Most thyroid disorders are autoimmune in nature. Even if thyroid hormone imbalances initially are triggered by iodine deficiency or excess, the immune system responds by producing thyroid antibodies. Thyroid antibodies, depending on their nature, can destroy thyroid tissue or stimulate it to produce excess thyroid hormone.
Thryoglobulin antibodies destroy thyroid tissue in Hashimoto’s thyroiditis; blocking TSH receptor antibodies lead to atrophic thyroiditis by preventing pituitary stimulation, and stimulating TSH receptor antibodies (TSI, thyroid stimulating immunoglobulins) cause Graves’ hyperthyroidism by ordering thyroid cells to produce excess hormone. Thyroid peroxidase antibodies result from thyroid inflammation and lead to a persistence of this inflammation.
Besides iodine, a number of other factors such as pesticides, toxins, goitrogenic foods, viruses, and low selenium levels, have been discovered to impact thyroid function. To date, ionizing radiation is the only known trigger for thyroid cancer. Researchers reporting in Environmental Health Perspectives (Brown 2003) emphasize that that the thyroid gland along with breast tissue and bone marrow, is especially vulnerable to ionizing radiation, including radioiodine.
Iodine and Thyroid Hormone
Iodine is necessary for the production of thyroid hormone. Thyroid hormone is formed when iodine combines with the amino acid tyrosine. However, the thyroid gland can’t distinguish iodine from radioiodine, and it absorbs radioiodine easily. The World Health Organization estimated in 2003 that 740 million people worldwide suffer from iodine deficiency. Iodine deficiency is particularly prevalent in undeveloped countries without access to ocean fish, kelp and sea salt or where foods that block iodine (goitrogens), such as cassava and millet, are excessively consumed. In contrast, 57% of people in the developing world regularly use iodized salt and commonly receive excess amounts of an unnatural form of iodine that has aluminum added to prevent caking.
Iodine deficiency can lead to hypothyroidism and iodine excess can lead to hyperthyroidism. The effects of iodine excess can be transient such as those seen in mini-epidemics of Graves’ disease caused by meat contaminated with thyroid hormone. Chronic iodine excess or deficiency can, as mentioned, trigger the immune system to produce antibodies that lead to autoimmune thyroid disease.
Endocrine Disruptors and Thyroid Health
A number of chemicals including fluoride can displace iodine molecules and disrupt normal endocrine function. Even very subtle reductions in circulating levels of thyroxine (T4), which may not result in altered laboratory values, can affect physiological processes.
This is especially important during fetal development when low thyroxine levels are characterized by small stature, low birth weight, and vision and motor disturbances. Some neurodevelopmental problems such as extreme mental retardation and deaf-mutism can result when the fetus is not provided with adequate thyroid hormone. Children of hypothyroid mothers, even with treatment, have a higher than normal incidence of difficulties with spatial, perception, memory, language and other skills.
Endocrine disruptors include polychlorinated biphenyls (PCBs) and related compounds such as polybrominated diphenyl ethers (PBDEs), the fungicidal ethylenebisdithiocarbamate (EBDCs), dioxin and perchlorate. Further complicating matters, each of these compounds may have subtypes or congeners that have weaker, stronger or no disruptive endocrine actions. Recent evidence shows a clear association between Agent Orange and the development of Graves’ disease. In addition the EBDC fungicides sprayed on many plants including root and leafy vegetables and cereal grains have been known since the 1960s to cause goiter and inhibit iodine uptake. Perchlorate is common in drinking water in the southwestern United States as a contaminant from missile and rocket fuel.
Immune Stimulants and Thyroid Health
Exposure to allergens, infectious agents and toxins stimulates the immune system. Over time with chronic exposure to allergens or toxins, including aspartame and cigarette smoke, or inadequate treatment, the immune system becomes ineffective and fails to launch a normal immune response. Unable to gauge clear threats, the immune system targets the body’s own tissues and cells, triggering autoimmune thyroid disorders. For instance, ingestion of gluten by individuals with gluten sensitivity can stimulate the development of thyroid antibodies and autoimmune thyroid disease. In these cases, a gluten free diet can reduce levels of autoantibodies that contribute to both thyroid disease and gluten sensitivity.
Iatrogenic refers to effects caused by medical treatments and diagnostic tests or physicians. Various medications and treatments can adversely affect thyroid function. Iodine contrast dyes cause excess accumulations of iodine in fatty tissues that can cause transient episodes of hyperthyroidism lasting several months. Drugs such as interferon and interleukin used for hepatitis, malignancies and certain autoimmune diseases, can trigger the development of various autoimmune disorders, most notably autoimmune thyroid disorders and diabetes.