Seaweed, Sea Moss & Kelp

Iodine is the main concern with seaweed products. The American Thyroid Association advises against iodine and kelp supplements containing more than 500 mcg of iodine daily, for children and adults, including during pregnancy and breastfeeding. [1]

Overview and identity

"Seaweed" covers many different algae eaten as food or sold as supplements. "Sea moss" is a market name, not a single species: for example GBIF accepts Chondrus crispus (Irish moss) and Kappaphycus alvarezii, both red algae, as distinct species. [2] We did not find a regulatory definition of "sea moss", so check the Latin name, the source and the iodine content on the product. Kelp and other brown seaweeds are different again.

Iodine and the thyroid

The American Thyroid Association says many iodine, potassium iodide and kelp supplements contain iodine in amounts up to several thousand times the daily Tolerable Upper Limits. It advises against ingesting iodine and kelp supplements with more than 500 mcg of iodine daily, and says there is no known thyroid benefit of routine daily iodine above the US RDA. [1] People with thyroid disease should ask their clinician before using seaweed products.

Iodine research

A 2019 review of excess iodine says high intakes are well tolerated by most healthy people, but in some people excess iodine may precipitate hyperthyroidism, hypothyroidism, goiter or thyroid autoimmunity; people with existing thyroid disease or past iodine deficiency may be more susceptible, sometimes at intakes only slightly above need; iodine-induced hyperthyroidism can be life-threatening in some people; and sources of excess include certain seaweeds and iodine-containing supplements. [3]

What the research shows

PubMed lists over 13,000 records for these terms (see Research), but they include laboratory, food-science and nutrition work on many different seaweeds. Proper evidence not found (in sources we could read) for human trials supporting claims about sea moss for thyroid support, gut health, immunity or skin, so we make none. A search of the medical literature for "sea moss" or "Irish moss" returned mostly marine biology and carrageenan chemistry, not human trials.

Safety

• Iodine: see above. [1]
• Contamination and quality vary by source; see Quality.
• Sea moss gels are foods and supplements; there are no standard dose instructions we can verify.