Kelp (Iodine)
Also known as: kelp powder, Laminaria, Ascophyllum nodosum, sea kelp, bladderwrack iodine, iodine from kelp
Brown seaweed, usually Laminaria or Ascophyllum species, used as a whole-food iodine source in thyroid and multimineral formulas. Iodine content varies enormously between species, harvests, and processing, and surveys of commercial kelp products have found label-to-actual discrepancies and some products delivering well above the UL per serving. Standardized kelp extracts fix the iodine level, and heavy-metal testing for arsenic, cadmium, and lead is expected for any seaweed ingredient.
Research summary
Supplies iodine, largely as iodide, for thyroid hormone synthesis, along with seaweed polysaccharides and trace minerals.
Dosage
Daily amounts, elemental (1% of the compound is the element).
| Lowest studied | Typical range | Highest studied | Upper limit |
|---|---|---|---|
| 75 mcg | 150–300 mcg | 1,100 mcg | 1,100 mcg |
NIH ODS — UL of 1,100 mcg/day for adults from all sources
Doses are micrograms of iodine, not milligrams of kelp. The elemental fraction assumes a kelp extract standardized to 1% iodine (10,000 mcg/g), and raw_material_mg_per_dose_unit = 0.1 mg per mcg matches that; unstandardized kelp powders run anywhere from about 0.05% to over 0.5% iodine, so the fraction must be replaced with the supplier's assay value. Aakre 2021 documented wide variability and products exceeding the 1,100 mcg UL per serving. Keep general products near the 150 mcg RDA.
Standardization: standardized to 1% iodine (varies by supplier; set to certificate of analysis)
Source material: dried brown seaweed (Laminaria digitata, Ascophyllum nodosum) or standardized kelp extract
As supplied: Standardized extracts commonly 0.1–1% iodine; raw kelp is highly variable
Forms of Iodine
| Form | Typical dose | Element % | Formats | Price |
|---|---|---|---|---|
| Kelp (Iodine) | 150–300 mcg | 1% | Capsule, Powder, Tablet | low |
| Potassium Iodide | 150–300 mcg | 77% | Capsule, Powder, Tablet, Gummy, Liquid | low |
Format suitability
- Capsule
- Powder
- Tablet
- Softgel
- Gummy
- Liquid
Marine, fishy aroma limits use in gummies and liquids. Because iodine per gram varies, only standardized extracts should be used in metered formulas. Require heavy-metal (As, Cd, Pb, Hg) certificates for each lot.
Formulation notes
Iodine interacts with antithyroid drugs, lithium, and ACE inhibitors, and excess intake can disturb thyroid function in people with autoimmune thyroid disease; keep doses near the RDA in general products. Selenium is a common pairing in thyroid formulas. Count iodine from kelp, other seaweeds, and iodized-salt ingredients toward the total. Seaweed can carry inorganic arsenic; sourcing and testing are part of the formulation decision.
- Has an upper limit
- Notable drug interactions
- Possible Prop 65 warning
Sources
Related ingredients
Iron Bisglycinate
MineralFerrous iron chelated with two glycine molecules, the form most prenatal and gentle-iron products now use.
Typical: 18–30 mg
Vitamin B6 (Pyridoxine HCl)
VitaminPyridoxine hydrochloride is the standard, inexpensive, and highly stable form of vitamin B6 used in nearly all multivitamins and B-complex products.
Typical: 1.7–50 mg
Iron (Ferrous Sulfate)
MineralThe reference iron salt used in most clinical research and public-health programs, inexpensive and reliably absorbed.
Typical: 18–45 mg
Potassium Iodide
MineralThe standard iodine source in multivitamins, prenatals, and thyroid-support formulas, about 76.5% iodine by weight and absorbed almost completely.
Typical: 150–300 mcg
Iron (Ferrous Fumarate)
MineralA ferrous salt of fumaric acid that carries about 33% elemental iron, the highest of the common iron forms, which keeps tablets small.
Typical: 18–45 mg