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Types of Iodine: Forms & Bioavailability

Evidence:Strong
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This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Forms Comparison

FormBioavailabilityBest For
Potassium IodideHighStandard supplementation — stable, well-absorbed, and most studied form
Kelp/Seaweed ExtractVariableWhole-food source — iodine content varies significantly between products
Nascent IodineModerateMarketed as more bioavailable, but limited clinical evidence vs. potassium iodide

Potassium Iodide

Bioavailability: High. Best for: Standard supplementation — stable, well-absorbed, and most studied form.

Kelp/Seaweed Extract

Bioavailability: Variable. Best for: Whole-food source — iodine content varies significantly between products.

Nascent Iodine

Bioavailability: Moderate. Best for: Marketed as more bioavailable, but limited clinical evidence vs. potassium iodide.

Full Iodine Guide

References

  1. ObservationalBath SC, Steer CD, Golding J, Emmett P, Rayman MP (2013). Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children. The Lancet. DOI PubMed
  2. ReviewZimmermann MB, Jooste PL, Pandav CS (2008). Iodine-deficiency disorders. The Lancet. DOI PubMed
  3. ReviewLeung AM, Braverman LE (2014). Consequences of excess iodine. Nature Reviews Endocrinology. DOI PubMed
  4. Meta-analysisEveleigh ER, Coneyworth L, Welham SJM (2023). Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets.. The British journal of nutrition. DOI PubMed
  5. Meta-analysisGreenwood DC, Webster J, Keeble C, Taylor E, et al. (2023). Maternal Iodine Status and Birth Outcomes: A Systematic Literature Review and Meta-Analysis.. Nutrients. DOI PubMed
  6. Azevedo FM, Machamba AAL, Candido AC, Pinto CA, et al. (2023). Correlation Between Drinking Water and Iodine Status: a Systematic Review and Meta-analysis.. Biological trace element research. DOI PubMed
  7. Candido AC, Azevedo FM, Silva DLF, Ribeiro SAV, et al. (2023). Effects of iodine supplementation on thyroid function parameter: Systematic review and meta-analysis.. Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS). DOI PubMed