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Botanical illustration of Kombu
CulinarySourced entry

Kombu

Saccharina japonica

A brown seaweed central to Japanese cooking and the main source of iodine in Japan. Too much iodine can harm the thyroid.

Safety at a glance

Tap a box to read the safety notes below. “Nothing recorded” means our sources don't cover it, not that it's safe.

Kombu may interact with some medicines. If you take any medicine, read Interactions with medicines below and talk to your doctor or pharmacist before using it.

What is Kombu?

Plant family
Laminariaceae, the kelp family of brown seaweeds
Parts used
The dried fronds (blades)
Where it grows
The coasts of Japan, Korea and northern China
Genus
Saccharina
Species
japonica

Also called

Kelp

Regional names

Konbu

Older scientific names

Laminaria japonica

Traditionally used for

  • Food
  • Iodine source

Traditionally described as

  • Very rich in iodine

Natural compounds

Iodine

How it's prepared

Common ways Kombu is prepared or sold. This isn't advice on how to take it; see Safety below.

Safety

Interactions with medicines

  • Iodine can interact with antithyroid medicines such as methimazole.[2]Health agency

Who should avoid it

  • A woman with an enlarged thyroid developed an overactive thyroid after drinking a kelp tea for 4 weeks. People with thyroid disease should avoid iodine-containing herbal products.[3]Study

Toxicity testing

  • Too much iodine can cause goiter (an enlarged thyroid), thyroid inflammation and thyroid cancer. The safe upper limit for adults is 1,100 micrograms a day from all sources, and lower for children (200 micrograms at ages 1 to 3).[2]Health agency

What does the research say?

Traditional use

These are traditional uses, not proven treatments.

  • Kombu is a brown seaweed central to Japanese cooking, eaten in many forms. About 90% of Japan's kombu is harvested around Hokkaido and has been shipped across the country along the "Kombu Road" since the 1600s.[1]Study

  • Seaweed is generally rich in iodine, which the body needs to make thyroid hormones. Kelp is also sold as an iodine supplement.[2]Health agency

Research in people

  • Brown seaweed like kombu is the main source of iodine in Japan, where people eat more iodine than most other populations, about 400 micrograms a day on average. In a survey of 2,845 adults, iodine levels were highest in areas that eat a lot of kelp.[1]Study

In short

Too much can cause thyroid problems; avoid kelp products with thyroid disease.

Sources

  1. [1] Nationwide survey on iodine nutritional status and thyroid function in Japanese adults · DOI: 10.1507/endocrj.EJ25-0603Peer-reviewed study
  2. [2] Iodine: Fact Sheet for Consumers — National Institutes of Health, Office of Dietary SupplementsGovernment health agency
  3. [3] Iodine-induced thyrotoxicosis after ingestion of kelp-containing tea · DOI: 10.1111/j.1525-1497.2006.00416.xPeer-reviewed study

This information is educational and traditional in nature, and is not a substitute for professional medical advice. Unfamiliar word? See what these words mean.