Spirulina is a type of blue-green algae available as a dietary supplement in powdered, capsule or tablet form. According to MedlinePlus, spirulina is marketed as an alternative treatment for cardiovascular, digestive and immune system problems, but none of these claims are supported by scientific evidence.Like other sea vegetables such as seaweed, spirulina has a high concentration of iodine.ccording to MedlinePlus, spirulina is marketed as an alternative treatment for cardiovascular, digestive and immune system problems, but none of these claims are supported by scientific evidence. Like other sea vegetables such as seaweed, spirulina has a high concentration of iodine.