Diet and Thyroid – How Are They Related?

A Few Words About the Thyroid Gland

The thyroid is one of the most important endocrine glands in the human body and is located in the front part of the neck.

Endocrine glands are those that produce and secrete substances – hormones – which are transported in the bloodstream and can then affect the action of various organs and tissues located far from their place of production.

The thyroid gland produces and secretes three basic hormones:

• T4 (thyroxine). It is the hormone produced in the largest quantities by the thyroid gland. However, to exert its biological actions, it must first be converted to its active form, T3 (triiodothyronine).

• T3 (triiodothyronine). It is the active form of the thyroid hormone, thyroxine (T4). About 20% of triiodothyronine is secreted directly into the bloodstream by the thyroid gland. The remaining 80% is produced by the conversion of thyroxine by organs such as the liver, kidneys, etc.

• CT (calcitonin). It affects bone metabolism by regulating blood calcium levels.

The amount of thyroid hormones produced by the thyroid is controlled by the pituitary gland, a small endocrine gland at the base of the brain. The pituitary gland produces thyroid-stimulating hormone (TSH), which is transported through the bloodstream to the thyroid to regulate the production of thyroid hormones.

In cases where the thyroid produces a smaller amount of hormones than necessary, blood TSH levels increase, while in the opposite case they decrease.

What Are the Functions of the Thyroid Gland?

The thyroid hormones, T3 and T4, produced by the thyroid gland, can affect every cell and organ in our body.

These hormones have numerous actions in our body, including:

• They regulate the basal metabolic rate. Thyroid hormones are the main regulator of our metabolism, controlling the rate at which our body expends energy – that is, calories – to maintain its vital functions, such as breathing, thermoregulation, and heart rate.

• They regulate cardiovascular function. Thyroid hormones affect heart rate, influence cardiac output (the volume of blood ejected by the heart every minute) and the relaxation of blood vessels.

  It is no coincidence that in thyroid disorders, patients often complain of cardiovascular system discomfort. In the case of hyperthyroidism where we have increased levels of thyroid hormones, palpitations are one of the most characteristic symptoms and are attributed to increased heart rate even at rest.

• They regulate the gastrointestinal system. Thyroid hormones affect intestinal motility, that is, how quickly food is transported through the gastrointestinal tract.
• They regulate body temperature. The thyroid contributes to our body’s thermoregulation, that is, maintaining our body temperature within a normal range of values.
  Cellular metabolism is the main source of heat production in our body. Given that thyroid hormones can affect our metabolism, they can consequently affect thermogenesis and body temperature regulation.
• They affect the function of the nervous system. The normal formation of the central nervous system of the fetus throughout pregnancy and the first year after birth is directly related to thyroid hormones. The fetal thyroid begins to function and produce its own hormones from the 18^th week of gestation. Before this time point, the fetus depends entirely on the mother’s hormone production. If the mother develops unregulated hypothyroidism, this can harm the fetus and especially the development of its nervous system.
• They affect psychological state. Thyroid disorders also affect the psychological state with main manifestations of anxiety and depression, with the severity of the thyroid disease proportionally affecting mood swings. In the case of hyperthyroidism, symptoms such as unusual nervousness, restlessness, anxiety, irritability may be observed, whereas in cases of hypothyroidism, fatigue and/or depression appear.

What Are the Common Thyroid Gland Disorders?

Thyroid disorders can be divided into two categories:

• Anatomical disorders, which relate to abnormalities in the size or composition of the thyroid gland. Anatomical disorders include:

  • Goiter
  • Thyroid nodules
  • Benign or malignant neoplasia

• Functional disorders, which relate to disturbances in the way the gland functions, whether it works more or less. In this category, the main disorders are:

  • Hypothyroidism. It is a condition characterized by the thyroid gland’s inability to produce enough quantities of the thyroid hormones T3 and T4.
  • Hyperthyroidism. It is the condition in which the thyroid overworks and produces excessive amounts of hormones.

What Are the Symptoms of Hypothyroidism?

Hypothyroidism is a pathological condition in which the levels of thyroid hormones (T3 and T4) are low, meaning there is a low secretion of hormones from the thyroid gland.

The most common symptoms experienced by individuals with hypothyroidism are:

• Physical fatigue

• Cold intolerance

• Constipation

• Weight gain

• Bradycardia

• Difficulty concentrating

• Depression

• Drowsiness

• Menstrual disorders

• Reduced fertility

• Dry skin, etc.

What are the symptoms of hyperthyroidism?

Hyperthyroidism is characterized by hyperactivity, meaning the thyroid gland produces thyroid hormones in large quantities.

The most common symptoms experienced by individuals with hyperthyroidism are:

• Nervousness

• Irritability

• Feeling of palpitations

• Rapid heartbeat

• Sweating

• Heat intolerance

• Weight Loss

• Frequent bowel movements

• Fatigue, etc.

Is there an ideal diet for thyroid gland disorders?

The truth is that there is no ideal diet recommended for people with thyroid disorders.

The changes that need to be made in our dietary habits depend on many factors that should be taken into account, such as age, body weight, medical history, accompanying diseases (e.g., diagnosis of diabetes mellitus), etc.

The specialized nutritionist will inform you appropriately about the dietary modifications you will need to make through taking a detailed medical and nutritional history.

What diet should I follow if I have hypothyroidism?

Hypothyroidism is the most common thyroid disorder.

Although claims about diets for hypothyroidism are abundant, there is no scientific evidence to support that consuming or avoiding certain foods will improve thyroid function in people with hypothyroidism. In other words, there is no specific diet for patients with hypothyroidism.

It is important to emphasize that diet cannot function as a therapeutic tool for people diagnosed with hypothyroidism. The only treatment for hypothyroidism is the daily intake of appropriate medication aimed at restoring thyroid hormone levels to normal levels.

Of course, it is important for people with hypothyroidism to follow a diet that will ensure adequate intake of nutrients essential for good thyroid function.

Which nutrients affect thyroid function?

Some nutrients that have been linked to thyroid function are:

Iodine

Iodine is important for the production and synthesis of thyroid hormones.

Iodine deficiency can lead to reduced production of thyroid hormones and consequently to hypothyroidism.

The daily recommended intake of iodine for adult men and women has been set at 150μg.

Iodine naturally exists in seawater and soil. Nowadays, iodine deficiency is rare as it is found in satisfactory amounts in table salt.

In the early 20^th century, iodine deficiency was more common, which led to the formulation of a global strategy for Universal Salt Iodization (USI), as an effort to protect population health.

The fortification of table salt with iodine has ensured adequate iodine intake through diet.

Imagine that 1 teaspoon of iodized salt contains 310μg of iodine, which covers our daily needs by almost 200%!

Of course, there are other good dietary sources of iodine such as:

• Seaweed

• Shellfish

• Fish

• Dairy Products

• Eggs

• Certain fruits and vegetables. The iodine content depends on the iodine content of the soil, water, and fertilizers used in cultivation.

The table below shows some foods and the amount of iodine they contain.¹

Food	Amount of Iodine (μg)
100 g cooked cod	172,0
2 tablespoons dried Nori seaweed	116.0
100 g cooked oysters	103,0
1 cup milk, skimmed	85.0
1 large egg, boiled	26.0
1 slice cheddar cheese	15.0
100 g shrimp, cooked	14,5
100 g canned tuna in water	8,0

Selenium

Selenium is incorporated into proteins called selenoproteins, which are important antioxidant enzymes. The antioxidant properties of these proteins help prevent cell damage from free radicals. Selenium, due to its strong antioxidant action, appears to contribute to the proper functioning of the thyroid gland.

The European Food Safety Authority (EFSA) recommends for adults a daily adequate intake of 70 μg for selenium. ²

Good dietary sources of selenium include:

• Nuts (especially Brazil nuts)

• Animal products, such as meat, poultry, fish, and seafood

• Grains

• Dairy products

The table below shows some foods and the amount of selenium they contain. ³

Food	Amount of Selenium (μg)
30 g Brazil nuts	544,0
100 g tuna, cooked	102,2
100 g beef steak, grilled	36,7
100 g turkey, roasted	34,5
100 g chicken, roasted	24.4
1 cup brown rice, cooked	19.0
1 large egg, boiled	15.0
1 slice whole wheat bread	13.0

Zinc

Zinc is a trace element essential for the synthesis of thyroid hormones. Zinc deficiency appears to be associated with the occurrence of hypothyroidism.

Therefore, it is important that our diet meets the recommended daily intake for zinc.

The European Food Safety Authority (EFSA) recommends a daily adequate intake of 9.4 mg and 7.5 mg of zinc for adult men and women, respectively.

Zinc is mainly found in foods of animal origin such as:

• Red meat

• Poultry

• Seafood

There are also good plant sources of zinc, such as legumes and whole grain products. However, these foods contain phytic acids that inhibit the absorption of zinc, making them less effective sources of this mineral.

Goitrogenic Substances

This term is used to describe compounds found primarily in cruciferous vegetables and soy, which appear to lead to reduced synthesis of thyroid hormones.

Cruciferous vegetables include: broccoli, cauliflower, cabbage, Brussels sprouts, and turnips.

In the past, it was recommended that people with hypothyroidism avoid consuming these vegetables, as there was a risk of disrupting thyroid hormone levels.

However, recent randomized studies have failed to show significant changes in blood thyroid hormone levels due to the consumption of these vegetables. Therefore, the consumption of these vegetables should not be discouraged for people with hypothyroidism, as long as it’s not excessive.

Regarding soy products, such as soy milk, tofu, and soy sauce, they contain isoflavones, substances that inhibit the action of thyroid peroxidase, which is essential for the synthesis of thyroid hormones.

For this reason, it was previously theorized that soy consumption could increase the risk of hypothyroidism.

According to more recent studies, however, high soy consumption in individuals with normal thyroid function and in those with subclinical hypothyroidism caused minimal increases in TSH and no change in free thyroxine levels.

Therefore, moderate soy consumption is absolutely safe for people with hypothyroidism.

Conclusion

The thyroid is one of the most important endocrine glands, and its proper function is essential for ensuring our good health.

The thyroid gland produces thyroid hormones, with T3 (triiodothyronine) and T4 (thyroxine) being the most important, which have significant effects on various cells and organs in our body. For this reason, problems with the thyroid gland can affect most functions in the human body.

One of the most common thyroid disorders is hypothyroidism, a condition characterized by the thyroid gland’s inability to produce sufficient amounts of the thyroid hormones T3 and T4.

Although there is no single specific diet for people diagnosed with hypothyroidism, a proper and balanced diet that ensures adequate intake of specific nutrients plays a crucial role in the proper functioning of the thyroid gland.

Bibliography

1. NHS. Iodine Available at: https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/. (Accessed August 2023)

2. EFSA. Scientific Opinion on Dietary Reference Values for Selenium. EFSA Journal 2014;12(10):3846. Doi 10.2903/j.efsa.2014.3846.

3. NHS. Selenium. Available at: https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/ . (Accessed August 2023).

Frequently Asked Questions

What is the Thyroid Gland?

The thyroid is a small endocrine gland located in the front part of the neck that is responsible for producing and releasing hormones in our body.

The main hormones of the thyroid gland are T4 (thyroxine) and T3 (triiodothyronine). Their primary function is to regulate metabolism. However, they affect every organ and cell in our body, ensuring a multitude of functions, from normal heart function to heat production and good digestive health.

What is Hypothyroidism?

Hypothyroidism is one of the most common thyroid gland disorders, characterized by reduced production of thyroid hormones.

Their reduced secretion results in the appearance of symptoms, with the most common being: fatigue, weight gain, dry skin, sensitivity to cold, decreased reflexes, concentration – memory – thinking disorders, depression, drowsiness, constipation, menstrual disorders, reduced fertility, bradycardia, myxedema.

Is There an Ideal Diet for Hypothyroidism?

The truth is that there is no ideal diet that can replace thyroid medication. In other words, diet cannot function as a therapeutic tool in people diagnosed with hypothyroidism.

However, the value of diet for good thyroid health should not be underestimated, as there are specific nutrients that are essential for its proper function.

Therefore, adopting a proper diet that provides us with all those essential nutrients plays an important role in ensuring good thyroid function.

Are There Nutrients That Have Been Linked to Thyroid Health?

There are certain nutrients that have been linked to thyroid health. The most well-known trace element associated with thyroid health is iodine, as it is essential for the synthesis of thyroid hormones. Additionally, adequate selenium intake appears to play an important role in thyroid gland function. Another nutrient that has been linked to thyroid function is zinc, with zinc deficiency being associated with the development of hypothyroidism.

Are there foods that should be avoided if someone has hypothyroidism?

In the past, there was a belief that certain substances (goitrogens) found in foods, such as cruciferous vegetables and soy, could lead to reduced synthesis of thyroid hormones and therefore should be limited in the diet of individuals with hypothyroidism.

However, newer data suggest that the consumption of these foods should not be discouraged for people with hypothyroidism, as long as they are not consumed in excess.