Kelp is the densest natural iodine source. It corrects a shortfall in people avoiding iodised salt, dairy, and seafood, and offers nothing to those who already have enough. Effects on blood sugar, cholesterol, and blood pressure are small. Excess iodine disturbs thyroid function in both directions and can worsen autoimmune thyroid disease. Products are often mislabelled and sometimes carry arsenic. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Thyroid-stimulating hormone (TSH) | 0.5–2.0 mIU/L | Earliest and most sensitive signal of an iodine-driven thyroid shift |
| Free thyroxine (free T4) | 1.0–1.5 ng/dL | Confirms whether a thyroid-stimulating hormone change reflects real hormone loss |
| Free triiodothyronine (free T3) | 3.0–4.0 pg/mL | Reflects conversion to the active hormone, which iodine excess can suppress |
| Thyroid peroxidase antibodies | Undetectable, below 9 IU/mL | Identifies autoimmune thyroid disease, the group in whom kelp is contraindicated |
| Spot urinary iodine concentration | 100–199 µg/L | Direct measure of iodine status and of whether the dose is on target |
| Serum selenium | 120–150 µg/L | Determines whether the enzymes limiting iodine-driven oxidative injury are supported |
| Urinary total and speciated arsenic | Total below 35 µg/g creatinine; inorganic and methylated forms below 15 µg/g | Detects contamination from an uncertified product |
| Serum potassium | 4.0–4.5 mmol/L | Kelp adds potassium, which matters where kidney function is reduced |
| LDL cholesterol | Below 100 mg/dL, lower where cardiovascular risk is elevated | Tracks the lipid effect where cholesterol lowering is the intended target |
Cadence: Baseline before starting; thyroid-stimulating hormone and free thyroxine at six to eight weeks, again at six months, then annually while intake continues. Urinary iodine rechecked at three months; urinary arsenic added at six months where the product lacks third-party contaminant certification.