Laminaria

BotanicalSeaweedBest with a meal

What is it

Laminaria (kelp) is a genus of brown seaweed. Supplements use whole-leaf kelp powder or extracts, primarily as a source of iodine, along with potassium, sodium, fucoidan, and alginate.

Evidence for 2 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Iodine intake

Strong Evidence

Effective iodine source; dose control is critical.

Cholesterol / glycemic effects (modest)

Limited Evidence

Small studies of alginate/fucoidan; clinical relevance modest.

How it works

Laminaria's iodine supports thyroid hormone synthesis. Variable iodine content (sometimes very high) is a key issue. Fucoidan (a sulfated polysaccharide) shows immunomodulatory and antiviral activity preclinically. Alginate slows gastric emptying and binds bile acids, contributing to modest cholesterol effects. Most consumer kelp use is for iodine intake.

Dosage

Iodine RDA is 150 mcg/day for adults; UL is 1100 mcg/day. Kelp products vary wildly (50 mcg to >5000 mcg iodine per dose). Check label and ideally testing.

When and how to take it

Take with meals. Avoid large variable doses near thyroid medication.

2 commercial forms

Compare the main delivery options and what they’re best suited for.

Whole kelp powder

Widely sold; quality varies.

Variable iodine; bulk-fiber effects.

Standardized kelp extract

Preferred for predictable dosing.

Controlled iodine content.

Safety

Variable and often excessive iodine content is the main safety issue. Excess iodine can cause both hyperthyroidism (Jod-Basedow) and hypothyroidism, especially in Hashimoto patients. Heavy metal contamination (arsenic, lead) is documented in some kelp products.

Who should be cautious

Thyroid disease (especially Hashimoto's), pregnancy (manage iodine carefully), known kelp allergy. Choose USP-verified or tested products to limit heavy metals.

Interactions

Iodine interacts with thyroid medications (levothyroxine, methimazole, propylthiouracil). May affect lithium and amiodarone.

Food sources

Kombu (1 g dried)

Amount
~1500-2500 mcg iodine (very high)
%DV
—

Wakame (1 g dried)

Amount
~50-100 mcg iodine
%DV
—

Nori (1 sheet)

Amount
~15-25 mcg iodine
%DV
—

Frequently asked questions

Is kelp the same as iodine?⌄

Kelp is a major dietary source of iodine but content varies hugely. Iodide or kelp-standardized extracts provide predictable doses.

Can I take kelp with my thyroid medication?⌄

Discuss with your prescriber. Iodine can interact with thyroid drugs in both directions.

References

Laminaria on Wikidata — Wikidata link

Laminaria on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Laminaria (PubMed search) — PubMed link

Track Laminaria with Pilora

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.