Seaweed, particularly varieties such as kelp, nori, and wakame, is sometimes promoted for nail health due to its rich content of minerals and vitamins, especially iodine, calcium, magnesium, iron, and certain B vitamins. These nutrients are essential for healthy nail growth and strength. There is some scientific rationale for the use of seaweed to support the nails, as deficiencies in minerals like zinc and iron are known to cause brittle or malformed nails. Seaweed is also a source of proteins and antioxidants that may contribute to overall tissue health.

However, direct clinical studies specifically evaluating the effects of seaweed supplementation on human nail strength or growth are lacking. Most of the evidence is extrapolated from general nutrition data and the knowledge that adequate intake of minerals and vitamins is important for the maintenance of healthy nails.

In summary, while there is a plausible scientific basis—because seaweed is nutrient-dense and these nutrients are beneficial for nails—there is limited direct research demonstrating a unique benefit of seaweed for nail health beyond its role as a general source of nutrients. Thus, the evidence is rated a 2 out of 5, reflecting weak but plausible scientific support rather than strong clinical validation.