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Seaweed and Women’s Health

by Dr Jane Jamieson(more info)

listed in women's health, originally published in issue 287 - June 2023


Why Consider Seaweed for Women’s Health Concerns?

Seaweed, or sea vegetables as they are sometimes called, are a rich source of whole-food nutrition. If they are grown and harvested correctly in pollution-free waters they can be a welcome addition to anybody’s diet. [Cherry et al., 2019] They have a special place in women’s health and it is likely that they were a traditional source of nutrition which supported fertility around the world. Seaweed is used extensively in other island nations, such as Japan, Korea and the Philippines.

One of the components of seaweed which is crucial for women’s health is iodine. Many people are aware of the importance of iodine for thyroid health. The thyroid hormones T3 and T4 are aptly named for the number of iodine atoms they contain. T3 contains three iodine atoms and T4 contains four. Good thyroid health is important for fertility, so supporting thyroid function is one way in which seaweed supports women’s health. There are other reasons why iodine is important for women’s health too. Iodine is used as an antiseptic. [Sibbald, Leaper and Queen, 2010] It is also needed in the body to protect tissues such as breast tissue from infection such as from bacteria, viruses and fungi. The milk ducts which allow milk to flow from the breast to the baby are an external opening and can allow bacteria and viruses into the breast. Higher iodine levels have been shown to protect the breast from breast cancer [Cotas et al., 2021] and there is a link between certain viruses causing certain cancers, so iodine may be protecting the breast in this way.


Seaweed and Women’s Health

Alaria Devon 2023


Seaweed has many other benefits which contribute towards women’s health. Many of the challenges associated with women’s health problems such as dysmenorrhoea, endometriosis, PCOS, infertility, menopause and breast cancer can be related to imbalances in the hormones: oestrogen and progesterone. This balance is affected by the clearance of these hormones, especially oestrogen. Oestrogens are metabolised by the liver and conjugated to functional groups (amino acids, sulphur, methyl groups for example) which aid its elimination, then they are excreted through the bile to the stool and then eliminated from the body. The challenge to hormone balance comes when the oestrogens are not cleared thoroughly from the body which leads to oestrogen dominance. This dominance is partly due to the excess amounts of oestrogen and partly due to the fact that the oestrogens have changed their function and become more potent after they have been metabolised by the liver.

Oestrogen needs to be cleared from the body by binding to soluble fibre. In addition, the oestrogen clearance is also affected by the bacteria in the digestive system. Certain bacteria can uncouple or deconjugate oestrogen from the functional groups which then allows oestrogens to be more readily reabsorbed back into the bloodstream. The key interventions that support oestrogen clearance are sufficient soluble fibre to bind to oestrogen to enable its elimination and a healthy microbiome in the gut which will cause deconjugate of oestrogen.

Several studies show the beneficial effect of seaweed polysaccharides (soluble fibre) on the gut microbiome and not surprisingly there is a corresponding positive effect of seaweed on changes in hormone balance too. In particular seaweed (Fucus vesiculosus, bladderwrack) has been shown to reduce the oestrogenic hormones and boost progesterone levels, bringing reproductive hormones into better balance. [Skibola, 2004; Teas et al., 2009]  In a pilot study where a few women had abnormally short menstrual cycles 0.7-1.4g of seaweed was shown to normalise their menstrual cycle, in a dose dependant manner.[Skibola, 2004] [Teas et al., 2009] showed that oestrogen levels were altered in a favourable way by the addition of seaweed in post-menopausal women and it was thought likely, that this was due to beneficial changes to the gut microbiome.

Many seaweeds have been shown to reduce inflammation in the body through several mechanisms: by inhibiting reactive oxygen species, and by regulating inflammation through reducing proinflammatory NF-κB signalling and by interfering with T-helper cell polarisation. [Olsthoorn et al., 2021] Improving inflammatory status is a positive attribute in endometriosis.

Whole-food Seaweed Versus Seaweed Extracts

Seaweeds and microalgae contain the full range of nutrients needed to sustain the marine ecosystem and the macro and micro algae are classed as the primary producers within this ecosystem. The nutrient profile of seaweeds is very rich and includes protein, omega-3 fatty acids, unusual polysaccharides, soluble fibre, vitamins, minerals, antioxidants and other phytochemicals which allow seaweed to adapt to its harsh and changing environment.[Hentati et al., 2020]

Understandably, given the unique properties of some of the polysaccharides and antioxidants in seaweed, there is a growing interest in the use of seaweed as therapeutic agents. This brings a trend towards extracting elements of the seaweed as they may yield different pharmaceutical agents. [Cherry et al., 2019; Cotas et al., 2021] Whilst this is likely to yield some interesting new medications it is losing sight of the fact that intact and whole seaweeds offer a broad range of nutrition, likely to stimulate and satisfy the body in ways that extracts which have been processed and refined cannot. It is after all, the consumption of whole-food seaweed by people, such as the Japanese, that has led us to understand the health benefits of these interesting foodstuffs. [Cherry et al., 2019; Teas et al., 2013] We must be careful that we do not throw the proverbial baby out with the bathwater. 

How Would we Use Seaweed in a Nutrition Protocol?

How should seaweed be used therapeutically? What seaweeds should be considered and how should these seaweeds be used. Another pertinent question to address is are there any safety concerns. The safety issues around seaweed relate to its allergenic potential, contamination by heavy metals and its iodine concentration.

Allergies regarding seaweed could include an allergy to the seaweed itself which is rare, or allergies to shellfish or fish which are more common. There is the potential for seaweed to be cross-contaminated by fish or shellfish and there are no regulations in place to ensure that all seaweed producers can guarantee that their product is contaminant free. Companies such as Seagreens do test their batches for contamination, so this would be the safest product to consume. Nevertheless, anybody who develops any allergic symptoms should stop their seaweed consumption. In order to test to see if somebody was likely to have an allergy to the seaweed, it would be possible to make the dried seaweed into a paste with water and place it directly on the skin. Leave the seaweed on the skin for twenty four hours or more, with a dressing over it, to see if the skin reacts. This is not a common reaction, for example in the case of one pilot of 81 participants, one person developed a rash after consuming seaweed. [Sterling and Butler, 2021]

Contamination by heavy metals would be an issue when consuming seaweed that has been harvested in polluted water.[Cherry et al., 2019; Lomartive et al., 2021] Choosing a responsible seaweed producer who tests their product for heavy metal contamination would address this issue. Companies like Clearspring, Cytoplan, G&G vitamins, Seagreens and Wise Owl Health should be considered. [Circuncisão et al. 2018] calls for regulation to address this issue, so that the public are able to be confident in any seaweed they might be consuming. Seagreens’ Health Foundation particularly has contributed to the development of a Nutritious Food Seaweed production standard, which since 2016 has been certified by the UK Biodynamic Association. It is the first food standard to require transparency for consumers of a minimum nutritional profile and the overall composition of seaweed.

There are other concerns over the iodine levels in seaweed. Seaweeds tested for iodine levels show a range of iodine concentration from 0.004 to 2.66g/kg. [Hentati et al., 2020] Seaweed producers like Seagreens® and the companies which use Seagreens ingredients in their products like Cytoplan Viridian and G&G indicate the levels of iodine in their product, so picking a suitable seaweed product should be straightforward. Choose a seaweed with high levels of iodine for somebody who has low iodine levels and vice versa for somebody who wanted to minimise their iodine consumption. It is worth considering that more than 60% of women in the UK are deficient in iodine. [Combet et al., 2014] so the majority of people will need iodine.

The question of which seaweed to choose is not an exact science as there is not enough research on each individual seaweed for all health complaints. Research into seaweed is showing a wide profile of nutrition for all seaweeds, the brown seaweeds generally have a greater concentration and range of minerals and antioxidants and the red seaweeds have a higher proportion of polysaccharides. [Begum et al., 2021; Circuncisão et al. 2018] Consuming seaweeds known for their nutritional profile, to support general health, reduce oxidative stress, support the microbiome and improve hormonal balance is an effective strategy and Ascophyllum nodosum, and fucus vesiculosus amongst others, fall into this category. [Begum et al., 2021; Circuncisão et al. 2018]

The therapeutic dose often used in literature can range from 0.7-5g of seaweed. [Cherry et al., 2019; Skibola, 1014; Teas et al., 2013] [Cotas et al. 2021] indicate that in Asian countries a daily intake of 4-7g of seaweed is consumed by regular seaweed eaters. The breakdown of the type of seaweeds used is not discussed, however. Nori (Porphyra umbilicalis), one of the common seaweeds used in sushi in Japanese cuisine is one of the lower iodine containing seaweeds, so it may not be wise to translate 4-7g directly into Western diets using the high iodine content seaweeds that are readily available in the UK. 

Seaweed has been shown to function in a dose-dependant manner and therefore, using the higher doses for a period of time may be recommended, although [Cotas et al, 2021] urges us to be cautious as once the dose gets too high, seaweed consumption can cause problems for human health.  Given the fact that seaweed modifies the microbiome and supports detoxification, it makes sense to start gently with seaweed and build up to a therapeutic dose (4-5g). A therapeutic dose could be sustained for several weeks or 1-2 months and then the dose could be tapered down to a maintenance dose (1-2g a day).

Many researchers caution using high doses of seaweed (5 grams or more) for an extended period of time and small amounts of seaweed (1 gram) used every day may be of benefit by consistently filling nutritional deficits rather than large doses used more infrequently. The body appreciates a steady supply of good quality nutrition.

Do monitor the symptoms of your client to see what works best for them. Some people will do well on lower doses of seaweed as a therapeutic dose and others will need to sustain a higher therapeutic dose of more than 1g for longer periods of time. This is where clinical judgement is important, and testing iodine levels can also play a part.


Begum et al., 2021. Antioxidant and Signal-Modulating Effects of Brown Seaweed-Derived Compounds against Oxidative Stress-Associated Pathology, Oxidative Medicine and Cellular Longevity. 2021.

Cherry et al., 2019. Risks and benefits of consuming edible seaweeds, Nutrition Reviews, 77, 5, 307-329. 2019.

Circuncisão et al. 2018. Minerals from macroalgae origin: Health benefits and risks for consumers, Marine Drugs, 16, 11. 2018.

Cotas et al., 2021. Seaweeds' nutraceutical and biomedical potential in cancer therapy: A concise review, Journal of Cancer Metastasis and Treatment, 7. 2021.

Hentati et al., 2020. Bioactive polysaccharides from seaweeds, Molecules, 25, 14. 2020.

Lomartive et al., 2021. An overview to the health benefits of seaweeds consumption, Marine Drugs, 19, 6. 2021.

Olsthoorn et al., 2021. Brown seaweed food supplementation: Effects on allergy and inflammation and its consequences, Nutrients, 13, 8. 2021.

Sibbald, Leaper and Queen, 2010. Iodine Made Easy, Wounds International, 2, 2, s1-s6.

Skibola, 2004. The effect of Fucus vesiculosus, an edible brown seaweed, upon menstrual cycle length and hormonal status in three pre-menopausal women: A case report, BMC Complementary and Alternative Medicine, 4. 2004.

Sterling and Butler, 2021. The Attenuation of Dysmenorrhea and Menorrhagia by the Red Seaweed Kappaphycus alvarezii: A Pilot Study. 2021.

Teas et al., 2009. The consumption of seaweed as a protective factor in the etiology of breast cancer: Proof of principle, Journal of Applied Phycology, 25, 3, 771-779.2009.

Teas et al., 2013. Dietary seaweed modifies estrogen and phytoestrogen metabolism in healthy postmenopausal women, Journal of Nutrition, 139, 5, 935-944. 2013.



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About Dr Jane Jamieson

Dr Jane Jamieson PhD MSc BSc P Dip NT is Course Director of MSc Nutrition Science and Practice at the Northern College of Acupuncture (NCA) and a Nutritional Therapist based in Edinburgh. Dr Jamieson may be contacted via Enabling Health 25/2 Regent Street Edinburgh EH15 2AY

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