Thyroid hormones regulate energy levels and every function of the human body. At the same time, the thyroid gland is highly vulnerable to autoimmune diseases that disturb thyroid function.
The incidence of autoimmune conditions Hashimoto’s and Graves’ disease has increased dramatically over the past few decades, affecting up to 5% of the general population. This number is comparable to type 2 diabetes which is considered to be a modern epidemic.
Who Is At Risk?
Autoimmune thyroid diseases tend to be more frequent in women than in men. The reason for this gender related difference is not clear and could not be explained by additional X chromosome found in females in comparison to males.
Women have two important physiological factors that contribute to autoimmunity that are absent in men:
- Estrogens affect thyroid function and could enhance HLA-DR gene expression leading to initiation of the autoimmune reaction during major hormonal changes in puberty, by rapid growth, pregnancy, times of emotional vulnerability, near menopause and with aging. Use of oral contraceptives has protective effects for development of Grave’s disease, however not for Hashimoto’s.
- Pregnancy is a risk factor for development of autoimmune thyroid diseases due to hormonal changes and shifts of the immune system. During pregnancy the immune system becomes suppressed with a shift in the Th1/Th2 balance towards increased Th2 immunity that is intended to protect the fetus but at the same time makes women more prone to develop thyroid autoimmune disease. In about 10% of pregnant women TPO antibodies are elevated and associated with an increased risk of miscarriage, gestational thyroid dysfunction and postpartum thyroiditis.
According to one UK study, women with lower than normal birth weight (5.5 LBS) had the prevalence of TPO antibodies later in life twice as high as compared to those with higher birth weight.
People who have thyroid conditions in the family, were diagnosed with another autoimmune disease or have Turner, Down and Klinefelter syndromes are at increased risk to develop Hashimoto’s disease and should be tested.
Genetic Factors Of Thyroid Autoimmunity
Thyroid autoimmune disease results from a combination of genetic and environmental factors. Hashimoto’s and Grave’s disease have different phenotype, however appear to run in the same families, share common genetic background and the same TPO thyroid antibodies.
According to recent studies, there are two groups of genes that are associated with the thyroid disease:
- Immuno-modulatory genes HLA-DR, CD40, CTLA-4 and PTPN22
- Thyroid specific genes Tg and TSH-receptor
Genetic factors are accountable for about 80% of probability to develop an autoimmune thyroid disease, whereas 20% are due to environmental factors.
Environmental Factors Of Thyroid Autoimmune Disease
The following environmental factors can contribute to development of autoimmune thyroid disease in genetically susceptible individuals:
Iodine. The thyroid gland requires the correct amount of iodine to support its normal function. Too much or not enough iodine causes thyroid health issues. High iodine in the diet is correlated with increases in autoimmune thyroid disease making this condition more common in the iodine sufficient areas.
Selenium. Trace element selenium is a part of selenoproteins that contribute to proper function of the immune system, have antioxidant and antiviral properties, improve fertility, mood and well-being.
Adequate selenium levels may protect against autoimmune thyroid disease and goiter development in adults. Selenium supports synthesis of thyroid hormones and protects the thyroid gland from possible damage due to high iodine intake with the diet. In the areas of combined iodine and selenium deficiency, selenium levels should be normalized first in order to protect the thyroid gland from the adverse effects of iodine and prevent hypothyroidism.
Polychlorinated biphenyls (PCBs) are widely used in the industrials applications, lubricants, inks, adhesives, plastics and have a tendency to accumulate in the environment and adipose tissue of animals and humans. PCBs interfere with iodide transport and induce oxidative stress lowering thyroid hormone production and induce to hypothyroidism. In people with long-term exposure, PCBs have immune-modulating properties and increase levels of thyroid antibodies contributing to thyroid autoimmunity.
Environmental pollutants. Coal pollution, pollutants from car emissions and heavy industry also increase the incidence of autoimmune thyroid disease.
Smoking is a risk factor for development of postpartum thyroiditis and Grave’s disease and reduced remission rates after treatments with radioactive iodine. Thyroid eye disease tends to be more severe in smokers. In addition, cigarette smoking has been noted to decrease the effectiveness of orbital radiotherapy and high-dose glucocorticoids treatment. If you are a smoker it is advisable to quit smoking in order to reduce your risk of developing Grave’s and thyroid eye diseases or make an existing condition worse.
Viral, bacterial, and parasitic infections can initiate and worsen thyroid autoimmune conditions acting together with environmental chemicals or alone. Inflammation caused by viral infections or by pollutants can modify cell signalling pathways and induce autoimmunity.
For instance, Hashimoto’s disease has been associated with such infections as hepatitis C, Epstein-Barr virus (EBV), HTLV-1 virus, Borelia, H pylori and Yersinia enterocolitica. There is strong evidence that acute parvovirus B19 infections are involved in some cases of inducing the Hashimoto’s disease.
Drugs. Several drugs are known to induce autoimmune thyroid disease in genetically predisposed individuals. Amiodarone is an iodine containing drug for treatment of rapid heartbeat. The drug impairs conversion of T4 into T3 thyroid hormone leading to hypothyroidism. Amiodarone also has immune-modulating properties and increases levels of TPO antibodies in about half of the patients who received treatment.
Lithium is used to treat psychiatric disorders and has goitrogenic effect which interfere with thyroid function and reduce production of thyroid hormones. Patients who use lithium have increased thyroid antibodies more frequently than patients treated with other type of drugs.
Interferons are widely used for treatment of multiple sclerosis and different types of hepatitis. Interferon alpha IFN-α is a common drug for chronic hepatitis C. The drug can increase the levels of thyroid antibodies and disturb the thyroid function leading to hypothyroidism.
Stress. Both physical and psychological stress have immune-suppressive effect and can trigger Grave’s and thyroid eye disease.
Allergies. Allergic rhinitis is another risk factor for Grave’s disease. Patients with elevated immunoglobulin E (IgE) levels have higher incidence of Grave’s disease and lower remission chances after anti-thyroid drug treatment. Another allergic condition called chronic urticaria can contribute to Hashimoto’s disease and higher incidence of TPO and Tg antibodies.
Irradiation. Both internal and external irradiation by I-131 are associated with autoimmune thyroid disease. External irradiation increases the risk of thyroid cancer, hypothyroidism, Grave’s and thyroid eye diseases. Grave’s disease occurs in up to 5% of patients with toxic and non-toxic multinodular goiter within 6 months following the radioactive iodine treatment.
Based on the studies of nuclear bombing and Chernobyl nuclear plant accident, environmental radiation and nuclear fall-out can damage the thyroid gland, increase thyroid cancer and antibody positive hypothyroidism.
Diet. Many triggers of autoimmune conditions including Hashimoto’s disease are dietary. There is a strong link between gut health and thyroid autoimmunity. Many foods can trigger autoimmune response and bring your immune system out of balance. Most common dietary triggers are gluten, soy, eggs, dairy, nightshade group of vegetables such as tomatoes, egg plants and potatoes and many others.
How do you find out what foods trigger YOUR autoimmune response? Watch the video below where Dr Tom explains how your diet can contribute to hypothyroidism and gives you 5 simple hypothyroidism diet tips that can help you to improve your thyroid function today:
To help you get started and find your way to recover from hypothyroidism Dr. Tom offers for a limited time a FREE presentation where he shares exact 3 steps how he helps his clients to recover from hypothyroidism and Hashimoto’s disease permanently. Just click here to watch as long as it is still available.
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References:
Why is the thyroid so prone to autoimmune disease? Horm Res Paediatr. 2011;75(3):157-65. Epub 2011 Feb 22.
The environment and autoimmune thyroid diseases. Eur J Endocrinol. 2004 May;150(5):605-18.
