Dr. Thomas Dwan - Is It Bad For You? Approved by Dr. Thomas Dwan

Is Seaweed Bad For You?



Short answer

Seaweed isn’t bad for you unless you have a thyroid condition.



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Long answer

There's a lot to recommend about seaweed. It's low in calories. It's got peptides that can improve the health of your heart. Seaweed comes with a whole mess of important vitamins. It's fibrous and can improve the health of your gut. Many seaweed products are lightly processed. According to the Guardian, there's also some evidence that it has antioxidant properties and can mop up certain chemicals in the body.

Is there such a thing as too much seaweed? Maybe. Seaweed is rich in iodine. Really rich in iodine - some varieties can pack multiple times your recommended daily intake in a single serving. Iodine in moderation is good: you need it to keep your thyroid functioning. Too much iodine, however, and you may aggravate your thyroid - especially if you have an underlying condition.

Talk to your doctor if you think the amount of seaweed you eat is interfering with your thyroid. Unless you've got a pre-existing condition or are eating large amounts of Kombu seaweed - one of the varieties with the most iodine - you should be alright. Boiling seaweed in soup helps to reduce the bioavailability of iodine content. Ditto if you prepare the seaweed with vegetables that are goitrogenic - that is, vegetables that interfere with the absorption of iodine. Certain kinds of seaweed are also goitrogenic themselves, which helps to soften the blow of their high iodine content.

Another concern about seaweed is that it sucks up some of the worst of the ocean - heavy metals and radiation - and then delivers it to our bodies. There's not much evidence to support that claim, though. One study conducted in Egypt looked at heavy metal accumulation in a range of seaweeds. It found that levels of heavy metals and other bioaccumulative toxins were well within the safety limits set by the World Health Organization and the governments of those countries in which the seaweed was harvested or consumed.

Concerns about radiation in seaweed are similarly overblown. Kelp Watch took samples up and down the Pacific after the meltdown at Fukushima - from Alaska to California to Hawaii. They found no detectable levels of radioactive isotopes in kelp or seaweed tissue. Other studies found minuscule levels of radioactive isotopes from Fukushima. Emphasis on minuscule - when looking for the isotope 134, they found amounts that were thousands of times less than the radiation you're exposed to during a standard x-ray. So while there are detectable levels of radiation in the Pacific, it's nowhere near the levels needed to be dangerous; it's less than the background radiation you're exposed to when you step outside. And it's not messing up your seaweed.

Possible short-term side effects

  • aggravate existing thyroid conditions


  • great source of protein
  • great source of vitamin c
  • high mineral content
  • one of the richest plant sources of calcium
  • natural source of iodine, which promotes thyroid health
  • anti-viral, anti-bacterial, anti-inflammatory properties

Our Wellness Pick (what is this?)

GimMe Seaweed Sheets

  • Rich in iodine
  • Source of Omega 3’s
  • Keto-friendly snack
  • Vegan & Gluten Free
  • Convenient & Healthy
Learn More!

Thank you for your feedback!

View Sources | Written by Sean McNulty
Published on: 11-23-2016
Last updated: 12-01-2023

Thank you for your feedback!

View Sources
Written by Sean McNulty
Published on: 11-23-2016
Last updated: 12-01-2023

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