January is National Thyroid Awareness Month. First off, what is the thyroid? The thyroid is a small butterfly-shaped gland that is located above the collarbone and in front of the windpipe.^1–3 It is responsible for producing hormones that maintain the body's energy and regulate the body's breathing, heart rate, nervous systems, body weight, muscle strength, menstrual cycles, cholesterol levels, and other organ systems.^2,4 Therefore, thyroid disorders and diseases impair the secretion of hormones and cause dysfunction to the entire body. There are many thyroid disorders and diseases including hypothyroidism, hyperthyroidism, abnormal thyroid growth, nodules/lumps within the thyroid, and thyroid cancer.³ Hashimoto's disease is one condition that can cause hypothyroidism.

What is Hashimoto's Disease?

'Hashimoto's disease,' also known as 'Hashimoto's thyroiditis’ is the most common cause of hypothyroidism in the United States.^2,4 This condition is an autoimmune disorder that causes chronic inflammation in the thyroid which leads to impaired thyroid function, the under-production of thyroid hormones, and an underactive thyroid (which is also known as hypothyroidism).² The likelihood of developing Hashimoto's disease can increase if an individual has the following risk factors: being a woman between the ages 30-50, having a family history of Hashimoto's disease, and having other autoimmune disorders such as celiac disease, lupus, rheumatoid arthritis, and type 1 diabetes.⁴ Further, exposure to certain environmental and nutritional factors contributes to the development of this disease.⁵

Nutrition Recommendations for Hashimoto's Disease

There are currently no specific nutrition recommendations for this condition, but researchers are identifying associations between various nutrients and thyroid function.

Iodine

Iodine is essential for the body as it is a necessary component for the two main thyroid hormones triiodothyronine (T3) and thyroxine (T4).^3,5,6 Although, long-term intake of excessive or increased amounts of iodine has been associated with increases in circulating antibodies.⁵ This association likely occurs due to highly-iodinated thyroglobulin (Tg) which is immunogenic, meaning that it can trigger an immune reaction against the thyroid.⁵ Such a reaction increases the risk of thyroid autoimmunity and has been evident in multiple countries that have supplied iodine-fortified products, including China and Denmark.⁵ Based on these data, autoimmune thyroiditis, including Hashimoto’s disease, is associated with excess iodine intake. Therefore, it is recommended that sources of iodine should be eaten in moderation to ensure that iodine levels remain at the recommended levels. Iodine can be found in seafood (e.g. seaweed, fish, shellfish), animal products (e.g. cow’s milk, eggs, yogurt), and some fruits (e.g. cranberries, strawberries).⁷

Iron

Adequate iron intake is necessary for the production of T3 and T4 as the enzyme thyroid peroxidase activates after binding to a prosthetic heme group that contains iron.⁶ Notably, multiple studies have found that patients with Hashimoto's disease and hypothyroidism have lower serum iron concentrations and a higher prevalence of iron deficiency compared to healthy controls.⁶ It is good to note that individuals with Hashimoto's disease also tend to have celiac disease or another autoimmune disorder that implies that iron deficiencies may stem from those co-morbidities rather than Hashimoto's disease.⁶ Similar to iodine, it is recommended that sources of iron should be eaten in moderation so iron levels remain at the recommended levels. Iron can be found in both animal and plant sources, but animal sources are more bioavailable compared to plant sources.⁸ Some foods that contain iron include lean beef, oysters, chicken, turkey, beans and lentils, tofu, cashews, dark green leafy vegetables, and fortified or enriched bread and cereals.⁸ It is also recommended to couple a source of vitamin C with these foods to enhance iron absorption.⁸

Selenium

Selenoproteins are proteins that contain selenium and are necessary for thyroid function.⁵ Glutathione peroxidases are essential selenoproteins for thyroid function as they eliminate excessive amounts of hydrogen peroxide, which is a by-product of the iodination process of highly-iodinated Tg to form thyroid hormones.⁵ Evidence from observational studies and randomized-controlled trials have demonstrated that selenium, likely when in its selenoprotein form, can decrease thyroid peroxidase-antibody concentration and hypothyroidism.⁵ Therefore, limited selenium stores can cause thyroid dysfunction, and can especially affect individuals with Hashimoto's Disease.⁵ Notably, excessive selenium intake is toxic so selenium intake should meet recommended levels.⁵ Sources of selenium include oysters, tuna, whole-wheat bread, sunflower seeds, mushrooms, rye, and animal meats (e.g. chicken, turkey, pork, beef, lamb).⁷ Brazil nuts are also an excellent source of selenium as eating one Brazil nut will meet the daily recommended intake for selenium.

Vitamin D

Vitamin D is both a fat-soluble vitamin and a hormone as it is responsible for regulating calcium/phosphate homeostasis in the kidneys and bones, it is an immunomodulator, and it modulates cell growth and differentiation.^7,9,10 There is potential relevance of vitamin D status to Hashimoto’s disease as research has shown that lower vitamin D has been identified in patients with Hashimoto's disease compared to controls.⁶ Also, inverse relationships have been found between serum vitamin D status and thyroid peroxidase/Tg antibodies.⁶ Although, there are limited trials and evidence regarding vitamin D status and thyroid function, and populations with other autoimmune diseases have reported vitamin D receptor dysfunction implying that low vitamin D status is a result of autoimmune disease processes and is not exclusive to Hashimoto's disease.⁶ Also, one study found no significant changes in the serum levels of T3 and T4 of vitamin D deficient patients with Hashimoto’s disease, even after vitamin D supplementation.⁹ Therefore, more research is required to better understand the relationship between vitamin D and thyroid function. Vitamin D3 is the most bioavailable form of vitamin D to humans and can be found in fish (e.g. wild fresh salmon, cod liver oil, sardines) and dairy products.⁷ Further, the body can synthesize vitamin D3 in the skin via adequate sun exposure.⁷

Based on these data, individuals with Hashimoto’s disease are recommended to monitor their intake of iodine, iron, selenium, and vitamin D. The Dietary Guidelines for Americans can be referenced to determine recommended amounts for each micronutrient. Further, it may be beneficial to discuss nutrition recommendations about Hashimoto's disease or other thyroid diseases and disorders with dietitians or healthcare providers who specialize in these conditions.

If you would like to learn more about Hashimoto's disease or other thyroid diseases, then you can visit the American Thyroid Association website.

References: 

1. Clinic TS. National Thyroid Awareness Month: Thyroid Disease. The Surgical Clinic. Published January 15, 2020. Accessed January 4, 2022. https://thesurgicalclinics.com/national-thyroid-awareness-month/

2. Hashimoto’s Thyroiditis. American Thyroid Association. Accessed January 3, 2022. https://www.thyroid.org/hashimotos-thyroiditis/

3. Thyroid Gland: Overview. Endocrine Web. Accessed January 4, 2022. https://www.endocrineweb.com/conditions/thyroid-nodules/thyroid-gland-controls-bodys-metabolism-how-it-works-symptoms-hyperthyroi

4. Hashimoto’s Disease | NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. Published June 2021. Accessed January 3, 2022. https://www.niddk.nih.gov/health-information/endocrine-diseases/hashimotos-disease

5. Rayman MP. Multiple nutritional factors and thyroid disease, with particular reference to autoimmune thyroid disease. Proceedings of the Nutrition Society. 2019;78(1):34-44. doi:10.1017/S0029665118001192

6. Hu S, Rayman MP. Multiple Nutritional Factors and the Risk of Hashimoto’s Thyroiditis. Thyroid. 2017;27(5):597-610.

7. Liontiris MI, Mazokopakis EE. A concise review of Hashimoto thyroiditis (HT) and the importance of iodine, selenium, vitamin D and gluten on the autoimmunity and dietary management of HT patients. Points that need more investigation. Hell J Nucl Med. 2017;20(1):51-56. doi:10.1967/s002449910507

8. Foods to Fight Iron Deficiency. Accessed April 6, 2021. https://www.eatright.org/health/wellness/preventing-illness/iron-deficiency

9. Chahardoli R, Saboor-Yaraghi AA, Amouzegar A, Khalili D, Vakili AZ, Azizi F. Can Supplementation with Vitamin D Modify Thyroid Autoantibodies (Anti-TPO Ab, Anti-Tg Ab) and Thyroid Profile (T3, T4, TSH) in Hashimoto’s Thyroiditis? A Double Blind, Randomized Clinical Trial. Horm Metab Res. 2019;51(5):296-301. doi:10.1055/a-0856-1044

10. Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. seventh.