Kelp
Kelp is a tier 3 form of Iodine, used in 1,759 on-market products .
1,759
on-market products
tier 3
quality tier
n/a
elemental fraction
Basis: Not a defined chemical salt -- iodine content and speciation vary enormously by species/harvest/processing (in one analysis of kombu, 50.9-55.0% of total iodine was inorganic iodide; Liu 2025)
Why this tier: Bioavailability only 23.7-29.5% vs 63.7-83.5% for potassium iodide in a small parallel-group trial (n=18 completers).
Source: Liu X et al. 2025, Food Sci Nutr 13(9):e70818