Kelp (Fucus vesiculosus, other Fucus species, and Ascophyllum nodosum), also known as bladderwrack, consists of the dried whole plant. It contains soluble fiber (e.g., alginic acid), vitamin B12, iron and iodine. It can also contain heavy metals (e.g., arsenic, cadmium, lead). Brown seaweed (Undaria pinnatifida) is a purported galactogogue in some Asian cultures; however, no scientifically valid clinical trials support this use. Galactogogues should never replace evaluation and counseling on modifiable factors that affect milk production.[1,2] No data exist on the excretion of any organic components of seaweed into breastmilk; however, iodine is actively transported into breastmilk and heavy metals are excreted into milk. For further information on iodine in breastmilk and its potential adverse effects, see the iodine record in LactMed. Some sources recommend against using seaweed during breastfeeding because of its high iodine content,[3-5] and potential contamination with heavy metals.
Dietary supplements do not require extensive pre-marketing approval from the U.S. Food and Drug Administration. Manufacturers are responsible to ensure the safety, but do not need to prove the safety and effectiveness of dietary supplements before they are marketed. Dietary supplements may contain multiple ingredients, and differences are often found between labeled and actual ingredients or their amounts. A manufacturer may contract with an independent organization to verify the quality of a product or its ingredients, but that does not certify the safety or effectiveness of a product. Because of the above issues, clinical testing results on one product may not be applicable to other products. More detailed information about dietary supplements is available elsewhere on the LactMed Web site.