Two trace elements are essential for a healthy thyroid: iodine and selenium.

Iodine and thyroid

Most of the iodine present in the body is found in the thyroid, where it is essential for the production of the thyroid hormones that have a key role in various important processes, like the metabolism of sugars and fats and body temperature, as well as the development and growth of many organs and tissues, such as the central nervous system and the musculoskeletal system, during both pregnancy and childhood.

Food is the main source of iodine in nature, for example fish contains 100-300 mcg/100 g, milk 15 mcg/100 mL, eggs 8 mcg/100 mL and cereals 6 mcg/100 g. The iodine present in food is readily absorbed by the stomach and duodenum and once it has been absorbed it enters the bloodstream and is used by the thyroid to produce thyroid hormones. Although our body is able to eliminate excess iodine through urine, an excessive iodine intake can be harmful for health.

Iodine and the thyroid

How much iodine should we take?

The recommended daily iodine intake for an adult is approximately 150 micrograms (mcg), according to European reference values. However, iodine requirements change with age and the phases of life, for example during pregnancy and breastfeeding, when the recommended daily iodine  amount increases to about 200 micrograms.


IODINE: Recommended daily allowances (RDA)

Infants 7-11 months

70 mcg

Children 1-10 years

90 mcg

Children 11-14 years

120 mcg

Adolescents 15-17 years

130 mcg

≥ 18 years

150 mcg


200 mcg


200 mcg

What happens if we don’t take enough amount of iodine?

An insufficient iodine intake can prevent the thyroid from producing sufficient quantities of thyroid hormones, which can lead, during all stages of life, to the development of iodine-deficiency disorders.

The most common consequence of iodine deficiency is goitre, an enlargement of the thyroid, which is the most common symptom of iodine deficiency worldwide and can affect either the whole gland or parts of it, by forming one or more nodules.

If the iodine deficiency persists over time and is not corrected, it is possible to develop hypothyroidism, a disease in which the inadequate production of thyroid hormones can have significant repercussions on health, depending on the severity of the deficiency and the period in which it occurs.

This becomes particularly critical during pregnancy, breastfeeding, and the first three years of life. During these periods it is fundamental to receive adequate amounts of iodine, since a severe deficiency in this element during foetal and neonatal development can cause irreversible damage to the brain and central nervous system, causing mental retardation, and during pregnancy it can cause miscarriage. Even a mild iodine deficiency can cause a minor intellectual deficit, and it is therefore important that pregnant women and children under three years of age have an adequate iodine intake through a balanced diet and iodine supplements in order to avoid deficiencies that could be a threat to normal physical and cognitive development.

insufficient iodine intake

Iodine supplements for thyroid

In cases in which there is an iodine deficiency because this element is not introduced in adequate amounts with the diet, it can be necessary to take iodine supplements; as the synthesis of thyroid hormones depends on the availability of adequate quantities of iodine, most of the supplements used for thyroid health contain this mineral or particularly rich sources of it (such as, for instance, seaweed).

Supplements containing iodine are particularly useful during pregnancy and breastfeeding, since the daily iodine requirement is higher during these phases of life.

It is nevertheless advisable to replace, at all ages, normal salt with iodine-enriched salt in quantities of 3-5 mcg per day.

What about selenium?

Selenium is a trace element that is very common in nature and is another fundamental mineral for the metabolism of thyroid hormones, as well as having important antioxidant properties.

The thyroid is the organ with the highest concentration of selenium in the human body, because here the selenoproteins, proteins containing selenium, are essential for protecting the thyroid from the damage caused by free radicals and inflammation. Moreover, in various tissues these proteins are responsible for converting thyroid hormone into its biologically active form.

Selenium and the thyroid

Selenium requirements

The recommended daily intake of selenium is 55 micrograms for adults, but it is higher in pregnant and breastfeeding women. In children, on the other hand, the requirement is lower and depends on age.


SELENIUM: Recommended daily allowances (RDA)

Infants 1-11 months

15 mcg

Children 1-3 years

15 mcg

Children 4-6 years

20 mcg

Children 7-10 years

35 mcg

Adolescents 11-14 years

55 mcg

Adolescents 15-17 years

70 mcg

≥ 18 years

70 mcg


70 mcg


85 mcg

An excess of selenium can be toxic for the body and can cause a condition known as selenosis, which can present with symptoms like gastrointestinal problems, skin lesions, hair loss and nervous system damage.

Selenium and thyroid

Selenium is the cofactor of various selenoproteins involved in the hormone balance of the thyroid and in protecting the cells from the damage caused by free radicals. Therefore, like iodine deficiency, selenium deficiency can also compromise the synthesis of thyroid hormones and increase the risk of developing diseases of autoimmune origin such as, for example, Hashimoto’s thyroiditis (or chronic autoimmune thyroiditis), which is the most common of all thyroid diseases and the most frequent cause of hypothyroidism. In this case, the role of selenium is to reduce the quantity of auto-antibodies that cause the disease and therefore to support thyroid function. Also in Basedow’s disease, a common cause of hyperthyroidism, selenium supplementation can reduce the auto-antibodies, favour response to antithyroid drugs and, where present, improve eye disorders.

Selenium and the thyroid

Selenium supplements for thyroid

Selenium can be found in nature and in some foods – such as liver, fish, milk and dairy products, walnuts, pulses, rice, and meat – and therefore we take it in with our diet, but it is not always readily absorbable. Furthermore, in recent years, there has been a reduction in the dietary intake of selenium in the European population because, due to the different farming methods used, foods contain less and less of this element, resulting in a selenium deficiency of varying degrees in the different countries.

Therefore, where indicated, it can be useful to take selenium supplements, but it is important to pay attention to the form of selenium they contain. As a matter of fact, organic forms like L-selenomethionine and selenium-enriched yeast are preferable to the inorganic forms like selenite, because they offer better bioavailability.

  • Scientific Opinion on Dietary Reference Values for iodine - EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). EFSA Journal 2014
  • Sorrenti S, Baldini E, Pironi D, Lauro A, D'Orazi V, Tartaglia F, Tripodi D, Lori E, Gagliardi F, Praticò M, Illuminati G, D'Andrea V, Palumbo P, Ulisse S. Iodine: Its Role in Thyroid Hormone Biosynthesis and Beyond. Nutrients. 2021 Dec 14;13(12):4469.
  • Kieliszek M, Bano I. Selenium as an important factor in various disease states - a review. EXCLI J. 2022 Jul 5;21:948-966.
  • Scientific Opinion on Dietary Reference Values for selenium - EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). EFSA Journal 2014;12(10):3846
  • Dietary Reference Values for nutrients - Summary report. Update: 4 September 20191. Volume14, Issue12, December 2017



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