What are reliable dietary sources of iodine besides iodized salt and how much do they contribute?
Executive summary
Reliable dietary iodine comes mainly from marine foods (seaweed and many fish/shellfish), animal products (milk, yogurt, cheese and eggs), and some fortified foods such as breads made with iodate dough conditioners; the exact contribution of any item varies widely by species, farming/processing practices and geography, but single typical portions of several of these foods can supply a substantial fraction — or in some cases exceed — the 150 µg daily value (DV) for adults [1] [2] [3].
1. Seaweed and seafood: the heavyweight sources — highly variable but often enough alone
Seaweed is among the richest natural sources of iodine and certain seaweeds can deliver well above the 150 µg adult DV in a single serving; for example, nori averaged 116 µg per 5 g serving in USDA-linked analyses but values differ by species and origin, and some kelps (kombu) can contain far larger amounts, so both deficiency and excess are possible depending on type and portion [2] [4]. Saltwater fish and many shellfish are also dependable contributors: the USDA/FDA/NIH collaborative database shows iodine in seafood ranging from only a few micrograms per 100 g in some freshwater species to roughly 227 µg/100 g in haddock, translating to per‑serving iodine that can range from under 5 µg to nearly 250 µg depending on species and portion size [2] [1].
2. Dairy and eggs: steady background contributors shaped by farming and processing
Milk, yogurt, cheese and eggs are repeatedly identified across public health sources as “good” sources of iodine and — in many countries — the primary contributors to population iodine intake; dairy can account for roughly 12–53% of daily iodine intake in European assessments because farm practices (iodine‑fortified feed, iodophor disinfectants) raise milk iodine content beyond soil levels [5] [6]. A single egg provides on the order of ~25 µg of iodine (about 17% of the DV) according to analytical tables and reviews, so routine consumption of eggs and dairy builds steady intake even if each item supplies less iodine than a seaweed or fatty fish portion [5] [1].
3. Fortified bread and other added sources: intermittent but sometimes large contributors
In places where iodate dough conditioners are used, a single slice of white bread can contain up to roughly 185 µg of iodine, meaning fortified bread alone can meet or exceed daily needs for some consumers [7] [3]. However, iodate use is not universal — about 20% of certain U.S. bread labels listed iodate in recent branded‑food data — and food labels are not required to list iodine unless it’s added, so fortified bread’s contribution is important but inconsistent across brands and regions [3] [7].
4. Quantifying “how much” — examples that show the range
Practical portion examples from the sources illustrate the range: a 3‑ounce portion of cod has been reported in different sources at roughly 99–146 µg iodine, covering two-thirds to nearly the full DV in one serving; shrimp gives smaller but meaningful amounts (Healthline cites ~23% of the DV from a 3‑ounce serving, roughly 35 µg), while some fish (e.g., haddock) can deliver up to ~250 µg per serving according to USDA data — and typical seaweed servings may exceed recommendations and risk excess if consumed frequently [8] [9] [4] [2] [3].
5. Variability, risk groups and labeling limits: why counts matter
The defining theme across the evidence is variability: soil iodine, seaweed species, fish species, animal feed, dairy sanitation practices and manufacturer choices (iodate in bread) all drive wide ranges in iodine content, and nutrition labels usually do not list iodine unless it was added — so consumers cannot reliably estimate intake from labels alone [3] [2] [1]. Public health sources flag pregnant people, those who avoid dairy/seafood (including many vegans), and populations not using iodized salt as groups at higher risk of inadequate intake, while those eating large amounts of certain seaweeds risk excessive iodine [1] [10] [5].
6. Practical takeaway: mix sources and, for special situations, consult guidance
Combining modest portions of seafood, dairy and eggs or consuming fortified bread can meet the 150 µg DV without iodized salt in most cases — for example, one 3‑ounce serving of many cod or haddock variants or a fortified bread slice can supply the DV, while eggs and dairy offer reliable background amounts — but the exact contribution depends on food choice and origin, and pregnant people or those on restricted diets should check supplements or professional advice because dietary patterns and regional data show gaps [8] [7] [5] [1].