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Seaweed Nutrition

The only plants we can rely on as a source of iodine

The only plants we can rely on as a source of iodine

Last Updated: October 14, 2026 | ESPAÑOL

Seaweed is the only plant that we can rely on as an iodine source. While iodine may be present in other produce grown near the ocean, it is definitely there when the produce grows inside the ocean. And iodine is very important for us. We need it to produce thyroid hormone, key in regulating our body’s energy. Our little ones also need it for their skeletal and central nervous system development before and right after birth.

A lot of people also eat seaweed to get their vitamin B12. Yes, while we often hear that plants cannot provide this nutrient, seaweed may be the exception. The problem is that most seaweed contains B12 analogues (impostors) that attach to our B12 receptors preventing us from absorbing the real B12 from other sources. And even when it does contain actual B12, amounts vary immensely, making it risky to rely on this food as our primary source.

Other essential nutrients present in seaweed include vitamin A, vitamin B2 or riboflavin, vitamin B9 or folate, vitamin C, vitamin K, calcium, copper, iron, magnesium, and manganese. This means that seaweed is also good for our brain and nervous system, our heart, our immune system, our eyes, our red blood cells, our bones, our metabolism, our muscles, and our hair and skin.

Check out our personalized seaweed nutrition calculator below to see how much nutrition you and your family can get from eating seaweed.

Seaweed Nutrition Calculator

Important Things to Know

Hover over each of the interesting facts below to flip the tiles and learn more details.

Check out the interesting facts below! Tap on the red triangles to flip the tiles and learn more details.

Iodine

Iodine content varies immensely by type of seaweed.

Different types of seaweed provide dramatically different amounts of iodine. But iodine amounts within the same type of seaweed may also vary. A sheet of dry nori, for example, can provide anywhere from 35 to 55 mcg, while one teaspoon of dulse flakes gives us around 144 mcg, and just one and a half teaspoons of kelp can provide about 3855 mcg!

Eating kelp regularly could lead to hyperthyroidism.

Kelp is very high in iodine content. Just 1/8 tsp has approximately 965 mcg of iodine, that’s over six times the RDA and above the UL for anyone under 18 years old. Keep in mind that iodine content varies by region, so the content could be higher. For this reason, adults should not consume kelp regularly and children should avoid it completely.

Some seaweed contains B12, but most contain analogues.

Some seaweed and algae contain vitamin B12, however, most have B12 analogues that can actually block our B12 receptors promoting B12 deficiency. Those that do contain B12, like nori, vary in amounts tremendously, making it impossible to rely on it as a source.

This study found that 4 g (about 14 small sheets of nori) could provide 2.4 mcg a day. That’s a lot of nori every day! But again, even if we loved eating nori snacks or vegan sushi daily, there is no guarantee that this amount is the same in the nori we get at the store or even from one pack to the next.

Nori could help prevent breast and other hormonal cancers.

Seaweed like nori has strong anti-cancer properties, particularly against breast and other hormonal cancers. Evidence points at seaweed helping us metabolize our estrogen better, thus helping us get rid of any excess that could otherwise result in the growth of nasty hormonal cancer cells.

The benefits of spirulina might not be worth the risk.

Despite the hype that links spirulina to multiple health benefits, there is an important concern regarding cyanobacteria contamination.

Cyanobacteria produce cyanotoxins, including BMAA which is linked to the development of dreadful neurological disorders like Amyotrophic Lateral Sclerosis or ALS, or mycrocystin, a toxin that affects the liver and is highly present in spirulina products.

Microplastics have been found in commercial nori products.

A study in East Asia concluded that about 13% of total microplastic consumption in China came from eating seaweed, particularly kelp and nori.

The problem is not just microplastic contamination in the ocean. Seaweed like nori also gets its microplastics from plastic exposure during different processing stages.

Iodine

Iodine content varies immensely by type of seaweed.

Different types of seaweed provide dramatically different amounts of iodine. But iodine amounts within the same type of seaweed may also vary. A sheet of dry nori, for example, can provide anywhere from 35 to 55 mcg, while one teaspoon of dulse flakes gives us around 144 mcg, and just one and a half teaspoons of kelp can provide about 3855 mcg!

Eating kelp regularly could lead to hyperthyroidism.

Kelp is very high in iodine content. Just 1/8 tsp has approximately 965 mcg of iodine, that’s over six times the RDA and above the UL for anyone under 18 years old. Keep in mind that iodine content varies by region, so the content could be higher. For this reason, adults should not consume kelp regularly and children should avoid it completely.

Some seaweed contains B12, but most contain analogues.

Some seaweed and algae contain vitamin B12, however, most have B12 analogues that can actually block our B12 receptors promoting B12 deficiency. Those that do contain B12, like nori, vary in amounts tremendously, making it impossible to rely on it as a source.

This study found that 4 g (about 14 small sheets of nori) could provide 2.4 mcg a day. That’s a lot of nori every day! But again, even if we loved eating nori snacks or vegan sushi daily, there is no guarantee that this amount is the same in the nori we get at the store or even from one pack to the next.

Nori could help prevent breast and other hormonal cancers.

Seaweed like nori has strong anti-cancer properties, particularly against breast and other hormonal cancers. Evidence points at seaweed helping us metabolize our estrogen better, thus helping us get rid of any excess that could otherwise result in the growth of nasty hormonal cancer cells.

The benefits of spirulina might not be worth the risk.

Despite the hype that links spirulina to multiple health benefits, there is an important concern regarding cyanobacteria contamination.

Cyanobacteria produce cyanotoxins, including BMAA which is linked to the development of dreadful neurological disorders like Amyotrophic Lateral Sclerosis or ALS, or mycrocystin, a toxin that affects the liver and is highly present in spirulina products.

Microplastics have been found in commercial nori products.

A study in East Asia concluded that about 13% of total microplastic consumption in China came from eating seaweed, particularly kelp and nori.

The problem is not just microplastic contamination in the ocean. Seaweed like nori also gets its microplastics from plastic exposure during different processing stages.

References