Hashimoto's disease

The thyroid gland is a small, butterfly-shaped gland located in the front of the neck, just under the voice box. It plays a vital role in regulating numerous body functions, including heart rate, body temperature, metabolism, and growth and development, through the production of thyroid hormones that communicate with various cells and tissues in the body.

Hashimoto’s thyroiditis is an autoimmune disorder and the most common cause of hypothyroidism (underactive thyroid) in the U.S. and in other regions of the world with sufficient iodine intake (which is necessary for the thyroid gland to function properly). In people with Hashimoto’s disease, the immune system inappropriately targets the thyroid gland, leading to tissue damage, inflammation and scarring that ultimately decreases thyroid hormone production. The disease often appears in people who are 30-50 years old and is at least 10 times more common in women than men.^[1] Hashimoto’s disease is strongly associated with other autoimmune diseases, so your physician may search for other disorders associated with autoimmunity.

Most of the symptoms experienced by people with Hashimoto’s disease are caused by hypothyroidism, or low levels of thyroid hormones. The most common symptoms are fatigue, intolerance to cold, and constipation.^[2] People with Hashimoto’s disease may also experience any of the following additional symptoms.^[1][2]

• Depression
• Muscle and joint pain
• Dry skin
• Brittle nails
• Difficulty sleeping
• Irregular menstrual cycle
• Weight gain / appetite changes
• “Brain fog”
• Memory problems
• Hair loss
• Bradycardia (abnormally slow heart rate)
• Ataxia (poor muscle control causing involuntary movements)
• Infertility
• Loss of libido

For people with signs and symptoms of Hashimoto’s disease, a doctor will first obtain a complete medical history and family medical history, since, like many autoimmune diseases, Hashimoto’s disease can have a genetic component. A physical exam will also be performed to examine the thyroid gland and check for enlarged lymph nodes in the neck, an indication of an active immune response and characteristic symptom of Hashimoto’s disease. Specific tests will also usually be done to rule out thyroid cancer.^[3]

Ultrasound may also be performed to look for abnormalities in the thyroid gland, although for the majority of patients, it may not be essential to confirm a diagnosis of Hashimoto’s disease.^[4][1] Blood testing for hypothyroidism and autoimmunity will also be performed by measuring thyroid hormones (such as TSH, T3, and T4), and checking for antibodies against thyroglobulin and thyroid peroxidase.

Ultimately the combination of high TSH, low free T4, and anti-thyroid antibodies confirms a diagnosis of Hashimoto’s disease.^[1]

The main treatment for Hashimoto’s disease is thyroid hormone replacement to bring thyroid hormones up to normal levels. The main drug used for this purpose is levothyroxine, in doses that typically range from 1.6-1.8 micrograms per kilogram of bodyweight per day.^[1]

The following supplements have been studied for Hashimoto’s disease:

• Vitamin D^[5]
• Selenium^[6]

There are currently no specific dietary recommendations for people with Hashimoto’s disease, although deficiencies in particular micronutrients such as vitamin D, magnesium,^[7] iron, vitamin B12,^[8] and selenium have been linked to an increased risk of the disease or its severity.^[9] The role of iodine deficiency in risk of Hashimoto’s disease is complex, with some investigators suggesting that deficiency is associated with increased autoimmune hypothyroidism.^[10] However, not all researchers agree, and excess iodine intake, commonly through high consumption of iodized salt, can also worsen or trigger Hashimoto’s disease.^[9]

One pilot study tested the efficacy of an Autoimmune Protocol diet (a modified paleolithic diet) in 17 women participating in a 10-week online health coaching program. Although the participants had lower levels of inflammation after the intervention (as measured by high-sensitivity C-reactive protein (hs-CRP), there were no changes in thyroid function or autoantibody levels.^[11]

An observational study found that meat consumption is associated with increased Hashimoto’s disease risk, while Mediterranean-style diets may be protective.^[12]

Thyroidectomy (removal of the thyroid gland) may be used to treat patients whose symptoms persist in spite of obtaining normal thyroid hormone levels with replacement therapy. Persistence of symptoms in spite of bringing thyroid hormone levels up to normal is thought to be caused by the autoimmune aspect of Hashimoto’s disease.^[13]

Removal of the thyroid gland can suppress the underlying autoimmune response in the body by removing the source of antigenic tissue.^[14] A 2019 randomized controlled trial tested this idea in 150 participants with persistent symptoms in spite of normal thyroid hormone levels. In comparison to participants who received the control intervention (thyroid hormone replacement therapy only), participants who had their thyroid glands removed showed significant improvements in overall health and fatigue, and in autoantibody levels, at an 18-month follow-up.^[15]

Autoimmune-induced damage to the thyroid gland is the cause of Hashimoto’s disease. Although thyroid gland injury is the cause of hypothyroidism, patients will continue to experience characteristic symptoms as a result of the underlying autoimmunity.^[15] With autoimmune diseases, the body inappropriately interprets self-tissues as harmful pathogens, generating antibodies that cause the immune system to target parts of the body, such as the thyroid gland in Hashimoto’s disease. As with most autoimmune diseases, the mechanisms responsible for the breaking of self-tolerance are not well understood and likely involve a combination of environmental factors and genetics.

The link between Hashimoto’s disease and genetics is relatively strong, with studies in monozygotic twins suggesting that an estimated 79% of Hashimoto’s disease risk may be driven by genetic factors.^[16][1]

Although well-tolerated in healthy individuals, high dietary iodine intake can cause hypothyroid symptoms in people with Hashimoto’s disease by suppressing thyroid hormone production.^[2]