Bladderwrack (Kelp)
Commonly used for
Metabolic Health
Where to Buy
Our experts personally review each product we recommend for quality and cost effectiveness.
The cheapest product is usually low quality, but more expensive doesn’t always mean better.
The cheapest product is usually low quality, but more expensive doesn’t always mean better.
Wellness uses
Thyroid support
This is anecdotal, and there isn't strong clinical evidence that it works for everyone.
What is it? / Overview
Bladderwrack and kelp supply iodine, a required substrate for thyroid hormone -- but in iodine-sufficient populations extra iodine doesn't improve thyroid function and can trigger dysfunction, including case-reported hyperthyroidism that resolved after stopping. Kelp can also concentrate heavy metals such as arsenic.
How is it used? / Administration
Form: Bladderwrack (Fucus vesiculosus) or kelp (Laminaria) powder or extract -- iodine content is unpredictable and can be very high
Typical dose studied: No reliable dose -- iodine content varies enormously by product and is often unlabeled
Timing: Not established
Little upside for most people, and the iodine content can disrupt thyroid function -- avoid with any thyroid condition or thyroid medication.
How well does it work? / Evidence
? Emerging / limited evidence
Who should avoid it?
Avoid with: Hypothyroidism / Hashimoto's thyroiditis; Hyperthyroidism / Graves disease; Benign thyroid nodule; Goiter (thyroid enlargement); Breastfeeding
Interacts with: Levothyroxine and antithyroid drugs -- unpredictable iodine load can destabilize dosing; Amiodarone, iodine-containing contrast -- additive iodine load
Already taking it? Given the unpredictable iodine content and case reports of kelp-induced hyperthyroidism, this is worth flagging to a doctor rather than continuing without thyroid monitoring, especially with any preexisting thyroid condition.
Research & references
Farebrother J et al. (2019). Excess Iodine Intake: Sources, Assessment, and Effects on Thyroid Function. Annals of the New York Academy of Sciences. Gherbon A et al. (2019). Transient Hyperthyroidism Following the Ingestion of Complementary Medications Containing Kelp Seaweed: A Case Report. Medicine. Jonklaas J et al. (2014). Guidelines for the Treatment of Hypothyroidism. Thyroid (ATA Task Force).
Disclosure: Knozela is a participant in the Amazon Associates affiliate program. Some "Where to buy" links on this page are affiliate links -- if you make a purchase through them, Knozela may earn a commission at no additional cost to you.