Primary Dietary Sources of Iodine
The best sources of dietary iodine are dairy products (especially cow's milk), fish and seafood, iodized salt, and eggs, with dairy being the single most important contributor in Western diets. 1
Main Food Sources
Dairy Products (Primary Source)
- Milk and dairy products are the predominant dietary source of iodine in the UK and US, contributing 38% of total iodine intake in non-pregnant adults and 31% in pregnant/lactating women. 1
- One cup of cow's milk provides approximately 39% of daily iodine needs for adult women and 57% for pregnant women. 2
- Iodine content in milk ranges from 152-256 µg/L depending on season and farming practices, with winter and conventional milk containing higher levels than summer and organic milk. 1
- Plant-based milk alternatives (almond, soy, oat) contain only 2% of the iodine found in cow's milk and are rarely fortified, placing consumers at risk for iodine insufficiency. 1, 2
- Cheese averages 15.2 µg/100g, while dairy powders (including whey) average 471.8 µg/100g. 3
Fish and Seafood (Secondary Source)
- White fish (haddock, cod) contains approximately 105 µg/100g, while oily fish contains about 48 µg/100g. 1
- Marine fish contains 6-fold higher iodine than freshwater fish (40-69 µg/100g). 1
- Other seafood (prawns, crab) averages 92 µg/100g. 1
- Fish contributes 11% of iodine intake in non-pregnant UK adults and 24% during pregnancy. 1
- Cooking reduces iodine content by 20% in fried fish, 23% in grilled fish, and 58% in boiled lobster. 1
Iodized Salt (Global Standard)
- Universal salt iodization is the WHO and UNICEF-recommended strategy for iodine deficiency prevention, adopted by over 120 countries globally. 1
- Salt is fortified at 20-40 mg iodine per kg, based on average consumption of 10g daily. 1
- This remains the most cost-effective method for population-wide iodine sufficiency. 1
Other Sources
- Eggs are a significant source, particularly when red food dyes (FD&C Red No. 3) are present. 3
- Seaweed contains extremely variable iodine levels (11-6,118 µg/g dried), which can exceed safe upper limits. 1
- Fortified foods (bread, biscuits, meals) have been shown to significantly increase urinary iodine concentrations in children. 1
Practical Dietary Recommendations
To meet the WHO-recommended 150 µg/day for adults (250 µg/day in pregnancy), consume two portions of fish weekly plus dairy equivalent to two glasses of milk, one yogurt, and one cheese serving daily. 1, 4
Key Caveats
- Ultra-high temperature (UHT) processed milk contains 30% less iodine than conventional milk. 1
- Iodine requirements increase to 220-250 µg/day during pregnancy and 290 µg/day during lactation. 4, 2
- The tolerable upper limit is 600 µg/day (European) or 1,100 µg/day (US), with excess intake risking thyroid dysfunction. 4, 5
- Women consuming plant-based diets or avoiding dairy/fish may require iodine supplementation, as these dietary patterns significantly increase deficiency risk. 1, 6, 2