Minerals - Iodine (I)

Question 1

Iodine (I)

Answer 1

• Iodine (I) is a component of thyroid hormones which regulate the metabolic rate of all the cells in the body
• Iodine from food is efficiently absorbed and converted in the GI tract to iodide ions (close to 100% of dietary iodine is absorbed)
• Iodine levels in soil vary widely globally but are relatively low
• The ocean is Earth’s main source of iodine

Question 2

Food sources

Answer 2

Food sources include:
* Sea vegetables (excellent source)
* Ocean fish and shellfish such as cod and scallops
* Iodine is also in eggs and dairy foods (due to the fortification of animal feed) with small amounts in plants depending on the soil

Question 3

Functions: Thyroid hormones

Answer 3

Functions: Thyroid hormones
* Iodine is an essential component of thyroid hormones. ‘T4’ is named to reflect the presence of 4 iodine atoms, and ‘T3’ – 3 iodine atoms
Therapeutic uses:
* Thyroid health (hypothyroidism)

Question 4

Functions: Brain health

Answer 4

Functions: Brain health
* Foetal and infant development: I.e. brain and bone formation during pregnancy
Therapeutic uses:
* Cognitive function during childhood

Question 5

Functions: Metabolism

Answer 5

Functions: Metabolism
* Critical determinant of energy metabolism in cells
Therapeutic uses:
* Reversing slow metabolism

Question 6

Making thyroid hormones

Answer 6

• The thyroid gland ‘traps’ iodine from the blood
• Thyroid hormone is made by binding iodine and the amino acid tyrosine to a glycoprotein called thyroglobulin
• The rate of iodine capture is under the control of TSH (thyroid stimulating hormone)
• The selenium-dependent enzyme, iodothyronine deiodinase converts the relatively inactive T4 to be active T3

Question 7

Deficiency

Answer 7

• In the early 20th century iodine deficiency (ID) ID was common in the UK/IRE and many other countries around the globe
• The ‘iodisation’ of table salt began to be implemented in many countries to reverse ID (ID was addressed by the use of iodine fortified cattle feed and an increase in milk consumption)
• ID leads to decline in thyroid hormone production and if prolonged, it can lead to ‘hypothyroidism’ with symptoms like:
  o Fatigue
  o Weight gain
  o Depression
• Prolonged ID can lead to a goitre (enlarged thyroid).
• Note: Hypothyroidism can occur without ID; e.g. Hashimoto’s thyroiditis (autoimmune)
• Severe ID during pregnancy causes extreme and irreversible mental and physical retardation (a daily intake of 150 mcg is recommended by the World Health Organization)
• Children with even mild iodine deficiency have goitres and perform poorly at school; with treatment, mental performance improves

Question 8

Toxicity

Answer 8

• Acute iodine poisoning is rare and only occurs with doses of many grams (TUL is 600 mcg)

Question 9

Nutrient interactions

Answer 9

• Consumption of goitrogenic foods such as soya, millet and raw brassica vegetables may interfere with iodine uptake – however, this typically does not have a major clinical effect unless with co-existing iodine deficiency
• Hypothyroidism may also be associated with suboptimal Se status – iodine and selenium deficiencies often overlap
• Additionally, people with hypothyroidism often have suboptimal levels of Zn, Fe, Cu which can exacerbate iodine deficiency
• Nutrients such as tyrosine, Zn, Mg and B vitamins are crucial for iodine utilisation
  Goitrogens = substances in food that interfere with iodine uptake in thyroid

Question 10

Functions

Answer 10

Thyroid hormones
Brain health
Metabolism