Household Toxins

Polybrominated diphenyl ethers (PBDEs), more commonly referred to as flame retardants, populate many areas of the modern-day home such as furniture, carpet padding, clothing made of synthetic materials, and the screens of electronic devices. PBDEs imitate thyroid hormone structure allowing PBDEs to bind to a particular class of proteins called transporters that T4 usually binds to, thereby blocking T4 from being transported in the blood. This activity disturbs estrogen function making postmenopausal women especially vulnerable to PBDEs.

Bisphenol A (BPA) and phthalates, ingredients used to make plastic for water bottles, children’s toys, and food storage containers, imitate the structures of other hormones found naturally in the body and disrupt the entire endocrine system along with the thyroid.BPA changes the structure of the thyroid gland and inhibits T3 from binding to another class of proteins called receptors which T3 uses to produce changes in the body while phthalates also inhibit T3 from binding to its receptors. Thyroid function is also diminished by triclosan, an antibacterial agent found in some liquid hand soaps, and perfluorooctanoic acid, or PFOA, an agent used in stain-resistant fabrics, food wrappers, and non-stick cookware.

Industrial Chemicals

The most prevalent industrial chemicals are dioxin, perchlorate, perfluorinated chemicals, or PFCs, and polychlorinated biphenyls, or PCBs. All four of these pollutants negatively affect thyroid function. Dioxin, a byproduct of pesticide production, plastic making, and other manufacturing processes, reduces thyroid function by mimicking thyroid hormone structure and decreasing T4 levels. These effects arise even at standard dioxin levels; that is, low levels of dioxin that exist in the environment, yet are considered unavoidable.

Small concentrations of perchlorate arise naturally in the soil of arid regions, but the high levels polluting the environment come from applications involving the development of airbags, batteries, fireworks, leather, paint, jet/rocket fuel, and rubber. From there, perchlorate seeps into surface water, groundwater, drinking water, soil, and ultimately food grown in the ground. Once in the body, perchlorate lowers T4 levels, competes with iodide for uptake into the thyroid gland, and reduces thyroid hormone production. Even low levels of perchlorate toxicity can produce these effects yet consuming more iodine may protect the thyroid from perchlorate.

The use of PFCs has been on the decline, however, from mattresses and detergents to food packaging and fire extinguishers, many imported goods still contain PFCs. PFCs disrupt overall thyroid function by either increasing thyroid hormone production to dangerously high levels or decreasing thyroid hormone production to dangerously low levels. These effects appear to depend on gender, as women with PFC toxicity tend to develop hyperthyroidism while men with PFC toxicity tend to develop hypothyroidism.

For their ability to resist pressure and temperature, PCBs are widely used as lubricants, in electrical equipment, and for adhesive, paint, or plastic production.

PCBs disturb thyroid function by:

1. reducing the number of receptors available for T3 to bind to
2. decreasing the amount of T4 circulating in the bloodstream (T4 is needed for conversion into T3), and
3. preventing liver enzymes from converting T4 into T3.

Other studies have found that PCBs enlarge the thyroid and can increase TSH levels to the point of making the body resistant to thyroid hormones. Again, PCBs achieve these effects by copying the structure of thyroid hormones.

Agricultural Agents

Perhaps the first culprits to come to mind in discussions of environmental toxins; pesticides, herbicides, and fungicides weaken thyroid function to the point of causing hypothyroidism or “low thyroid.” Hypothyroidism induced by agricultural agents is typically seen in women overexposed to pesticides containing organochlorine, paraquat herbicide, benomyl fungicide, or maneb/mancozeb fungicide. Men with hypothyroidism induced by agricultural agents are usually overexposed to organophosphates, carbamates, or other pesticides. Agricultural agents wreck thyroid function by altering thyroid hormone gene expression, preventing the uptake of iodine into the thyroid, blocking thyroid hormone from binding to its transport proteins, lowering the absorption of thyroid hormone into thyroid cells, and promoting thyroid hormone removal from the body.

Thyroid Diseases Induced by Environmental Toxins

Among all heavy metal toxins, chronic toxicity with aluminum, lead, and mercury can further damage the thyroid by recruiting antibodies to attack the thyroid. This process contributes to the development of autoimmune thyroid diseases (AITD), such as Graves’ disease and Hashimoto’s thyroiditis. Research has yet to determine the physiological mechanisms by which AITD manifests; however, two causes have been identified—environmental toxicity and genetic predisposition.

Because the production of antibodies against the thyroid does not always escalate into AITD, AITD arises in approximately only 5% of individuals and those individuals are more often women. Studies explain the reason for this is that females’ immune systems are more reactive than males’ even in other species. This evolutionary feature helps females fight off disease more effectively, most likely to ensure reproduction for healthy population growth. However, in humans, this places the woman’s thyroid at even greater risk of AITD. Men are not entirely excluded from AITH with their less reactive immune systems though, as scientists have found that contracting any of the following viruses enhances the incidence of Thyroid Diseases:

• Acquired Immunodeficiency Syndrome (AIDS)
• Enterovirus
• Epstein-Barr Virus
• Hepatitis C (HCV)
• Herpes Simplex Virus
• Human Immunodeficiency Virus (HIV)
• Human Parvovirus B19 (EVB19)
• Human T-cell Lymphotropic Virus-1
• Mumps
• Rubella