Amount of Evidence: High Potential Benefits: High Safety: High
TABLE OF CONTENTS
What is nori?
Nori refers to any type of seaweed from the Porphyra family. It has been shown to benefit the body in many ways. The main compounds responsible for the effects of nori are iodine, fucoxanthin, fucoidan, and phlorotannins. With only 45 mcg of iodine per gram of dry weight, nori contains significantly less iodine than other types of seaweed. This makes nori safer than the other types since it would be hard to eat too much. This article is about the main benefits of nori, its potential side effects, the best time to take it, and more.
Potential benefits
It is important to note that all of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.
Major benefits
Correcting an iodine deficiency – Nori contains on average 45 mcg of iodine per gram of dry weight. Iodine deficiency can be terrible for your health and overall quality of life. Fortunately, a severe deficiency is relatively rare. A mild deficiency is much more common and can cause hypothyroidism, which can lead to many problems mentioned later in the article. If you are experiencing symptoms of deficiency or know that your iodine levels are too low, correcting an iodine deficiency is the main benefit of nori.
Minor benefits
Lowered blood glucose – While there are no long-term studies on this effect, nori can reliably reduce the blood glucose and insulin spike following a meal. It has also been shown to improve insulin sensitivity.
Weight loss – Fucoxanthin in nori notably increases metabolic rate. This effect has been noted primarily in obese, premenopausal women but likely applies to other groups of people as well. It appears to be the case that the more overweight a person is, the more effective fucoxanthin tends to be for weight loss. Some estimates say fucoxanthin could increase metabolic rate by as much as 450 kcal/day. It is important to note that this effect is not acute and happens over a longer period. It typically takes 5-10 weeks to start noticing this benefit.
Reduced liver fat – While more research is needed to show how reliable this effect is, fucoxanthin in nori seems to significantly reduce liver fat.
Lowered blood pressure – This effect is caused indirectly. Nori by itself does not seem to influence blood pressure but the fact that it aids weight loss and fat loss means it can lower blood pressure in obese or overweight individuals.
Anti-cancer properties – One of the compounds found in nori, fucoidan, is sometimes used along with other therapies for slowing down the growth of cancer cells. It can likely reduce the risk of getting cancer as well. Fucoidan is very effective in this regard in microorganism and animal studies. In those studies, fucoidan was able to decrease apoptosis and suppress angiogenesis. While human studies are limited, some have shown that taking fucoidan along with chemotherapy has been shown to decrease fatigue and improve well-being. One caveat to this benefit is that nori contains lower amounts of fucoidan than is being used for anti-cancer properties. This effect almost definitely applies to nori but only to a small degree.
Improved skin quality – More studies are needed to confirm this effect but from what we know so far, nori does seem to slightly improve skin quality.
Inflammation – Iodine and fucoxanthin in nori have both been shown to lower CRP (C-reactive protein), one of the main biomarkers of inflammation. Therefore, seaweed has antiinflammatory properties even if you are not deficient in iodine.
Fibrocystic breast disease – Iodine in seaweed may improve the tenderness associated with fibrocystic breast tissue, especially for people with low levels of the mineral.
Improved immunity – Fucoidan in nori has the potential to increase both innate and specific immune responses. For example, it increases an immune response connected to vaccinations. While this effect has only been shown in the elderly, it likely applies to young people as well. Probably the main reason behind this effect is that fucoidan helps stem cells move from the bone marrow into the peripheral circulation. Fucoidan has also been shown to have mild antiviral properties.
Reduced inflammation – Fucoidan in nori has been shown to lower some markers of inflammation. However, this effect may not apply to humans since all the studies so far have been done in vitro (with microorganisms) or in rat studies.
Increased SIRT1 and SIRT6 – Fucoidan has been shown to increase sirtuin 1 and sirtuin 6 activity, which implies it may be beneficial for slowing down aging. However, the connection between the supplement and healthspan or lifespan has not yet been established. Nori may slightly increase lifespan but this effect is yet to be proven.
Protection from radioactive iodine – Radioactive iodine gets released in nuclear accidents. High doses of non-radioactive iodine from nori or other sources can block the uptake of radioactive iodine in the thyroid.
Lowered triglycerides – While the effect is not too significant, fucoxanthin in seaweed can lower circulating triglycerides.
Reduced symptoms of brain injury – Fucoidan in the seaweed has a positive effect on healing traumatic brain injury. Besides its anti-inflammatory properties, fucoidan has also been shown to reduce the degeneration of neurons and block white blood cells to enter brain tissue.
Unproven benefits
There is not enough evidence that nori notably affects these health metrics, or the science shows little to no efficacy in these areas.
Blood flow – Scientific studies have never shown a significant effect on blood flow.
DNA protection – Nori has not been shown in human studies to protect DNA from oxidative damage. However, some of the components in the seaweed do act as antioxidants and may have a small positive effect.
Brain health and cognition – The seaweed does not directly improve brain health and cognitive abilities.
Testosterone – Nori does not significantly affect DHT, free testosterone, or total testosterone levels.
Cholesterol – Nori has no direct effect on HDL or LDL cholesterol levels.
Well-being – Supplementation with nori doesn’t appear to increase subjective well-being. However, the seaweed could improve your well-being if you are deficient in iodine.
Strength and muscle growth – The seaweed does not help you increase strength or muscle mass faster. Reliable human studies have never shown this effect.
Asthma – Nori has not been shown to help with asthma to a significant degree.
Power output during exercise – Supplementing with the seaweed does not directly influence power output during aerobic or resistance training. It does not impact VO2 max or aerobic endurance either.
Kidney function – Nori does not significantly change kidney function biomarkers.
Sleep quality – The supplement does not directly improve sleep quality. It also does not seem to affect sleep duration.
Stress and anxiety – The supplement does not affect cortisol levels, at least not directly.
Possible side effects
Most of these side effects have to do with consuming too much iodine. Even though the other compounds, such as fucoxanthin, could cause problems as well, they do not seem to be nearly as problematic in high amounts.
These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.
Allergy – Some people are allergic to seaweed and should avoid it.
Diarrhea – Diarrhea caused by nori or other types of seaweed is not dangerous (assuming it doesn’t lead to severe dehydration) and usually only occurs if you consume high amounts at once.
Nausea – Just like diarrhea, this side effect is not dangerous but can be unpleasant.
Iodine toxicity – Nori contains on average 45 mcg of iodine per gram of dry weight, which is a very high amount. While iodine toxicity is rare, consuming high amounts of the mineral could lead to some health problems over time. For example, over 18,000 mcg/d can cause goiter. Extremely high doses (in grams) could also lead to abdominal pain, fever, nausea, vomiting, and coma. Fortunately, it is almost impossible to eat grams (millions of mcg) worth of iodine from seaweed. However, it’s best to avoid very high amounts of seaweed since they do not appear to be safe to take over a long period. Specifically, you want to stay below 1000 mcg of iodine per day.
Worsened Hashimoto’s disease – Doses of iodine as low as 200 mcg daily have been shown to worsen symptoms of Hashimoto’s thyroiditis and Grave’s disease, autoimmune conditions that involve the body attacking its thyroid gland. Seaweed may not be safe if you have one of these conditions.
Worsened thyroid health – Doses of iodine higher than 1000 mcg taken daily over a long period can negatively change blood markers of thyroid health. However, this may not be a concern since some cultures eat as much as 15000 mcg daily without any apparent side effects.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, the supplement companies can change their manufacturers at any time without announcing it to the FDA.
Who should not consume nori?
You should probably avoid nori and other types of seaweed if you:
already consume high amounts of iodine from other sources
experience a severe adverse reaction after eating nori or taking it as a supplement
suffer from Hashimoto’s thyroiditis (even low doses of iodine have been shown to worsen symptoms of Hashimoto’s disease)
suffer from Grave’s disease (the same said about Hashimoto’s also applies to Grave’s disease)
are on a tight food and supplement budget (since there are more cost-effective supplements on the market for most people)
Who will benefit the most?
You should consider adding the seaweed to your diet or taking it as a supplement if you:
experience symptoms of iodine deficiency, or you know you are deficient based on blood tests
avoid iodized salt and don’t get enough iodine from food
are overweight and wish to lose weight
suffer from fibrocystic breast disease
regularly swim in chlorinated swimming pools (since chlorine might interfere with iodine function)
get exposed to flame retardants, dyes, insecticides, furniture foam, gasoline, and the casings of electronics (since bromine in these things also interferes with iodine function)
get exposed to high levels of radiation with radioactive iodine
have a high budget for food and supplements (since nori will likely do more good than harm, assuming it doesn’t lead to too much iodine in the body)
Symptoms of iodine deficiency
Iodine deficiency is rare in developed countries because of iodized salt and other interventions. With that said, some groups of people are at risk of deficiency.
Counter-intuitively, a deficiency is more common among health-conscious people. That is because many individuals who care about their health tend to avoid iodized salt and eat high amounts of cruciferous vegetables.
The most common symptoms of deficiency include:
Fatigue
Brain fog
Joint pain and stiffness
Swelling in the joints
Stiff muscles and muscle pain
Poor memory
Puffy face
Puffiness under the eyes
High cholesterol
Bloating and constipation
Impaired digestion, especially when it comes to fatty foods
Mood swings and depression
Breast pain
Increased rate of infections
Goiter (an enlarged thyroid gland)
Problems with periods (absent, irregular, or unusually heavy periods)
All of these are connected to and caused by hypothyroidism.
A deficiency is especially concerning during pregnancy and the first few years of life, because it can cause permanent developmental effects. Even mild hypothyroidism in children can cause a lifelong decrease in IQ and other problems.
Keep in mind that these signs are just indications of a deficiency. If you experience some of them, it does not necessarily mean you need more iodine. On the other hand, some people may be deficient even though they are completely asymptomatic.
With that said, if you experience many or most of these symptoms, there is a high chance that you are not getting enough iodine. The more of these symptoms you have and the more severe they are, the more likely you are to have a deficiency.
How much nori should you consume?
Since nori is very rich in iodine, you need to determine how much iodine you should consume. Nori contains on average 45 mcg of iodine per gram of dry weight.
The RDA (recommended daily allowance) for iodine is 150 mcg/day for both men and women. Two exceptions are pregnant and breastfeeding women. The RDA for pregnant women is 220 mcg, and for breastfeeding women, it is 290 mcg/day.
Those numbers were based on how much iodine the thyroid gland uses each day and how much is lost in the urine. While the daily amount you should be getting depends on multiple factors, 150 mcg is a great estimate.
If you are not getting enough iodine from food, 100-150 mcg appears to be the best dose to take for most people. This amount should provide most of the benefits without meaningful side effects. Feel free to experiment with up to 1000 mcg to see if a higher dose makes you feel better.
Certain things may increase your need for iodine. For example, fluoride, chlorine, and bromine all have the potential to interfere with iodine function. Fluoride is mainly found in toothpaste and fluoridated water. Chlorine is mainly found in swimming pools and cleaning products. Bromine is found in flame retardants, dyes, insecticides, furniture foam, gasoline, and the casings of electronics. The more you get exposed to these things, the more iodine you likely need.
Also, compounds known as goitrogens can interfere with the uptake of iodine into the thyroid gland. These are found primarily in fruits and vegetables, most notably in cruciferous vegetables.
Unless you are pregnant, breastfeeding, or trying to correct a severe deficiency, taking more than 150 mcg daily should not be necessary. Also, the higher the dose you take, the higher the risk for side effects.
The upper limit for iodine is 1000 mcg. Do not take more than this amount if you don’t have a great reason to do so.
Keep in mind that boiling seaweed for 15-30 minutes significantly reduces its iodine content. It can remove as much as 99% of the iodine from seaweed.
Other iodine supplements
The forms of iodine supplements include:
Other types of seaweed – Seaweed supplements are overall a much better way to get enough iodine than taking the mineral in its isolated form. This is because seaweed contains other beneficial compounds, such as fucoxanthin and fucoidan. While the content of iodine and other compounds varies greatly from one type of seaweed to another, all types share similar benefits. You can either supplement with them or simply take them dry. Kelp supplements are by far the cheapest and also tend to contain significantly more iodine than the other forms.
Lugol’s iodine – This form, also known as aqueous iodine, is a mixture of molecular iodine and potassium iodide. It is purer than kelp supplements.
Iodoral – Iodoral is also a combination of molecular iodine and potassium iodide and its effects are almost identical to Lugol’s iodine.
Nascent iodine – While some people claim nascent iodine can release energy when consumed and provide high doses of the mineral without hurting the thyroid, there is no high-quality scientific evidence to support these claims. This form is likely just as effective as the other forms but not more effective.
Povidone-iodine – This form is used topically or as a nasal spray. You can absorb iodine through the skin so this form can improve your iodine status. Unfortunately, it is difficult to accurately estimate the dose so povidone is not the best for this purpose.
Potassium iodide – Potassium iodide is the most popular iodide salt. This form is just as effective as the other forms.
Sodium iodide – The effects of this form are virtually identical to those of potassium iodide.
Potassium iodate – This form is commonly added to iodized salt. There is not a big difference between iodate salts and iodide salts as far as the effects on the body.
Of all these forms, seaweed appears to be the best one to supplement with. Whether you take nori or other forms doesn’t make a huge difference.
Iodine content in seaweed varies greatly from one type to another. Here are some popular types of seaweed and how much of the mineral they contain per gram of dry weight: – Kelp (1500 mcg/g) – Arame (700 mcg/g) – Bladderwrack (500 mcg/g) – Hijiki (390 mcg/g) – Alaria esculenta (100 mcg/g) – Kelp Granules (67 mcg/g) – Wakame (60 mcg/g) – Nori (45 mcg/g) – Dulse (45 mcg/g)
Kelp is the cheapest and most popular seaweed to supplement with because of its high iodine content. Typically, the more iodine a seaweed contains per mcg, the less expensive the supplements are.
Best time to consume nori
While iodine is a water-soluble mineral, nori and other types of seaweed are better taken with food because of all the other compounds, such as fucoxanthin and fucoidan. Most of these are fat-soluble and you need to consume them along with some dietary fat to absorb them properly.
Whether you consume nori in the morning or the evening doesn’t matter. It does not interrupt your sleep in any way.
Where to buy nori
Amazon seems to be the best option for ordering dry nori or nori supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.
Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
You can eat the seaweed or take it as a supplement daily and do not need to cycle it. However, it is certainly not a problem if you don’t consume it daily. Not eating nori every once in a while could lead to better absorption, but no studies have proven this.
All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, to dose them correctly, you may need a highly accurate scale (preferably 0.001g). You can get one for as little as $20 from Amazon.
Yes. The seaweed doesn’t impact your sleep in any negative way in the short term.
The supplements rarely go bad, but they can lose potency over time. The same can be said about dry seaweed.
Keep the seaweed or nori supplements in a cold, dark, and dry place, and they will remain just as potent for many months or even years.
Yes. The main compound in the seaweed that could cause problems in high amounts is iodine.
While toxicity is rare, too much iodine in the system can cause some health problems, such as goiter. Extremely high doses (in grams) could also lead to abdominal pain, fever, nausea, vomiting, and coma. It is best to stay below 1000 mcg daily to prevent these side effects.
The most common reason people become deficient is that they don’t get enough iodine from their diet. However, other things, such as sulforaphane in cruciferous vegetables, fluoride in water, chlorine in swimming pools, bromine in flame retardants, and other things, may also lead to a deficiency since they increase your need for iodine.
As for iodine in the seaweed, most of the mineral gets flushed out of your system within 24 hours. A small amount stays in your thyroid gland for much longer.
Fucoxanthin, fucoidan, and many other compounds in nori stay in your system for around 3 days. The half-life of fucoxanthin is around 7 hours.
In the long-term, it typically takes around a month after you start taking the seaweed to start noticing the benefits.
Yes, nori and other types of seaweed are vegan-friendly.
Iodine in the seaweed is water-soluble but most other compounds, such as fucoxanthin and fucoidan, are fat-soluble. Therefore, it is better to consume seaweed with a dietary source of fat.
No, it does not. The seaweed does not interfere with fasting in any significant way. However, it is still better to take it with a meal to increase the absorption of many of the beneficial seaweed compounds.
References
Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We excluded from consideration studies that are either confounded or have a high conflict of interest.
