Iodine Dosage: RDA 150mcg, Pregnancy 220-290mcg, 1,100mcg Upper Limit

By Erin Rose · Updated July 19, 2026 · Methodology

Educational summary — not medical advice. Iodine affects thyroid function directly at both too-low and too-high intake. Anyone with thyroid disease, nodules, or antibodies should not self-supplement beyond the RDA without a clinician. This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.

The number line: deficiency, RDA, population sweet spot, and the UL

Laid out in order: intake below 10–20mcg/day produces hypothyroidism, frequently with goiter — the earliest clinical sign of inadequate status (NIH ODS). The adult RDA is 150mcg/day; it rises to 220mcg in pregnancy and 290mcg during lactation, reflecting the added demand of fetal and infant thyroid hormone production. Zimmermann 2009's population-level recommendation of 150–250mcg/day sits inside that RDA-to-UL band, not hugging either edge — it's the range associated with the lowest thyroid-disease risk at a population level, echoing the low point of the U-shaped curve described on the hub. The upper limit is 1100mcg/day for all adults, including pregnant and lactating women. Above that, chronic excess starts to carry real, mechanistically-explained risk — not a vague "high doses might be bad" caveat, but two specific, named failure modes.

Why "more" specifically backfires here: Wolff-Chaikoff and Jod-Basedow

The thyroid normally holds hormone output steady across a wide range of iodine intake via the sodium-iodide symporter (Bürgi 2010). When iodine intake spikes acutely, the thyroid temporarily blocks its own hormone synthesis — the Wolff-Chaikoff effect — and in most people, this resolves within days as the symporter downregulates and normal hormone production resumes (the "escape"). But in susceptible individuals — people with pre-existing thyroid disease, a history of iodine deficiency, or an autoimmune predisposition — that escape fails, and the block becomes chronic iodine-induced hypothyroidism. Separately, and through a different mechanism entirely, excess iodine can trigger Jod-Basedow hyperthyroidism in people who have nodular goiter containing thyroid nodules with autonomous TSH-receptor mutations — those nodules, once given abundant iodine substrate, can overproduce thyroid hormone independent of normal regulation. Two named, opposite failure modes, in two different vulnerable populations, both triggered by the same thing: iodine intake well above what the thyroid is built to handle. Chronic high iodine intake is also independently linked to promoting autoimmune (Hashimoto's) thyroiditis by increasing thyroglobulin immunogenicity (Hu & Rayman 2017) — see deficiency vs. excess for the full picture.

How to think about the dose you actually pick

• 150mcg/day is the honest default — it's the RDA for most adults, and most people in iodine-sufficient countries already meet it from iodized salt, dairy, and seafood without a supplement at all.
• Higher is not shown-safer. Zimmermann's 150–250mcg population range is the sweet spot, not a floor to build up from — pushing toward the 1100mcg upper limit "just in case" has no support in this evidence base and real, mechanistically-explained downside risk.
• Pregnancy and lactation raise the RDA, not a license to megadose. 220mcg (pregnancy) and 290mcg (lactation) are still well inside the RDA-to-UL band — see iodine and pregnancy for the full deficiency-risk case.
• "Iodine protocol" doses (12.5–50mg/day) are a different universe entirely — 85–330× the RDA, not studied in the deficiency/pregnancy literature this page is built on, and not recommended. See why, in detail.
• Kelp is not a precise dosing vehicle. Look for a disclosed mcg-per-serving figure — see best iodine for which products actually state it.

Frequently asked questions

Related

• Iodine: what the evidence shows
• Best iodine — ranked by dose-category fit, then cost
• Iodine and pregnancy
• Deficiency vs. excess — the full U-shape synthesis
• Selenium dosage guide — the co-dependent thyroid nutrient

Sources