Coastal and marine foods differ widely in iodine content, with seaweeds, especially brown kelp species, providing the highest concentrations by a large margin. The Office of Dietary Supplements National Institutes of Health highlights seaweed as a concentrated dietary source of iodine, and cautions that levels can be extremely variable depending on species and harvest location. This variability makes portion size and species identification important for estimating intake.
Major seafood contributors
Among finfish, whitefish such as cod and haddock generally rank higher in iodine than oily fish; data compiled by the U.S. Department of Agriculture FoodData Central indicate that many Atlantic cod samples contain substantially more iodine per serving than tuna or salmon. Shellfish including shrimp, oysters, and mussels typically provide moderate to high amounts and are important sources in many diets. Farmed versus wild status, post-harvest processing, and whether fish are fed iodine-enriched feed can all influence final iodine content.
Causes of variation and cultural context
Iodine in seafood reflects the iodine content of local seawater, the biology of the species, and human practices. Seaweeds concentrate iodine from seawater, so brown kelps accumulate particularly large amounts; the World Health Organization notes that environmental and species-level differences produce wide concentration ranges. Coastal communities and traditional diets in East Asia often rely on seaweeds and shellfish, which raises average iodine intake compared with inland regions where iodized salt is the more consistent source. Territorial fisheries management and aquaculture feed choices can therefore have public-health implications.
Iodine is essential for thyroid hormone production, so iodine deficiency leads to goiter, developmental delays, and impaired cognitive outcomes, while excess iodine can trigger thyroid dysfunction in susceptible people. The World Health Organization describes both deficiency and excess as public-health concerns, and the Office of Dietary Supplements National Institutes of Health provides guidance on recommended intakes and upper limits. For individuals and public-health programs, understanding which seafoods are richest in iodine—and the environmental and cultural reasons for that richness—helps balance benefits against risks and supports targeted nutrition advice in coastal and inland populations. When relying on seafood for iodine, choosing species knowingly and considering local food composition data is the best practice.