Iodine
Needed for thyroid hormone. Seaweed sources it, but the dose is unpredictable.
Iodine is required to make thyroid hormone, which regulates metabolism throughout the body, and requirements rise during pregnancy to support the baby's thyroid development. Potassium iodide is the standard supplement form with consistent, predictable dosing. Kelp and seaweed-derived iodine are natural sources, but their iodine content varies considerably between products and batches, which makes precise dosing difficult and is why UK guidance flags seaweed as a source to use cautiously rather than to rely on for a specific intake.
Reference values
Daily reference values from official nutrition authorities. These are population reference figures, not personal recommendations.
| RDA | Upper limit | Source |
|---|---|---|
| 140 mcg | 600 mcg | UK SACN DRVs (1991); SACN Iodine and Health (2014) — 140mcg/day adults; EFSA UL 600mcg/day (2006) |
| 140 mcg | 600 mcg | UK SACN DRVs (1991); SACN Iodine and Health (2014) — 140mcg/day adults; EFSA UL 600mcg/day (2006) |
Forms and bioavailability
Not all forms are absorbed equally. The form on your supplement label affects how much your body can actually use.
| Form | Absorption | With food | Timing | Evidence |
|---|---|---|---|---|
| Potassium iodide | Typical | With food | Morning | Strong |
| Kelp / seaweed-derived iodine | Lower | With food | Morning | Informational |
How it pairs with other supplements
Works well with
Selenium and iodine work together in thyroid hormone synthesis: selenium-dependent deiodinases convert T4 to active T3, and selenoperoxidase protects the thyroid gland from oxidative damage during hormone synthesis. Supplementing iodine without adequate selenium in iodine-deficient populations may worsen autoimmune thyroiditis.
Stack Almanac tracks your iodine source and totals your intake against the UK reference value, including the higher figure recommended during pregnancy, and surfaces the selenium pairing that supports healthy thyroid hormone conversion.
Track your Iodine in Stack Almanac
Last reviewed: 2026-07-08. Reference values are adult-general RDAs from UK. Individual needs may vary. This page is for informational purposes only and is not a substitute for professional medical advice.