Important: This page is for informational purposes only, based on published peer-reviewed research and official UK dietary guidelines (NHS, EFSA, SACN). It does not constitute medical advice. Always consult your GP or pharmacist before starting, stopping, or combining supplements.
Iodine — Forms, Dosage & Interactions
Also known as: potassium iodide, kelp iodine, iodide, nascent iodine
Overview
Iodine is an essential trace mineral the body cannot synthesise, making adequate dietary intake — and supplementation where required — necessary for normal physiological function. Its primary role is in the synthesis of thyroid hormones thyroxine (T4) and triiodothyronine (T3), which govern metabolic rate, thermoregulation, growth, and neurological development. Despite its importance, iodine deficiency is not confined to developing regions; survey data indicate mild-to-moderate deficiency is common in the UK population, particularly among women of reproductive age, those following vegan or dairy-free diets, and adolescents. The UK's lack of a mandatory salt iodisation programme means dietary iodine relies heavily on dairy, seafood, and eggs — foods absent or limited in increasingly popular dietary patterns. Supplementation is most relevant for individuals with restricted dietary intake and pregnant women, for whom adequate iodine is critical for foetal brain development. The NHS sets the UK RDA at 150 mcg per day. The overall evidence base for iodine's role in thyroid health is rated strong; evidence linking corrected deficiency to cognitive outcomes, particularly in pregnancy, is also well-established. Individual responses to supplementation may vary.
UK Dosage Guidelines
| Guideline | Value | Source |
|---|---|---|
|
Reference Nutrient Intake (RNI)
The amount sufficient for most people |
150 mcg | NHS / SACN |
|
Tolerable Upper Level (UL)
Maximum daily intake unlikely to cause harm |
600 mcg (EFSA) | EFSA / SACN |
Forms Comparison
Iodine is available in several supplemental forms. Bioavailability and suitability vary.
| Form Name | Bioavailability | Notes |
|---|---|---|
| Potassium Iodide | high | Standard supplemental form, well-absorbed |
| Kelp-derived Iodine | moderate | Natural source but iodine content can vary significantly between batches |
When to Take Iodine
Recommended Time
☀️ Morning — research suggests taking Iodine in the morning
Additional Notes
Morning with food. Common deficiency in UK — dairy and fish are main dietary sources.
With or Without Food
Research suggests taking Iodine with food for better absorption.
Known Interactions
2 known interactions with other supplements.
Selenium and iodine work together in thyroid function. Research indicates selenium-dependent deiodinase enzymes are essential for converting T4 to the active T3 thyroid hormone.
Action: Both nutrients support thyroid health. Supplementing iodine without adequate selenium may be counterproductive, as selenium protects the thyroid from oxidative damage during hormone synthesis.
Read full analysis →Iron deficiency can impair thyroid function and iodine utilisation. Research suggests that iron deficiency reduces the effectiveness of iodine supplementation for thyroid health.
Action: Addressing iron deficiency alongside iodine supplementation may improve thyroid outcomes. Both can generally be taken at the same time.
Read full analysis →Top Iodine Products on AIScored
Nutriburst Biotin Beauty - Healthy Hair, Skin & Nails - Vegan Gummies • 2500mcg Biotin with Zinc, Iodine, Vitamins A, C, D3 & E - Mixed Berry Flavour • Sugar Free
Check interactions with your other supplements
Add Iodine to our interactive Stack Analyzer and see how it works with everything else you take.
Add Iodine to your stack →Related Ingredients
Frequently Asked Questions
Research suggests women of reproductive age — particularly those avoiding dairy — face the greatest risk. Vanderpump et al. (2011, The Lancet) found that over two-thirds of UK schoolgirls surveyed had urinary iodine concentrations consistent with mild deficiency. Those following vegan diets are especially vulnerable, as plant-based foods are generally low in iodine. Pregnant women represent another at-risk group given elevated demands during foetal development. Individual responses may vary.
Yes. EFSA sets the tolerable upper intake level at 600 mcg per day for adults. Sustained excess may paradoxically impair thyroid hormone synthesis via the Wolff-Chaikoff effect and, in susceptible individuals, may trigger or exacerbate autoimmune thyroid conditions. A review by Leung and Braverman (2014, Nature Reviews Endocrinology) outlines the clinical consequences of iodine excess, including thyroiditis and hypothyroidism. People with existing thyroid conditions should seek medical advice before supplementing.
Research indicates adequate iodine during pregnancy is critical for foetal neurological development. Bath et al. (2013, The Lancet) found that mild iodine deficiency in UK pregnant women was associated with lower verbal IQ and reading scores in children assessed at ages 8 and 9. NHS guidance recommends pregnant women ensure sufficient intake. Many licensed pregnancy supplements now include iodine at or near the 150 mcg RDA. Individual needs during pregnancy vary and personalised medical guidance is advised.