Spirulina is a type of blue-green algae widely available in health-food stores as a dietary supplement. With a mineral-rich content, spirulina is high in calcium, iron, magnesium, potassium and zinc.It contains varying levels of iodine also.Some manufacturers market spirulina for thyroid support due to its iodine content. If you're considering taking spirulina specifically to benefit from its iodine content, there are some safety concerns for you to consider.ome manufacturers market spirulina for thyroid support due to its iodine content. If you're considering taking spirulina specifically to benefit from its iodine content, there are some safety concerns for you to consider.