Hashimoto’s thyroiditis is the most common form of autoimmune thyroiditis which occurs as a result of a complicated interaction between susceptibility genes and environmental factors. A wide variety of environmental agents adversely affect the thyroid gland and hormone production.
The following environmental factors can trigger autoimmune thyroiditis and contribute to the disease progression in genetically predisposed individuals:
- infections (bacteria, viruses and parasites)
Iodine deficiency contributes to thyroid diseases, the enlargement of the thyroid gland, hypothyroidism and mental abnormalities in children. Low iodine levels had been endemic in many areas of the world. With the introduction of iodized salt in the 1920s, iodine deficiency and incidence of goiter dramatically reduced in most of the industrialized countries. However, at the same time autoimmune thyroiditis became the most common cause of hypothyroidism.
Currently an excess of dietary iodine is the best established environmental factor that compromises thyroid function, causes goiter and autoimmune thyroiditis in susceptible individuals. Long-term iodine exposure leads to increased iodination of thyroglobulin, which then is recognized as an antigen by the immune system and initiates the autoimmune response. Highly iodinated Tg is more immunogenic than poorly iodinated Tg.
Both high and low iodine levels can cause thyroid inflammation and Hashimoto’s disease. There are no reliable way to find out if you have iodine excess or deficiency other than make iodine test. You can read more on how high iodine intake affects thyroid health in the FREE Nutritional Guide for Hashimoto’s and hypothyroidism.
In humans the function of the thyroid gland can be compromised by dietary factors other than iodine. An increased prevalence of autoimmune thyroid dysfunction has been reported in patients with celiac disease, where a permanent intolerance of dietary gluten causes inflammation and mucosal damage to the intestinal lining.
Celiac disease and Dermatitic herpetiformitis are relatively common in people with Hashimoto’s thyroiditis with a prevalence of approximately 20% to 25%, however many patients who are either asymptomatic or have subtle symptoms remain undiagnosed.
A higher incidence of gluten intolerance was found associated with many if not all autoimmune diseases. Prevalence of celiac disease was noted to be in a range of 1% to 19% in patients with type 1 diabetes mellitus, 2% to 5% in autoimmune thyroid disorders and 3% to 7% in primary biliary cirrhosis.
There is also a high prevalence of immune disorders including Hashimoto’s thyroiditis among patients with celiac disease. (1) According to Dr. Datis Kharrazian and new studies, all Hashimoto’s patients have some degree of gluten intolerance or a full-blown celiac disease. Gluten can cause disease in many ways by damaging intestinal walls, contributing to leaky gut syndrome, malabsorption, nutritional deficiencies, increasing thyroid autoimmunity and many others.
The coexistence of celiac and autoimmune thyroid disease is partly due to a common genetic predisposition. Both celiac disease and Hashimoto’s thyroiditis are reported to be associated with the genes CTLA-4, HLA-DQ2 and HLA-DQ8 that are also present in many other autoimmune conditions.
Many Hashimoto’s and celiac disease patients who go gluten-free do not see any difference in their symptoms. According to Dr. Peter Osborne there are more than 400 other gluten-like proteins that are found in other grains and particularly in corn that can cause damage in people with celiac disease and gluten sensitivity. He has better results when his patients follow his True Gluten-Free Diet recommendations that he describes in his book Truth About Gluten as compared to those who goes on the traditional gluten-free diet.
Gluten has been shown to have a cross-reactivity with 24 other common foods such as dairy, amaranth, yeast, chocolate, potatoes, sesame seeds and coffee. It means that those with gluten sensitivity can also react to these foods as they react to gluten. People with Hashimoto’s disease can have cross-reactivity with other foods that can cause an increased autoimmune responce and contribute to the development of this health condition.
Changes in the intestinal flora and its activities are a one of contributing factors to many chronic, degenerative and autoimmune diseases. Modern Western diet, antibiotics, psychological and physical stress can cause intestinal dysbiosis which has a detrimental impact on the microflora of the gastrointestinal tract. At dysbiosis, levels of good intestinal bacteria are dramatically diminished and bad bacteria such as candida overgrowth, heliobacter and parasites are increased. Dysbiosis as well as food allergies supress the immune system and are quite likely to result in leaky gut which is one of the underlying causes for many unexplained symptoms and autoimmune diseases including Hashimoto’s.
Bacterial, viral and parasitic infections are known to initiate and worsen autoimmune diseases. They may act alone or together with environmental chemicals. Hashimoto’s thyroiditis has been linked to infections with hepatitis C, Epstein-Barr virus (EBV), HTLV-1 virus, Helicobacter pylori and Yersinia enterocolitica. There is strong evidence that acute parvovirus B19 infections are involved in some cases of Hashimoto’s thyroiditis. (2)
Both hypothyroidism and thyroid autoimmunity are more common in individuals with hepatitis C compared to the general population. At the same time, higher levels of Tg antibodies and significant increase in the risk of autoimmune thyroiditis were established in patients with hepatitis C. (3)
Infections cause autoimmune thyroid diseases mainly by the mechanism of molecular mimicry, also called cross-reactivity, that is based on structural similarities between microbial antigens and thyroid autoantigens leading to over reactivity of the immune system. (4)
For example, microbic antigens such as Borrelia and Yersinia proteins share amino acid sequence structure with self antigenes and act as environmental triggers of autoimmune thyroid diseases (Grave’s and Hashimoto’s). The levels of antibodies to these proteins can be significantly high confirming bacterial exposure that leads to Hashimoto’s in genetically predisposed individuals. (5)
Helicobacter pylori causes a chronic infection that usually lasts a life-time and is associated with a wide spectrum of gastric, cardiovascular and respiratory tract diseases, growth retardation, headache and migraine, and with organ specific autoimmune diseases. The World Health Organisation (WHO) estimates show that approximately 50% of the world’s population are infected with Helicobacter pylori, however the majority of infected subjects develop no clinical symptoms.
Infectious agents such as Helicobacter pylori may cause chronic inflammation and autoimmune reactivity in susceptible individuals. An interaction between HLA-DRB1*0301 gene and Helicobacter pylori infection as well as higher occurrence of Helicobacter pylori itself, TPO antibodies and anti-Helicobacter pylori antibodies have been found in the patients with Hashimoto’s disease. (6) You can get tested for H. pylori.
In the conventional medicine antibiotics are prescribed to treat Helicobacter pylori. However, there is a safe and clinically proven natural method to completely eradicate all strains of Helicobacter pylori using Matula Herbal Formula without negative side effects.
Amiodarone is an iodine containing drug, which is prescribed to patients to treat arrhythmia (irregular heart beat). A greater frequency of increased thyroid peroxidase antibodies (TPO Ab) was found in female patients using amiodarone especially when the treatment lasted longer than 24 months. (7)
Chronic administration of the drug may lead to disturbances in thyroid hormone metabolism and thyroid dysfunction. Amiodarone inhibits peripheral conversion of T4 into T3 that results in increase of serum freeT4, reverse T3 and TSH concentrations and a decreased serum level of free T3. Amiodarone may induce thyrotoxicosis or hypothyroidism in the individuals with normal or increased iodine levels and/or pre-existing thyroid disease.
Interferons are currently the major treatment approach for several malignant and non-malignant diseases such as chronic hepatitis C and B, multiple sclerosis, hematological malignancies, malignant melanoma and renal cell carcinoma. Both autoimmune and non-autoimmune thyroid disorders develop in some of the interferon treated patients with the incidence ranging from 1% to 35%.
Interferon induced thyroiditis is a common complication of interferon alpha (IFNα) treatment of chronic hepatitis C with up to 10% of patients developing clinical thyroiditis and up to 30% developing subclinical autoimmune thyroiditis.(8)
Lithium is a common treatment for bipolar disorder, which is also called manic depression. The drug inhibits release of the thyroid hormones contributing to the development of hypothyroidism, goiter, and changes in the texture of the gland detectable by ultrasound. Lithium may also cause chronic autoimmune thyroiditis with hypothyroidism in 20 to 40% of patients. Up to 50% of lithium-treated patients may develop a lithium-induced goiter after 2 years of therapy. (9) Use of lithium in combination with pharmacological doses of potassium iodide may also result in hypothyroidism.
Over 90 synthetic chemicals were noted to show disruptions of the hormone balance or thyroid dysfunctions (10). Many of these compounds are widely distributed through the environment. However, only few environmental pollutants show evidence that they contribute to autoimmune thyroid disease.
Such environmental pollutants as smoke, synthetic chemicals, solvents and heavy metals have been implicated to affect thyroid function and cause inflammation and autoimmune response. Man made pollutants include pesticides, polyaromatic hydrocarbons (PAH), polybrominated biphenols (PBBs), and polychlorinated biphenols (PCBs).
Perchlorate is an inorganic anion that occurs naturally in soil and is also made synthetically. This chemical compound can inhibit iodide uptake by the thyroid gland from the bloodstream leading to the suppression of T3 and T4 hormones. Perchlorate contamination has been documented in grains, fruits, vegetables, dietary supplements, milk, drinking water and forage crops for livestock. (11)
The main threats to human health from heavy metals are associated with exposure to lead, cadmium, mercury and arsenic. Some of them could cause high levels of thyroid antibodies and trigger Hashimoto’s disease.
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3. Interferon induced thyroiditis. Best Pract Res Clin Endocrinol Metab. 2009 Dec;23(6):703-12.
4. Association of parvovirus B19 infection and Hashimoto’s thyroiditis in children. Viral Immunol. 2008 Sep;21(3):379-83.
5. Human thyroid autoantigens and proteins of Yersinia and Borrelia share amino acid sequence homology that includes binding motifs to HLA-DR molecules and T-cell receptor. Thyroid. 2006 Mar;16(3):225-36.
6. Anti-Helicobacter Pylori, anti-thyroid peroxidase, anti-thyroglobulin and anti-gastric parietal cells antibodies in Czech population. Physiol Res. 2008;57 Suppl 1:S135-41. Epub 2008 Feb 13.
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9. Hashimoto Thyroiditis. S.L. Lee, S. Odeke, S.B. Nagelberg, eMedicine online publication, Mar., 2010
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