Ascophyllum nodosum

Ascophyllum nodosum (also known as knotted wrack) is a species of brown seaweed that only grows in the northern Atlantic. It has been shown to benefit the body in many ways. The main compounds responsible for the effects of Ascophyllum nodosum are iodine, fucoxanthin, fucoidan, and phlorotannins. Ascophyllum nodosum is one of the richest natural sources of iodine with an average of 650 mcg per gram. 

Correcting an iodine deficiency – Ascophyllum nodosum contains on average 650 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.

Lowered blood glucose – While there are no long-term studies on this effect, Ascophyllum nodosum 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 Ascophyllum nodosum 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 Ascophyllum nodosum seems to significantly reduce liver fat.
Lowered blood pressure – This effect is caused indirectly. Ascophyllum nodosum 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 Ascophyllum nodosum, 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 Ascophyllum nodosum contains lower amounts of fucoidan than is being used for anti-cancer properties. This effect almost definitely applies to Ascophyllum nodosum but only to a small degree.
Improved skin quality – More studies are needed to confirm this effect but from what we know so far, Ascophyllum nodosum does seem to slightly improve skin quality.
Inflammation – Iodine and fucoxanthin in Ascophyllum nodosum 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 Ascophyllum nodosum 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 Ascophyllum nodosum 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. Ascophyllum nodosum 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 Ascophyllum nodosum or other sources can block the uptake of radioactive iodine in the thyroid.
Lowered triglycerides – While the effect is not too significant, fucoxanthin in brown 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.

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 Ascophyllum nodosum 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 – Ascophyllum nodosum contains on average 650 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.

You should probably avoid Ascophyllum nodosum and other types of seaweed if you:

already consume high amounts of iodine from other sources
experience a severe adverse reaction after eating Ascophyllum nodosum 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)

Typical Mineral Analysis
Ph 7.63%
Potassium K 8.235%
Phosphorus P 0.090%
Sulphur S 1.210%
Magnesium Mg 0.559%
Sodium Na 2.211%
Calcium Ca 7.753%
Copper Cu 19mg/kg
Iron Fe 3808mg/kg
Manganese Mn 119 mg/kg
Silicon Si 2.347 %

In addition to the above known mineral elements seaweeds also contain many other minerals including iodine, amino acids and vitamins.

ASCOPHYLLUM NODOSUM

The North Atlantic Kelp—A Mineral-Rich Seaweed for Thyroid, Skin, and Metabolic Health

BOTANICAL IDENTIFICATION

Scientific Name: Ascophyllum nodosum (L.) Le Jolis
Common Names: Knotted Wrack, Rockweed, Norwegian Kelp
Family: Fucaceae

Ascophyllum nodosum is a brown seaweed characterized by long, olive-green fronds that can reach 2 meters in length. The fronds are flat, with distinctive air bladders (vesicles) appearing at intervals along the stem, aiding buoyancy.

It grows along the intertidal zones of the North Atlantic Ocean, particularly in the coastal waters of Norway, Iceland, Canada, and the British Isles. It thrives in rocky, cold-water environments with high nutrient availability.

CULTURAL AND HISTORICAL USE

Traditionally harvested by coastal communities of Northern Europe and Atlantic Canada, Ascophyllum nodosum has been used as both food and medicine. It was a staple mineral source in maritime diets, often added to soups, breads, and animal feed.

Historically, kelp ash was used as a source of iodine to prevent goiter and support thyroid health. Farmers spread dried kelp on fields as a natural fertilizer rich in micronutrients.

In modern natural medicine, it is used as a dietary supplement for metabolism, skin health, and detoxification.

KEY BIOACTIVE COMPOUNDS AND BENEFITS

The synergy of iodine and fucoidans supports endocrine health while providing anti-aging and immune-boosting effects.

HOW IT WORKS IN THE BODY

Iodine plays a key role in synthesizing thyroid hormones (T3 and T4), regulating metabolism, energy levels, and growth.

Fucoidans exhibit anti-inflammatory and antiviral activities by modulating immune responses and inhibiting viral replication.

Alginates bind heavy metals and toxins in the digestive tract, aiding detoxification and digestive health.

Polyphenols protect skin from UV damage and improve elasticity, while omega-3 fatty acids contribute to heart and brain health.

DOSE GUIDELINES

PREPARATION AND USES

Traditionally, dried kelp was ground and added to bread, soups, or porridge as a nutritional enhancer.

Modern applications include dietary supplements, powdered smoothies, and extracts used in skincare and haircare products for their mineralizing and antioxidant properties.

Ascophyllum nodosum is also used in animal nutrition to improve coat health and immunity.

OPTIMAL CONTEXT FOR USE

Ideal for individuals with low iodine intake or mild thyroid imbalances.

Supports detoxification programs, weight management, and skin rejuvenation when combined with other antioxidant-rich foods.

Pairs well with chlorella or spirulina for a comprehensive mineral and chlorophyll boost.

SUSTAINABILITY AND ETHICAL HARVESTING

Ascophyllum nodosum is hand-harvested along rocky coastlines to prevent damage to marine ecosystems. Sustainable practices involve cutting only the upper fronds, leaving the holdfast and lower stem intact for regrowth.

Certified organic and wild-harvested kelp is now commonly available from Norway, Iceland, and Canada.

SAFETY AND CAUTIONS

Excessive iodine intake from overuse may lead to thyroid dysfunction (both hyper- and hypothyroidism).

Individuals with thyroid disorders or those taking levothyroxine should consult a healthcare provider before use.

May cause mild digestive discomfort in high doses due to its alginate content.

Not recommended for people with severe seafood allergies.

REFERENCES

Fitton, J.H. (2011). “Therapies from fucoidan; multifunctional marine polymers.” Marine Drugs.
MacArtain, P., et al. (2007). “Nutritional value of edible seaweeds.” Nutrition Reviews.
Holdt, S.L., & Kraan, S. (2011). Bioactive compounds in seaweed: Functional food applications.
Teas, J. (1983). “Effects of kelp on thyroid function.” American Journal of Clinical Nutrition.

FINAL NOTE

Ascophyllum nodosum is a mineral powerhouse from the cold Atlantic seas, offering comprehensive support for thyroid balance, detoxification, and skin vitality. Its traditional uses are validated by modern science, making it a valuable supplement for both internal health and topical care.