What Is Iodine and How Does It Work?
Iodine is an essential trace mineral — one that the body cannot synthesise and must obtain from food or supplements. Its primary and critical role is as a structural component of thyroid hormones: triiodothyronine (T3) and thyroxine (T4). These hormones regulate basal metabolic rate, protein synthesis, bone development, and neurological development — processes that are fundamental across all life stages.
The thyroid gland actively concentrates iodine from the bloodstream to produce T3 and T4. When dietary iodine is insufficient, the thyroid compensates by enlarging (goitre) in an attempt to capture more iodine from a limited supply. Prolonged severe deficiency leads to hypothyroidism — clinically characterised by fatigue, weight gain, cold intolerance, and cognitive slowing.
What the Evidence Shows
Iodine Deficiency Is a Public Health Issue in Europe
Contrary to assumptions, iodine deficiency remains relevant in parts of Europe, including Scandinavia and the Baltic region. WHO and UNICEF data indicate that European populations relying primarily on non-iodised salt and low sea-food diets may have suboptimal iodine intake. Estonian national nutrition surveys have documented insufficient iodine intake in certain demographic groups, particularly women of reproductive age.
Impact of Supplementation on Thyroid Function
In populations with confirmed deficiency, iodine supplementation reliably normalises thyroid function markers. A systematic review found that iodine supplementation in mildly deficient populations significantly reduced goitre prevalence and improved thyroid hormone profiles (Zimmermann, 2009). Effects are most pronounced and important in deficient individuals; in iodine-replete individuals, supplementation offers no additional thyroid benefit and may even be harmful at high doses.
Cognitive and Developmental Effects
Adequate iodine during pregnancy is critical for foetal brain development. Studies in pregnant women from mildly iodine-deficient regions show associations between iodine supplementation and improved child cognitive outcomes (Bath et al., 2013). This is one of the most evidence-supported applications of iodine supplementation.
Effect Sizes and Who Benefits
The clearest benefits of iodine supplementation apply to:
- People with documented or likely iodine deficiency (confirmed by low urinary iodine excretion)
- Pregnant and breastfeeding women in regions with low iodine
- Vegans and strict vegetarians who avoid dairy, eggs, and seafood (the main dietary sources)
- Those using non-iodised salt exclusively
For the general population with adequate dietary iodine intake, additional supplementation provides no added thyroid benefit and carries a risk of inducing autoimmune thyroid dysfunction at high doses (Zimmermann & Boelaert, 2015).
EFSA-Approved Claims
EFSA has approved multiple health claims for iodine, reflecting its established essential nutrient status:
- Iodine contributes to normal cognitive function
- Iodine contributes to normal energy-yielding metabolism
- Iodine contributes to the normal functioning of the nervous system
- Iodine contributes to the normal production of thyroid hormones and normal thyroid function
- Iodine contributes to the maintenance of normal skin
These are among the most extensively supported approved claims in the EU nutrition claim system — iodine is an essential nutrient with clear biochemical functions that are absent when it is deficient.
The EFSA nutrient reference value (NRV) for iodine is 150 mcg per day for adults. The established tolerable upper intake level (UL) is 600 mcg/day.
Practical Considerations
The recommended dietary intake is 150 mcg/day for most adults, rising to 200–250 mcg/day during pregnancy and lactation. Standard supplemental doses typically provide 100–200 mcg per serving, which bridges common dietary gaps without approaching the upper limit.
OstroVit Iodine Potassium iodide 200mcg 120tabs is available at maxfit.ee in the jood category and kilpnaarme-toetavad-toidulisandid category. It provides iodine in the form of potassium iodide — the standard, well-absorbed form used in most supplements.
Key caution: iodine supplementation is not appropriate for everyone. Individuals with autoimmune thyroid disease (Hashimoto's thyroiditis or Graves' disease) or those already taking thyroid medication should consult a physician before supplementing, as iodine can trigger or worsen autoimmune thyroid flares.
Honest Verdict
Iodine is a genuinely essential nutrient with the strongest possible evidence base — it is required for thyroid hormone production, and deficiency causes well-documented clinical harm. EFSA has approved multiple health claims. The question for most adults is not whether iodine works — it does — but whether they are actually deficient. For the vegan, the pregnant woman in a low-iodine region, or anyone avoiding iodised salt and seafood, supplementation is well-justified. For the iodine-replete adult, additional supplementation offers no benefit and high doses carry risk.
FAQ
How do I know if I am iodine deficient?
The gold standard is a 24-hour urinary iodine excretion test, but spot urinary iodine concentration is more practical and widely used in population surveys. Clinical signs of deficiency (fatigue, cold intolerance, enlarged thyroid, unexplained weight gain) warrant a blood test for TSH and thyroid hormones, along with a urine iodine measurement. Self-diagnosing iodine deficiency without testing is not recommended.
Is iodised salt enough to meet iodine needs?
For most people who consistently use iodised table salt in cooking and at the table, it is often sufficient. However, iodine content in iodised salt varies by country and brand, and people who use primarily sea salt, unrefined salt, or avoid added salt entirely may not meet their iodine needs through salt alone.
Can too much iodine be harmful?
Yes. The EFSA tolerable upper intake level is 600 mcg/day for adults. Chronically excessive iodine intake — particularly above 1,000 mcg/day from all sources combined — can trigger thyroid dysfunction in susceptible individuals, including both hypothyroidism and hyperthyroidism. Standard supplements providing 100–200 mcg are well within safe limits for healthy adults.
References
Zimmermann, M. B. (2009). Iodine deficiency. Endocrine Reviews, 30(4), 376–408. https://pubmed.ncbi.nlm.nih.gov/19460960/
Bath, S. C., Steer, C. D., Golding, J., Emmett, P., & Rayman, M. P. (2013). Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). The Lancet, 382(9889), 331–337. https://pubmed.ncbi.nlm.nih.gov/23706508/
Zimmermann, M. B., & Boelaert, K. (2015). Iodine deficiency and thyroid disorders. The Lancet Diabetes & Endocrinology, 3(4), 286–295. https://pubmed.ncbi.nlm.nih.gov/25591468/
