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Botanical name(s):

True kelps belong to the genus laminaria, family Laminariaceae. Giant kelps belong to the genus macrocystis, family Lessoniaceae. Bladder kelps belong to the genus nereocystis, family Lessoniaceae.

Other name(s):


General description

Kelp is a common name for leafy algae or seaweed.

Kelp needs sunlight as an energy source. It also needs a hard surface (not sand) on which to grow. Kelp grows quickly. In fact, giant kelp is one of the world's fastest growing plants. It grows as much as 300 feet (100 meters) in a single year.

Kelp contains iodine. This provides the trace element for your thyroid hormone.

Medically valid uses

Kelp is a food staple. It’s also used to make a group of compounds called alginates. These include carrageenan. Alginates are used in the food industry to stabilize and improve the textures of foods. These include ice cream and chocolate milk. The thick, smooth feel of chocolate milk is made by adding alginates. They’re also used in toothpaste and cosmetics.

Kelp is also used as soil conditioners. It adds organic material to soil that doesn't have enough nutrients.

As a supplement, kelp is used as a natural source of iodine. But the average laminaria-based supplement might contain large amounts of iodine. This can cause decreased thyroid function (hypothyroidism) or increased thyroid function (hyperthyroidism). If you already have hyperthyroidism, it can make your condition worse. Some supplements may also contain arsenic. There isn’t enough information to know if kelp supplements are safe.

Unsubstantiated claims

There may be benefits that have not yet been proven through research.

Kelp may improve sensory receptors. It may also promote healthy nails and blood vessels, aid in digestion, and ease constipation. It may also reduce hair loss and help with diabetes and weight management. Kelp may treat gastrointestinal ulcers. It’s also claimed to reduce the risk of breast cancer.

Dosing format

Kelp comes in powder and capsule form. Follow the instructions on the package for the correct dose.

Talk with your healthcare provider before taking any types of supplements.

Side effects, toxicity, and interactions

Both hyperthyroidism and hypothyroidism have been linked to too much kelp intake. This is due to its high amount of iodine. Abnormal thyroid function has also been linked directly to too much use of kelp supplements.

Kelp may contain harmful metals. These include cadmium, lead, aluminum, and other heavy metals. This is more likely if you eat a lot of kelp from areas of contaminated ocean water.

Women who are pregnant or breastfeeding shouldn’t use kelp supplements.

If you’re being treated for thyroid issues, you shouldn’t take kelp. You also shouldn’t use it if you take certain heart medicines.

If you need an X-ray with a contrast media, talk to your healthcare provider. You may have to stop taking kelp one month before your X-ray. You may not be allowed to take it again until the contrast medium leaves your body.

Online Medical Reviewer: Bianca Garilli MD
Online Medical Reviewer: Chris Southard RN
Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Date Last Reviewed: 8/1/2023