Iodine is an essential trace element and has to be taken in with the diet. The amount of iodine in food depends on the concentration of this trace element in the soil. Iodine deficiency therefore often depends on a person’s home region and the iodine content of the consumed food.
Iodine deficiency can lead to malfunctions of the thyroid, and to growth disorders in embryos, children and adolescents. People at risk of insufficient iodine intake include pregnant women and growing children, as well as people living in areas with iodine deficient soil.
Despite the fact that iodine deficiencies could easily be prevented, eg by iodine fortified salt, insufficient iodine supply remains the leading cause for brain damage and developmental disorders, according to the WHO.
What are the functions of iodine?
- Iodine is essential for the thyroid gland: Iodine regulates the production of the thyroid hormones T3 (triiodothyronine) and T4 (thyroxine), controlling their functions throughout the body.
- Iodine is critical for development: Iodine significantly contributes to organ and brain formation during child development.
- Iodine regulates the metabolism: Thyroid hormones regulate fat production and absorption. Iodine deficiency can lead to increased levels of cholesterol and metabolic disorders.
- Iodine strengthens the skeletal system: Thyroid hormones support bone formation and muscle function.
- Iodine can protect from cancer: Iodine can attenuate the growth of tumour cells, and contribute to their cell death (apoptosis).
Iodine deficiency – what causes it and what are the symptoms?
Iodine deficiency occurs due to insufficient uptake of iodine with the diet. People living on iodine deficient soil are at increased risk of developing iodine deficiencies. Common areas of iodine deficiency are mountainous regions such as the Alps, Himalaya, Andes, as well as river valleys in south and southeast Asia, and arid areas in Africa.
Iodine deficiency is classified as a widespread health risk in 118 countries, and affects more than 1.5 million people worldwide. Iodine deficiency can lead to iodine deficiency disorders (IDD).
- Thyroid enlargement (goitre)
- Decreased concentration and attention span
- Memory decline
- Delayed reaction capacity
- Reduced mental capacity and endurance
- Fatigue and exhaustion
- Constipation and weight gain
- Dry skin and brittle nails and hair
- Reduced fertility and menstrual disorders
- Hormonal imbalances
- Speech disorders
- Loss of hearing
Iodine dosage recommendations
The recommended daily intake depends on age, with special recommendations for pregnancy and lactation period. There is little international agreement on recommended daily allowances, with discrepancies even between neighbouring countries such as Switzerland and Germany. There is, however, common consent that under- as well as oversupply of iodine is detrimental. 
Daily intake in micrograms (µg), as recommended by the German Society for Nutrition (Deutsche Gesellschaft für Ernährung, DGE):
- New-borns up to 4 months: 40 µg/day
- Babies from 5 to 12 months: 80 µg/day
- Children from 1 to 3 years: 100 µg/day
- Children from 4 to 6 years: 120 µg/day
- Children from 7 to 9 years: 140 µg/day
- Children from 10 to 12 years: 180 µg/day
- Children:13 to 14 years: 200 µg/day
- Adolescents and adults: 15 to 51 years: 200 µg/day
- Adults over 51: 180 µg/day
- Pregnancy - 230 µg/day
- Lactation - 260 µg/day
Who needs iodine?
The body is unable to produce iodine on its own, therefore depending on daily dietary intake. People living in areas with iodine deficient soil are at a particular risk of developing IDD. Europe is still considered an area with high prevalence of iodine deficiencies.
Sufficient intake of iodine is especially important during pregnancy, as undersupply during this period can have dramatic consequences for the early development of the child. Iodine is of critical importance during the entire developmental phase to support healthy growth and mental development of the child.
Iodine is essential for the thyroid gland
The main tasks of the thyroid gland are storage of iodine and production of thyroid hormones. These regulate important bodily functions and play a major role during the neuronal and mental development, as well as during sexual maturation.
Iodine regulates cell growth and migration, particularly in the brain. Thyroid hormones further control energy and fat metabolism, and could even be involved in the immune system. Reduced activity of the thyroid due to insufficient iodine intake can thus affect the entire body.
Iodine is critical for development
Iodine plays a crucial role during pregnancy and/or the early child development for formation of the organs, particularly the brain. Insufficient iodine supply and low thyroid hormone production during this time can negatively affect the development of the heart, liver, kidney, muscles and the brain. Downstream consequences depend on the extent of the deficiency and can reach from reduced cognitive abilities and growth inhibition during childhood to severe organ and brain impairment.  
Iodine regulates the metabolism
Iodine-regulated thyroid hormones are actively involved in cholesterol synthesis. A study from Michigan State University showed that persons with iodine deficiency frequently have increased cholesterol levels (LDL), typically associated with hyperthyroidism. The elevated LDL levels were often reduced to normal levels after treatment of hyperthyroidism.
These results indicate active regulation of the fat metabolism by iodine. Correction of iodine deficiency could therefore in specific cases lead to weight loss, as well as to reduction of cardiovascular risk.
Iodine strengthens the skeletal system
Due to its regulation of the thyroid hormones, iodine directly influences muscle and bone formation and regeneration. Iodine deficiency in turn leads to growth inhibition, often associated with selenium deficiency.
Enzymes activated by iodine during muscle development could enhance treatment of degenerative muscle disorders.
Iodine can protect from cancer
Other organs besides the thyroid gland are also able to store iodine. These include prostate and breast, as well as the pancreas, the nervous system and the gastrointestinal system.
In all organs in which it is present, iodine inhibits cell growth of benign as well as malignant tumours. These abilities make iodine a potential active agent to protect from cancer or to combat it.
Iodine in food
Iodine is present in all animal foodstuffs, as well as in vegetables, water, and sea salt. In animal and plant derived products iodine content depends on the concentration of iodine in the soil and feed, respectively. Iodine fortified table salt represents one of the most important sources of iodine.
Other rich sources of iodine include sea fish, dairy products, eggs, cereals, and green vegetables such as spinach and broccoli. Several types of vegetables such as cabbage, cauliflower and radish however belong to the so called goitrogenic products, which can inhibit iodine uptake and contribute to the development of iodine deficiency.
Iodine side effects
Iodine is an essential trace element that needs to be taken in in sufficient amounts. Excessive supplementation of iodine can however be detrimental to health and should be avoided.
Iodine excess can cause symptoms similar to those of iodine deficiency. In addition, too much iodine can contribute to inflammation of the thyroid and to thyroid cancer.
The recommended upper limits of iodine are age dependent:
- Children up to 3 years - 200 µg
- Children from 4 to 8 years - 300 µg
- Children from 9 to 13 years - 600 µg
- Adolescents from 14 to 18 years - 900 µg
- Adults - 1100 µg
Excluded from these recommended upper limits are persons who are taking higher amounts of iodine for medical reasons and under strict supervision.
Iodine interactionsBased on its biochemical and pathophysiological properties, iodine can interact with several substances and impact on their effect.
- Medication for the treatment of hyperthyroidism – excess intake of iodine can inhibit the production of thyroid hormones.
- Blood pressure regulators, specifically ACE inhibitors – intake of iodine in the form of potassium iodide can dramatically increase the concentration of potassium in the blood.
- Diuretics regulating the excretion of potassium – additional intake of potassium iodide can also increase the concentration of potassium here.
In the case of concurrent use of iodine and prescription medication, careful study of the pre leaflet is advised.
Iodine Studies and references
- National Institutes of Health Iodine
- World Health Organization Iodine deficiency disorders
- Kapil U. Health Consequences of Iodine Deficiency. Sultan Qaboos Univ Med J. 2007;7(3):267-272.
- Delange F. The Disorders Induced by Iodine Deficiency. Thyroid. 1994;4(1):107-
- Vitti P, Rago T, Aghini-Lombardi F. Iodine deficiency disorders in Europe. Public Health Nutr. 2001 Apr;4(2B):529-35.
- Rohner F, Zimmermann M, Jooste P. Biomarkers of Nutrition for Development - Iodine Review. J Nutr. 2014;144(8):1322S-1342S.
- Deutsche Gesellschaft für Ernährung e.V. Jod - empfohlene Zufuhr.
- Taylor PN, Okosieme OE, Dayan CM. Therapy of endocrine disease: Impact of iodine supplementation in mild-to-moderate iodine deficiency: systematic review and meta-analysis. Eur J Endocrinol. 2013 Oct 2;170(1):R1-R15.
- Lee KW, Shin D, Song WO. Low Urinary Iodine Concentrations Associated with Dyslipidemia in US Adults. Nutrients. 2016;8(3):171.
- Moreno-Reyes R, Egris D, Boelaert M. Iodine Deficiency Mitigates Growth Retardation and Osteopenia in Selenium-Deficient Rats. J. Nutr. 2006;136(3):595-600.
- Salvatore D, Simonides WS, Dentice. Thyroid hormones and skeletal muscle - new insights and potential implications. Nat Rev Endocrinol. 2014;10(4):206-214.
- Aceves C, Anguiano B, Delgado G. The Extrathyronine Actions of Iodine as Antioxidant, Apoptotic, and Differentiation Factor in Various Tissues. Thyroid. 2013;23(8):938-946.