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Iodine (I)

Iodone is an essential trace element. An adult contains around 20-50 micrograms of iodine with 2/3 of the total supply being stored in the thyroid gland. The only known function of iodine is that it supports the two thyroid hormones that control all metabolic processes in the body. The thyroid hormones are named T3 (triiodothyronine) and T4 (thyroxine), depending on how many iodine atoms they contain. T3 functions substantially faster than T4, which is considered a precursor. Selenium is also an essential constituent of enzymes that regulate thyroid hormonal activity. Among other things, it works by removing an iodine atom, whereby the passive T4 hormone is converted to the active T3 hormone. If too little T3 hormone is produced, the metabolic rate slows down. If too much T3 is produced, the metabolic rate speeds up. For that reason, it is vital that there is enough iodine and selenium to ensure the right balance.

Functions and importance for

  • The two thyroid hormones T3 and T4
  • The body's metabolism
  • Child growth
  • Energy turnover
  • Weight control

Deficiencies and poor utilisation may be caused by

  • Insufficient diet (especially if it lacks fish and shellfish)

Deficiency symptoms

  • Goiter (enlarged thyroid gland)
  • Low metabolism accompanied by fatigue, slow heart rate, chills, and weight gain.
  • In rare cases, hyperthyroidism (increased metabolic rate) accompanied by heart palpitations, unrest, elevated blood pressure, increased appetite, and weight loss.
  • Children: Goiter, dwarfism, or mental retardation
  • Pregnancy: Fetal damage


Mainly maritime sources like seaweed, fish, shellfish, fish sauce, oyster sauce, and sea salt. Other sources are dairy products and eggs.
A good way of preventing goiter is to add iodine to table salt. Iodine-enriched salt is also found in bread from bakers and industrially baked bread.

Iodine content in micrograms per 100 grams

Seaweed 36,000
Mussels 140
Salmon 65
Whole eggs 21
Fruit and vegetables 0.2-1

Recommended daily allowance (RDA)

Adults: 11 years of age and older: 150 micrograms
Children: 1-10 years of age: 70 micrograms
Pregnancy and lactation: 175 and 200 micrograms (respectively)

Increased need

  • Growing children
  • Elderly people
  • Pregnant women
  • Vegetarians and vegans

Important information

It is possible to have goiter and hypothyroidism (low metabolism) without being iodine deficient. Thyroid problems may also be caused by lack of selenium, which is needed to regulate the thyroid hormones.
Heating reduces the iodine content in food.

Overdosing - side effects

Humans can tolerate relatively large quantities of iodine. However, prolonged intake of excessive amounts may block the production of thyroid hormones and cause hyperthyroidism (too high metabolic rate) or hypothyroidism (too low metabolic rate). Pregnant and lactating women should be particularly careful, as an overdose may impair the thyroid function of the child.

Weight loss pills that contain large amounts of iodine may harm the hormonal balance in the long run.

Radioactive iodine (e.g. after nuclear disasters) may accumulate in the thyroid gland and cause serious damage and cancer. The damage can be limited by taking iodine tablets (potassium iodide)