Kelps are large seaweeds (algae) belonging to the brown algae (Phaeophyceae) Because of its high concentration of iodine, brown kelp (Laminaria) has been used to treat goiter, an enlargement of the thyroid gland caused by a lack of iodine. Kelp extract helps promote longevity and general youthfulness overall. Sea kelp extract may be helpful in preventing cancer and osteoporosis. Some use it to promote liver health. Kelp extract may also be helpful in ensuring healthy blood clotting.