Bladderwrack is a type of brown algae (seaweed) that grows on the northern Atlantic and Pacific coasts of the United States and on the northern Atlantic coast and Baltic coast of Europe. The main stem of bladderwrack, known as the thallus, is used medicinally. The thallus has tough, air-filled pods or bladders to help the algae float—thus the name bladderwrack. Although bladderwrack is sometimes called kelp, that name is not specific to this species and should be avoided.
Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.
For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
3 StarsReliable and relatively consistent scientific data showing a substantial health benefit.
2 StarsContradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1 StarFor an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.
This supplement has been used in connection with the following health conditions:
Refer to label instructions
Alginic acid, one of the major constituents in bladderwrack, is a type of dietary fiber that may be used to relieve constipation.
The laxatives most frequently used world-wide come from plants. Herbal laxatives are either bulk-forming or stimulating.
Basil (Ocimum basilicum) seed has been found to relieve constipation by acting as a bulk-forming laxative in one preliminary study.4 A similar study showed the seeds to be useful following major surgery for elderly people with constipation.5Alginic acid, one of the major constituents in bladderwrack(Fucus vesiculosus), is a type of dietary fiber that may be used to relieve constipation. However, human studies have not been conducted on the effectiveness of bladderwrack for this condition.
Refer to label instructions
Alginic acid, a constituent in bladderwrack, is a type of dietary fiber and as a result may help relieve diarrhea.
While fiber from dietary or herbal sources is often useful for constipation, it may also play a role in alleviating diarrhea. For example, 9–30 grams per day of psyllium seed (an excellent source of fiber) makes stool more solid and can help resolve symptoms of non-infectious diarrhea.6 Alginic acid, one of the major constituents in bladderwrack(Fucus vesiculosus), is a type of dietary fiber and as a result may potentially help relieve diarrhea. However, human studies have not been done on how effective bladderwrack is for this condition.
Refer to label instructions
Bladderwrack is high in mucilage, which may be advantageous for people with gastritis because its slippery nature soothes irritated mucus membranes of the digestive tract.
Demulcent herbs, such as marshmallow, slippery elm, and bladderwrack, are high in mucilage. Mucilage might be advantageous for people with gastritis because its slippery nature soothes irritated mucus membranes of the digestive tract. Marshmallow is used for mild inflammation of the gastric mucosa.7
Gastroesophageal Reflux Disease
Refer to label instructions
Bladderwrack is a soothing herb traditionally used to treat reflux and heartburn.
Other herbs traditionally used to treat reflux and heartburn include digestive demulcents (soothing agents) such as aloe vera, slippery elm, bladderwrack, and marshmallow.8 None of these have been scientifically evaluated for effectiveness in GERD. However, a drug known as Gaviscon, containing magnesium carbonate (as an antacid) and alginic acid derived from bladderwrack, has been shown helpful for heartburn in a double-blind trial.9 It is not clear whether whole bladderwrack would be as useful as its alginic acid component.
Refer to label instructions
Bladderwrack is a type of brown seaweed that contains iodine. Hypothyroidism due to insufficient iodine intake may improve with bladderwrack supplementation.
Bladderwrack (Fucus vesiculosus) is a type of brown seaweed that contains variable amounts of iodine.10 Hypothyroidism due to insufficient intake of iodine may possibly improve with bladderwrack supplementation, though human studies have not confirmed this.
Indigestion, Heartburn, and Low Stomach Acidity
Refer to label instructions
Bladderwrack is a demulcent herb, meaning it seems to work by decreasing inflammation and forming a barrier against irritants such as stomach acid.
Demulcents herbs may be used to treat indigestion and heartburn. These herbs seem to work by decreasing inflammation and forming a physical barrier against stomach acid or other abdominal irritants. Examples of demulcent herbs include ginger, licorice, and slippery elm.
The mucilage content in slippery elm appears to act as a barrier against the damaging effects of acid on the esophagus in people with heartburn. It may also have an anti-inflammatory effect locally in the stomach and intestines. Two or more tablets or capsules (typically 400–500 mg each) may be taken three to four times per day. Alternatively, a tea is made by boiling 1/2–2 grams of the bark in 200 ml of water for 10 to 15 minutes, which is then cooled before drinking; three to four cups a day can be used. Tincture (5 ml three times per day) may also be taken but is believed to be less helpful. Marshmallow and bladderwrack may be used the same way as slippery elm.
Refer to label instructions
Alginic acid is one of the main constituents in bladderwrack. Calcium alginate has shown promise as an agent to speed wound healing.
Alginic acid is one of the main constituents in bladderwrack (Fucus vesiculosus), a type of brown algae (seaweed). Calcium alginate has shown promise as an agent to speed wound healing in animal studies11 but has not been demonstrated to be effective in humans.
Traditional Use (May Not Be Supported by Scientific Studies)
Bladderwrack’s mucilaginous thallus has long been used to soothe irritated and inflamed tissues in the body.1 It was also historically used as a bulk-forming laxative.2 People living near oceans or seas have a historically low rate of hypothyroidism, due, in part, to ingestion of iodine-rich food, such as seafood and seaweeds like bladderwrack. It has also been used to counter obesity, possibly due to its reputation for stimulating the thyroid gland. Clinical research in this area has failed to confirm that seaweeds like bladderwrack help with weight loss,3 though more specific research is warranted.
How It Works
How It Works
There are three major active constituents in bladderwrack: iodine, alginic acid, and fucoidan.
The amount of iodine in bladderwrack is highly variable,12 probably as a result of different amounts of iodine in the water where it grows. A reasonable portion of bladderwrack may contain the U.S. adult recommended dietary allowance (RDA) of iodine (150 mcg). The RDA amount of iodine is believed to be necessary for maintenance of normal thyroid function in adults (infants and children need proportionally less). Thus, in people with insufficient iodine in their diet, bladderwrack may serve as a supplemental source of iodine. Either hypothyroidism or goiter due to insufficient intake of iodine may possibly improve with bladderwrack supplementation, though human studies have not confirmed this.
Alginic acid is a type of dietary fiber that can be used to help relieve constipation and diarrhea. However, human studies have not been done on how effective bladderwrack is for either of these conditions. An over-the-counter antacid, Gaviscon®, containing magnesium carbonate and sodium alginate (the sodium salt of alginic acid), has been shown to effectively relieve the symptoms of heartburn compared to other antacids in a double-blind study.13 However, bladderwrack has not been studied for use in people with heartburn. Bladderwrack might also help indigestion, though again clinical trials have not been conducted. Calcium alginate (the calcium salt of alginic acid) has shown promise as an agent to speed wound healing in animal studies14 but has not been demonstrated to be effective in humans.
Alginic acid has also been shown to inhibit HIV in the test tube.15 However, this effect has not been studied in humans. Alginic acid may help lower LDL (“bad”) cholesterol levels, according to animal studies.16 No human trials have studied this effect of bladderwrack. It is widely used in food and pharmaceuticals as a thickener and gelling agent.17
Fucoidan is another type of dietary fiber in bladderwrack that contains numerous sulfur groups. According to test tube and animal studies, this appears to give fucoidan several properties, such as lowering LDL cholesterol levels,18 lowering blood glucose levels,19 anti-inflammatory activity,20 possible anticoagulant effects,21 and antibacterial22 and anti-HIV activity.23 Though it has not been definitively proven, fucoidan is thought to prevent bacteria and viruses from binding to human cells, a necessary step in starting an infection, as opposed to killing the microbes directly.24, 25 To date, no human clinical trials have been done with fucoidan or bladderwrack to support their use for any of these conditions.
How to Use It
For short-term use (a few days) to relieve constipation, powdered bladderwrack can be taken in the amount of 1 teaspoon three times per day along with at least 8 oz of water each time.26 For thyroid problems, gastritis, or heartburn, 5 to 10 grams of dried bladderwrack in capsules three times per day has been recommended. Alternately, bladderwrack may be eaten whole or made into a tea using 1 teaspoon per cup of hot water, allowing each cup to sit at least 10 minutes before drinking. Three cups per day of tea can be drunk. No more than 150 mcg iodine should be consumed from all sources, including bladderwrack, per day.27 However, most bladderwrack products do not give any indication of their iodine content. Therefore, anyone considering taking bladderwrack should first consult a physician trained in nutrition and herbal medicine.
Interactions with Supplements, Foods, & Other Compounds
At the time of writing, there were no well-known supplement or food interactions with this supplement.
Interactions with Medicines
As of the last update, we found no reported interactions between this supplement and medicines. It is possible that unknown interactions exist. If you take medication, always discuss the potential risks and benefits of adding a new supplement with your doctor or pharmacist.
The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.
Bladderwrack is generally safe, though there are three potential problems with its consumption: acne, thyroid dysfunction, and heavy-metal contamination. Iodine in any form—including from bladderwrack and other seaweeds—can cause or aggravate acne in some people.28 Excessive iodine ingestion can cause either hypothyroidism or hyperthyroidism and should be avoided.29, 30 Bladderwrack and other seaweeds that grow in heavy-metal-contaminated waters may contain high levels of these toxins (particularly arsenic and lead), leading to nerve damage,31 kidney damage,32 or other problems. Only bladderwrack known to have been harvested from clean water or labeled to indicate the absence of heavy metals or other contaminants should be consumed. The safety of using bladderwrack during pregnancy and breast-feeding is unknown. People who are allergic to iodine may need to avoid bladderwrack.
1. Newall CA, Anderson LA, Phillipson JD. Herbal Medicines: A Guide for Health-Care Professionals. London: Pharmaceutical Press, 1996:124–6.
2. Mills SY. Out of the Earth: The Essential Book of Herbal Medicine. Middlesex, UK: Viking Arkana, 1991:514–6.
3. Björvell H, Rössner S. Long-term effects of commonly available weight reducing programmes in Sweden. Int J Obes 1986;11:67–71.
4. Kocharatana P, et al. Clinical trial of maeng-lak seeds used as a bulk laxative. Maharaj Nakornratchasima Hosp Med Bull 1985;9:120–36.
5. Muangman V, Siripraiwan S, Ratanaolarn K, et al. A clinical trial of Ocimum canum Sims seeds as a bulk laxative in elderly post-operative patients. Ramathibodi Med J 1985;8:154–8.
6. Eherer AH, Porter J, Fordtran JS. Effect of psyllium, calcium polycarbophil, and wheat bran on secretory diarrhea induced by phenolphthalein. Gastroenterol 1993;104:1007–12.
7. Blumenthal M, Busse WR, Goldberg A, et al, eds. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Austin: American Botanical Council and Boston: Integrative Medicine Communications, 1998, 167.
8. Golan R. Optimal Wellness. New York: Ballantine Books, 1995, 373–4.
9. Chevrel B. A comparative crossover study on the treatment of heartburn and epigastric pain: Liquid Gaviscon and a magnesium-aluminum antacid gel. J Int Med Res 1980;8:300–3.
10. Norman JA, Pickford CJ, Sanders TW, et al. Human intake of arsenic and iodine from seaweed based food supplements and health foods available in the UK. Food Add Contam 1987;5:103–9.
11. Barnett SA, Varley SJ. The effects of calcium alginate on wound healing. Ann R Coll Surgeons Engl 1987;69:153–5.
12. Norman JA, Pickford CJ, Sanders TW, et al. Human intake of arsenic and iodine from seaweed based food supplements and health foods available in the UK. Food Addit Contam 1987;5:103–9.
13. Chevrel B. A comparative crossover study on the treatment of heartburn and epigastric pain: Liquid Gaviscon and a magnesium-aluminum antacid gel. J Int Med Res 1980;8:300–3.
14. Barnett SA, Varley SJ. The effects of calcium alginate on wound healing. Ann R Coll Surgeons Engl 1987;69:153–5.
15. Béress A, Wassermann O, Bruhn T, et al. A new procedure for the isolation of anti-HIV compounds (polysaccharides and polyphenols) from the marine alga Fucus vesiculosus. J Nat Prod 1993;56:478–88.
16. Vázquez-Freire MJ, Lamela M, Calleja JM. Hypolipidaemic activity of a polysaccharide extract from Fucus vesiculosus L. Phytother Res 1996;10:647–50.
17. Lahaye M, Kaeffer B. Seaweed dietary fibres: Structure, physico-chemical and biological properties relevant to intestinal physiology. Sci Aliments 1997;17:564–84 [review].
18. Vázquez-Freire MJ, Lamela M, Calleja JM. Hypolipidaemic activity of a polysaccharide extract from Fucus vesiculosus L. Phytother Res 1996;10:647–50.
19. Vázquez-Freire MJ, Lamela M, Calleja JM. A preliminary study of hypoglycaemic activity of several polysaccharide extracts from brown algae: Fucus vesiculosus, Saccorhiza polyschides and Laminaria ochroleuca. Phytother Res 1996;10(suppl):S184–5.
20. Bartlett MR, Warren HS, Cowden WB, Parish DR. Effects of the anti-inflammatory compounds castanospermine, mannose-6-phosphate and fucoidan on allograft rejection and elicited peritoneal exudates. Immunol Cell Biol 1994;72:367–74.
21. Church FC, Mead JB, Treanor RE, Whinna HC. Antithrombin activity of fucoidan. The interaction of fucoidan with heparin cofactor II, antithrombin III and thrombin. J Biol Chem 1989;264:3618–23.
22. Criado MT, Ferreirós CM. Toxicity of an algal mucopolysaacharide for Escherichia coli and Neisseria meningitidis strains. Rev Esp Fisiol 1984;40:227–30.
23. Moen LK, Clark GF. A novel reverse transcriptase inhibitor from Fucus vesiculosus. Int Conf AIDS 1993;9(1):145, abstr. #PO-A03–0061.
24. Criado MT, Ferreirós CM. Toxicity of an algal mucopolysaacharide for Escherichia coli and Neisseria meningitidis strains. Rev Esp Fisiol 1984;40:227–30.
25. Lederman S, Gulick R, Chess L. Dextran sulfate and heparin interact with CD4 molecules to inhibit the binding of coat protein (gp120) of HIV. J Immunol 1989;143:1149–54.
26. Mills SY. Out of the Earth: The Essential Book of Herbal Medicine. Middlesex, UK: Viking Arkana, 1991:514–6.
27. Blumenthal M, Busse WR, Goldberg A, et al. (eds). The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Austin: American Botanical Council and Boston: Integrative Medicine Communications, 1998:315.
28. Harrell BL, Rudolph AH. Kelp diet: A cause of acneiform eruption. Arch Dermatol 1976;112:560 [letter].
29. Okamura K, Inoue K, Omae T. A case of Hashimoto’s thyroiditis with thyroid immunological abnormality manifested after habitual ingestion of seaweed. Acta Endocrinol 1978;88:703–12.
30. Kim JY, Kim KR. Dietary iodine intake and urinary iodine excretion in patients with thyroid diseases. Yonsei Med J 41:22–8.
31. Walkiw O, Douglas DE. Health food supplements prepared from kelp--a source of elevated urinary arsenic. Can Med Assoc J 1974;111:1301–2 [letter].
32. Conz PA, La Greca G, Benedetti P, et al. Fucus vesiculosus: A nephrotoxic alga? Nephrol Dial Transplant 1998;13:526–7 [letter].
The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2014.
How this information was developed to help you make better health decisions.
Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.