Thyroid Health and Nutrition

Caring for every organ is essential to our overall health.

The thyroid is a small gland located in the front of the neck, but it plays a massive role in the human body. It synthesizes the hormones triiodothyronine (T3) and thyroxine (T4), which are key to growth and development, influence heart and cardiovascular function, and regulate metabolism.

Thyroid disorders are common. Reduced thyroid function, known as hypothyroidism, affects 2.2–6.3% of the population, while overactive thyroid function—hyperthyroidism—affects 0.8–3.7%. The prevalence of Hashimoto's thyroiditis in Europe ranges between 5% and 10% of the general population. Thyroid nodules larger than 5 mm are found in 24.4% of Bulgarians.

Nutrition is one of the most important environmental factors affecting thyroid function. Through food, the body obtains the micronutrients necessary for hormone synthesis and the maintenance of normal immune function.

Iodine

Iodine is an essential micronutrient for the synthesis of thyroid hormones, as it is a structural component of them. When iodine is deficient, hormone synthesis decreases, leading to increased secretion of thyroid-stimulating hormone (TSH) by the pituitary gland and subsequent enlargement of the thyroid gland.

Iodine deficiency during pregnancy can lead to impaired mental and physical development of the fetus, as well as an increased risk of miscarriage.

Excessive iodine intake can also have an adverse effect on thyroid function. High doses often cause temporary suppression of thyroid hormone synthesis, and chronic excessive intake can lead to iodine-induced hyperthyroidism or hypothyroidism, especially in people with pre-existing thyroid conditions. For this reason, taking dietary supplements containing seaweed or high levels of iodine without medical consultation is not recommended.

Iodizing table salt is considered the most effective method for ensuring adequate iodine intake among the population.

Recent studies and reports from the World Health Organization (WHO) indicate that mild to moderate iodine deficiency is once again being observed in Europe and Bulgaria. The main reasons cited include the growing popularity of alternative types of salt (pink Himalayan, sea, rock salt) that are not iodized, as well as reduced consumption of dairy products and processed foods containing iodized salt3.

Selenium

Selenium is another extremely important micronutrient for normal thyroid function. It is involved in the activity of enzymes required for the synthesis and activation of thyroid hormones.

Selenium deficiency is linked to various thyroid disorders, including hypothyroidism, subclinical hypothyroidism, and autoimmune diseases such as Hashimoto's thyroiditis and Graves' disease.

Studies show that selenium supplementation may lead to a slight decrease in TSH levels and anti-TPO antibodies in patients with normal thyroid function or subclinical hypothyroidism who are not receiving hormone replacement therapy.

Dietary sources of selenium:

• Nuts and seeds: Brazil nuts, sunflower seeds, chia, sesame;
• Fish and seafood: tuna, salmon, shrimp, oysters;
• Meat and poultry: turkey, chicken breast, beef liver, pork;
• Dairy products: hard cheeses, cottage cheese, yogurt;
• Eggs;
• Grains and legumes: oatmeal, brown rice, lentils, whole-grain bread.

Iron

Iron is the third key micronutrient required for the normal production of thyroid hormones. When deficient, cells become less sensitive to the action of these hormones.

Iron deficiency and anemia are often linked to hypothyroidism. Conversely, hypothyroidism can impair iron absorption in the gastrointestinal tract, which explains why these two conditions frequently occur together.

Dietary sources of iron:

Animal sources (better absorption):

• liver;
• red meats (beef, lamb);
• poultry, especially turkey;
• fish and seafood.

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Plant-based sources:

• legumes;
• nuts and seeds;
• leafy greens (spinach, sorrel, nettle, broccoli);
• oatmeal, quinoa, buckwheat.

Vitamin D

Vitamin D is a powerful immune system modulator. It can reduce levels of thyroid antibodies—anti-TPO and TgAb. Maintaining optimal vitamin D levels is recommended for patients with Hashimoto's thyroiditis.

Zinc

Zinc (Zn) is involved in gene regulation and numerous enzymes essential for the synthesis and metabolism of thyroid hormones. Furthermore, it has a strong antioxidant effect and can reduce autoimmune inflammation and damage to the gland.

Zinc-rich foods:

• oysters and fish;
• legumes;
• nuts;
• red meat;
• whole grains.

Magnesium

Magnesium (Mg) supports the action of thyroid hormones and has an anti-inflammatory effect.

Sources of magnesium:

• leafy green vegetables;
• legumes;
• nuts and seeds;
• milk;
• whole grains.

Other important nutrients

Vitamin A and vitamin B12 are also important for normal thyroid function and should be present in sufficient amounts in your diet.

Omega-3 fatty acids have a strong anti-inflammatory effect and support the cellular response to thyroid hormones.

Proteins, especially those rich in L-tyrosine, are essential for building thyroid hormones, as L-tyrosine serves as their protein base.

Foods rich in L-tyrosine:

• turkey and chicken;
• fish;
• eggs;
• cottage cheese;
• pumpkin seeds;
• bananas.

Goitrogens – should they be avoided?

There are natural compounds in some foods called goitrogens that can reduce iodine absorption and affect thyroid function, but this is primarily observed when consuming very large quantities of raw products.

Such foods include:

• broccoli;
• cauliflower;
• cabbage;
• Brussels sprouts;
• kale;
• raw soy;
• millet.

Heat treatment (boiling, baking, steaming) significantly reduces or completely neutralizes the effect of goitrogens.

Conclusion

Nutrition can significantly support thyroid function and play an important role in the prevention and treatment of thyroid disorders. A balanced intake of essential micronutrients, vitamins, and high-quality proteins is a vital part of taking care of our health.

Author: Dr. Stella Yordanova, Endocrinologist

References

1. Borisova AM et al. Epidemiology of endocrine diseases in Bulgaria 2006–2012.

2. Vargas-Uricoechea H. et al. A Scoping Review on the Prevalence of Hashimoto’s Thyroiditis and the Possible Associated Factors.

3. Stfeva et al. Endocrine Abstracts. The neonatal TSH screening as an indicator of the iodine status in newborns in Bulgaria: actual data 2021–2024.

4. Shulhai AM, Rotondo R, Petraroli M, Patianna V, Predieri B, Iughetti L, Esposito S, Street ME. The Role of Nutrition on Thyroid Function. Nutrients. 2024;16(15):2496.