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Hashimoto’s thyroiditis is an autoimmune disease that affects the thyroid gland. Hashimoto’s often damages the thyroid gland to the extent that it causes hypothyroidism – an underactive thyroid. Diagnosed cases of Hashimoto’s thyroiditis have increased significantly since the 1950s, making it one of the most common autoimmune diseases and hormonal disorders among Americans.
What’s behind this rapid increase in the number of people with Hashimoto’s – and resulting hypothyroidism? Genetics can’t explain it solely because it takes at least two generations to acquire and transfer gene mutations. Many experts are now looking at environmental exposures and nutritional imbalances as potential triggers for the rising rates of Hashimoto’s and other autoimmune diseases. Let’s look at 12 factors that may be causing the rise in Hashimoto’s thyroiditis.
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Evolutionarily speaking, people have spent much of history coexisting with bacteria, viruses, and toxins, giving the immune system an important job: to defend the body against these “invaders.” In the past century, however, our environment and lifestyles have turned increasingly “hygienic,” leaving the immune system fewer invaders to fight against. Experts believe that increased rates of allergies and autoimmune diseases – including Hashimoto’s thyroiditis –are the result.
This is called the “hygiene hypothesis.” It theorizes that early childhood exposure to germs, infectious agents, gut flora, and parasites helps the immune system develop and prevents the development of allergies and autoimmune diseases later in life.
The hygiene hypothesis is clearly at work with autoimmune type 1 diabetes: the disease is the lowest in areas with the poorest hygiene conditions. The hypothesis is backed up by various epidemiological data, particularly migration studies, showing that subjects moving from a low-incidence place to a high-incidence area acquire the risk of the high-incidence area.
Iodine is a building block of thyroid hormone, and iodine deficiency can cause a goiter, contributing to hypothyroidism. The thyroid needs around 150 to 450 micrograms of iodine daily to function properly. Once iodine intake exceeds this range, hypothyroidism and autoimmune thyroid disease can occur or worsen.
Research has shown that elevated iodine levels can contribute to Hashimoto’s thyroiditis by slowing down the thyroid and causing the immune system to attack it. This triggers and worsens Hashimoto’s and accelerates thyroid cell destruction.
In iodine-sufficient individuals, iodine excess causes iodine toxicity, elevating thyroid stimulating hormone (TSH) levels and inhibiting thyroid hormone production, triggering or worsening hypothyroidism.
Selenium deficiency is among the most common nutrient deficiencies in people with Hashimoto’s thyroiditis. Experts even believe that selenium deficiency is a trigger factor for the onset of Hashimoto’s in some people. Multiple studies have shown that selenium supplementation can significantly reduce thyroid antibodies, an indicator of thyroid autoimmunity.
While Americans obtain most of their selenium from everyday staples like breads, Brazil nuts, seafood, and organ meats are the richest food sources. Other sources include muscle meats, cereals and other grains, dairy products, tofu, whole wheat pasta, mushrooms, and shrimp.
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Selenium is a trace mineral that is essential to many of the body’s regulatory and metabolic functions.
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Vitamin D and thyroid hormone bind to similar hormone receptors, and a gene in the vitamin D receptor appears to be the connection between vitamin D and thyroid function.
Vitamin D deficiency is considered a trigger for Hashimoto’s thyroiditis. In fact, research has shown that treating Hashimoto’s patients with Vitamin D may slow down the development of hypothyroidism and decrease cardiovascular risks. In Hashimoto’s disease, vitamin D deficiency appears to correlate with higher levels of Thyroid Peroxidase (TPO) antibodies and the size of the thyroid gland itself.
Studies have also shown that vitamin D deficiency is common in patients with Hashimoto’s thyroiditis. Research also shows that vitamin D treatment may slow the development of hypothyroidism and significantly reduce antibodies.
Several drugs and medications may cause – or increase the risk of developing – Hashimoto’s thyroiditis and hypothyroidism. These include:
Amiodarone: Amiodarone is a medication used to treat heart rhythm disorders, but it contains high levels of iodine that may damage the thyroid gland and trigger Hashimoto’s thyroiditis.
Interferon-alpha: Interferon-alpha is a medication used to treat certain types of cancer, viral infections, and autoimmune diseases. However, this drug can cause autoimmune thyroiditis, including Hashimoto’s thyroiditis, in some cases.
Lithium: Lithium is a medication used to treat bipolar disorder and depression. However, long-term use of lithium can cause thyroid dysfunction, including hypothyroidism and Hashimoto’s thyroiditis.
Sulfonamides: Sulfonamides are antibiotics used to treat bacterial infections. These drugs can trigger autoimmune diseases, including Hashimoto’s thyroiditis, in susceptible individuals.
Interleukin-2: Interleukin-2 is a medication commonly used to treat cancers or leukemia and improve cancer survival and clinical response to treatment. However, about 2% of patients taking this medication may develop thyroiditis, which can lead to hypothyroidism.
Tyrosine kinase inhibitors: Tyrosine kinase inhibitors (TKIs) are a type of cancer therapy that comes in pill form and targets specific types of leukemia cells. Popular TKI drugs include sunitinib (Sutent) and sorafenib (Nexavar). Studies show that up to 40% of people who take a TKI will develop hypothyroidism, which can happen anywhere from a few weeks to several months after starting the medication.
Checkpoint inhibitors: Checkpoint inhibitors are a form of immunotherapy. These medications help the body recognize and attack cancer cells. Some popular drugs in this category include nivolumab (Opdivo), pembrolizumab (Keytruda), and ipilimumab (Yervoy). These drugs can cause changes in various hormones throughout the body, including thyroid hormones. Studies have shown that anywhere from 4% to almost 14% of people taking these medications develop hypothyroidism.
Thalidomide: Thalidomide is a medication used to treat various conditions, including multiple myeloma and leprosy. Although rare, some research has reported people developing hypothyroidism due to thalidomide therapy.
Infections, particularly bacterial and viral infections, have been implicated in triggering autoimmune thyroiditis, including Hashimoto’s thyroiditis. The immune system creates antibodies that attack thyroid cells as if they were foreign bodies, leading to cell damage and death. While infections are not the only cause of Hashimoto’s thyroiditis, they are considered a major factor in autoimmune disease in general.
Bacterial infections that have been linked to Hashimoto’s include:
- Helicobacter pylori (which causes ulcers)
- Borrelia burgdorferi (which causes Lyme disease)
- Yersinia enterocolitica
An important note about Yersinia enterocolitica: Eating raw pork infected with this bacteria can cause an infection called yersiniosis. Yersinia bacteria, in particular, is associated with Hashimoto’s thyroiditis, with antibodies to Yersinia found more frequently in people with Hashimoto’s.
Viruses that have been linked to Hashimoto’s include:
- Epstein-Barr virus
- Herpes Simplex
- HTLV-1
- Hepatitis C
- Human parvovirus B19
- Coxsackie virus
Several studies have found a higher prevalence and risk of developing Hashimoto’s thyroiditis and anti-thyroid antibodies among residents living in areas surrounding petrochemical complexes.
One study conducted a cross-sectional analysis with a comparison group to investigate a possible excess of Hashimoto’s thyroiditis and antibodies in the surroundings of a petrochemical complex.
While the exact mechanism behind this relationship is not yet fully understood, it is thought that exposure to environmental pollutants such as polychlorinated biphenyls (PCBs) and dioxins may play a role in the development of autoimmune thyroid disease.
People have an increased risk of developing hypothyroidism if exposed to pesticides, fungicides, and herbicides. The growth in synthetic pesticide production and use started in the 1940s. DDT was the most popular, and its discoverer even earned a Nobel prize. In 1962 the potentially toxic effects were outlined by Rachel Carson in her book Silent Spring. According to the Stockholm Convention on Persistent Organic Pollutants, 9 out of 12 of the most dangerous and persistent pollutants are currently pesticides.
Chemicals associated with an increased risk of developing Hashimoto’s thyroiditis and hypothyroidism include:
- organochlorine pesticides (DDT, heptachlor, lindane, and toxaphene)
- herbicides (paraquat)
- fungicides (maneb, mancozeb, benomyl)
- organophosphates (diazinon and malathion),
- N-methylcarbamates (carbofuran)
Perchlorate is a chemical compound used for various industrial and commercial purposes. It is used as an oxidizer in flares, pyrotechnics, explosives, and numerous other applications, including rocket fuel, fireworks, and road flares. Perchlorate is also used in airbags for vehicles, matches, and signal flares. It is commonly used in solid rocket propellants, munitions, and electroplating operations. Perchlorate is increasingly found in our groundwater, surface water, and soil.
Perchlorate exposure has been linked to adverse effects on thyroid function, including Hashimoto’s thyroiditis. Perchlorate disrupts normal thyroid function by reducing iodine uptake from the bloodstream, which is necessary to produce thyroid hormones.
Production of polychlorinated biphenyls (PCBs) began in the late 1920s, and they were widely used until the end of the 1970s when many countries banned them due to environmental concerns. These human-made chemicals are very stable, however, so about 10% of PCBs produced remain in our environment today. Before the ban, industries using PCBs frequently dumped them in lakes and rivers. That’s why PCBs are found in food (mostly fish, meat, milk, and eggs) and human biological samples (blood, milk, and fat)
Exposure to PCBs can cause various health effects in humans. These include reproductive deficiencies, such as reduced growth rates, impaired development, neurological effects, and cancer. PCBs affect the thyroid gland by disrupting thyroid hormone balance. They can trick the body into mistaking them for hormones, interrupting hormonal balance. They may also disrupt thyroid hormone signaling, leading to thyroid disease.
Bisphenol-A (BPA) is a chemical compound primarily used to manufacture polycarbonate plastics. This type of plastic is used to make some types of beverage containers, compact disks, shatterproof windows, eyewear, water bottles, and epoxy resins that coat some metal food cans, bottle tops, and water supply pipes. BPA can enter our bodies by eating or drinking foods heated in plastics, food stored in metal cans or plastics, and other sources.
Exposure to BPA is a concern because of the possible health effects on the brain and prostate gland of fetuses, infants, and children. BPA exposure has been linked to several health problems, including obesity, diabetes, hypertension, cardiovascular disease, infertility, and cancer. Additional research suggests a possible link between BPA and increased blood pressure, type 2 diabetes, and other health problems.
BPA can bind to thyroid hormone receptors — which are virtually present on all cells in the human body — resulting in blocked thyroid hormone function. TPO antibody levels also rise with increased BPA exposure. One explanation for that might be an individual’s exposure to BPA before birth. Research has shown that maternal BPA exposure causes increased inflammation in their offspring.
Radiation exposure (whether accidental or for medical purposes) started around the mid-1930s.
Medical radiation is one of the most common approaches used to treat cancer. Radiation to the head and neck region can cause hypothyroidism. Specifically, an estimated 3 in 10 people receiving head or neck radiotherapy will develop hypothyroidism — usually within the first five years.
Nuclear medicine imaging techniques that use radioactive iodine also can trigger thyroid issues. Depending on the amount, as the radioactive iodine decays, it can damage thyroid gland function.
Radioactive iodine, capable of damaging the thyroid gland, is also present in the air – and then settling in the food and water supply -- after exposure downwind to the contaminants from nuclear disasters like Chornobyl and Fukushima.
Radiation can damage blood vessels, cells, and thyroid tissue, causing an autoimmune reaction and, in some cases, inducing hypothyroidism. The total dose, as well as the size of the irradiated area, are the most critical factors associated with the risk of developing a thyroid condition after radiation exposure.
Iodine and the thyroid
Iodine is a crucial component of the molecular structure of thyroid hormones. Learn more about the connection between Hashimoto's and iodine.
While changes to your DNA from generations of toxic exposures are irreversible, various factors affect how your genes express themselves. This is known as epigenetics. Epigenetic changes are reversible and can be influenced by environmental factors such as diet, stress, and continued exposure to toxins.
Environmental toxins and nutritional imbalances are clearly playing an epigenetic role in the development of Hashimoto’s. The thyroid is very susceptible to damage from environmental toxins and dietary imbalances.
While it’s almost impossible to eliminate all exposure to toxins, limiting your exposure can reduce your risk. And research shows that lifestyle changes such as a healthy diet, physical activity, and stress management can also positively affect epigenetics and gene expression.
Consider working with Paloma Health’s team of thyroid experts for a whole-body approach to treating Hashimoto’s and hypothyroidism. Our team will clearly outline your treatment options and explain the potential benefits of any recommended medication, supplements, and diet and lifestyle changes. Together, you and your Paloma team will develop a thyroid care plan that’s right for you and helps optimize your health. It’s a smart and holistic approach to hypothyroidism diagnosis and treatment.
Paloma Health’s Director of Research, Vedrana Högqvist Tabor, Ph.D., contributed to this article.
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