was looking for the sameinformation. Radon levels are supposedly high inmy area and there is very little informationavailable about it.

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Ed

September 8, 2017 at 3:26 am

Do you test for toxic exposures in every hypothyroidpatient you see? If so, what percentage test positiveand have the condition reversed by your detoxprotocol? Seems like an expensive standard practicewithout clear evidence of efficacy.

Richard Thomas

November 17, 2017 at 5:42 am

Re; Problems with the parathyroids.I presume the above would apply to these as well.