From the sea, a source of nutrients

Uses: Kelp has long been taken as an iodine supplement to treat goiter or thyroid disease. Newer claims tout its use in weight loss, hair loss prevention, ulcer and constipation treatment, and cancer prevention.

Dose: Kelp comes in capsule, liquid and powder form. Products vary in nutrient content, so follow manufacturer instructions for recommended doses.

Precautions: Kelp from contaminated waters can contain heavy metals (such as lead) and other toxic chemicals. Check labels for nutrition information; too much iodine -- 2,000 micrograms a day or more -- can overstimulate the thyroid, enlarging the gland and causing heart palpitations, nervousness, sweating and other symptoms. (The U.S. recommended daily intake for iodine is 150 micrograms.)

Research: For years, researchers have suggested that diets high in kelp may lower the risk of certain types of cancer. Evidence comes largely from animal and a human studies that suggest the plant inhibits breast and prostate cancers. Recently, researchers at UC Berkeley concluded from a series of animal and small-scale human studies that it might be kelp -- not soy -- that’s behind the low rates of estrogen-related cancers among Japanese women. But because few clinical trials have examined kelp’s usefulness, experts caution against turning to the plant before more is known about how -- and how well -- it works.

Dietary supplement makers are not required by the U.S. government to demonstrate that their products are safe or effective. Ask your healthcare provider for advice on selecting a brand.