Potassium Iodide vs. Kelp
Among 5,236 on-market iodine products with an identifiable primary form, 69.1% use Potassium Iodide (3,619 products) and 30.9% use Kelp (1,617).
| Potassium Iodide | Kelp | |
|---|---|---|
| Quality tier | Tier 1 | Tier 3 |
| Iodine by weight | 76.4% | — |
| Share of market | 69.1% | 30.9% |
| On-market products | 3,619 | 1,617 |
| Median declared dose | 150 elemental mcg middle half: 75–150 | 150 elemental mcg middle half: 75–150 |
| Most common brands | Nature's Way, New Chapter, DC | Douglas Laboratories, New Sun, NOW |
Doses are declared per serving in elemental mcg. “By weight” is the share of the ingredient that is the nutrient itself (e.g. elemental magnesium in a magnesium salt).
Why Potassium Iodide is tier 1
Bioavailability 63.7-83.5% vs only 23.7-29.5% for kombu (kelp) in an RCT/crossover -- far more completely and predictably absorbed. "Potassium Iodine" is treated as a labeling variant of this form (not standard chemical nomenclature).
Source: Liu X et al. 2025, Food Sci Nutr 13(9):e70818
Why Kelp is tier 3
Bioavailability only 23.7-29.5% vs 63.7-83.5% for potassium iodide.
Source: Liu X et al. 2025, Food Sci Nutr 13(9):e70818
Tiers summarize published comparative bioavailability or outcome evidence for each form (see methodology).
This page describes the market; it is not a recommendation to take either form. Talk to a clinician about what's right for you.