IngredientsMarine macroalgae (also referred to as seaweeds) belong to three major classes or phyla: Chlorophyceae (green algae), Rhodophyceae (red algae), and Phaeophyceae (brown algae). Brown algae is comprised of 20 classes; the class Phaeophyceae alone accounts for over 1,800 species and 66% of the total algae consumption. The term "brown algae" thus refers not to a single botanical species but to an entire taxonomic class of marine macroalgae unified by their characteristic brown-to-olive pigmentation, derived from the xanthophyll pigment fucoxanthin, which masks their chlorophyll.
The most common species are the kelps Laminaria (kombu), Undaria (wakame), and Macrocystis. Other commercially and medicinally significant species include Fucus vesiculosus (bladderwrack), Ascophyllum nodosum (knotted wrack), Ecklonia cava, Sargassum spp., and Cladosiphon okamuranus (Okinawa mozuku).
Fucus vesiculosus is known by the common names black tang, bladder fucus, brown algae, brown seaweed, dyers fucus, red fucus, rock wrack, and rockweed. Fucus vesiculosus L., known as bladderwrack, belongs to the brown seaweeds, which are widely distributed throughout northern Russia, Atlantic shores of Europe, the Baltic Sea, Greenland, the Azores, the Canary Islands, and shores of the Pacific Ocean.
Sargassum, a genus of brown seaweed (Phaeophyceae) in the Sargassaceae family, contains approximately 400 species and is found throughout all oceans, consumed as food and medicine in many cultures.
Brown algae are available in a wide range of supplemental and food forms:
With the development of mass food manufacturing in the early 1900s, seaweed components were harnessed industrially. Hydrocolloids, such as alginate, carrageenan, and agar, are still the most commonly used components because of their gelling properties in foods, pharmaceutical and biotechnological applications.
Brown algae (Phaeophyceae) have been consumed by humans for hundreds of years. Since ancient times, seaweeds have been used as food products and as traditional medical agents, especially in Asian countries.
Sargassum spp., a brown seaweed, has been used in Traditional Chinese Medicine (TCM) for nearly 2,000 years to treat a variety of diseases including thyroid disease (e.g., goitre). Traditional Chinese medicine used hot water extracts of several types of seaweed in the treatment of cancer, and the Japanese and Chinese cultures used seaweed to treat goiter and other glandular problems as long ago as 300 BC.
The Chinese are perhaps the people in Asia who have the most extended use of selected seaweeds traditionally in their medications for human ailments. Amongst the most utilized brown seaweed species by Chinese are Sargassum fusiforme (Yang Xi Cai), Sargassum fulvellum, Sargassum thunbergii, and Sargassum horneri, among others.
Fucoidan has been used as an anticancer drug in traditional Chinese medicine. Traditional Chinese medicine also includes the brown alga Laminaria in the treatment of cancer, and there is even a mention in the Ebers Papyrus of the ancient Egyptians having used seaweed to treat breast cancer.
Some Western herbal products containing Fucus vesiculosus are known to be used topically for the treatment of sore knees, healing wounds, and also as herbal teas for their laxative or weight control effects. F. vesiculosus has been reported for the treatment of the uterus and ovaries in the Caribbean islands.
Well-known in Asian cuisine but also reported in the anthropologic literature from other prehistoric cultures, including Native American nations, seaweed has long been included in the human diet.
The anticarcinogenic properties of brown seaweeds (kelps, wracks, and others) are well known in some cultures but not yet scientifically understood. Traditional Chinese medicine includes the brown alga Laminaria in the treatment of cancer and it has also been recommended in ancient Ayurvedic texts.
Seaweeds have been used traditionally as food, folk remedies, dyes, and fertilizers. The uses were preparationally diverse β including internal decoctions and hot-water extracts for glandular conditions, topical poultices for skin complaints, and dietary incorporation as a mineral-rich food source.
Brown algae present sulfated polysaccharides (alginates, fucoidans, and laminarins), proteins, minerals, vitamins, dietary fibers, fatty acids, pigments, and bioactive compounds that can positively contribute to the development of highly nutritious food products.
Fucoidans are polysaccharides containing substantial percentages of L-fucose and sulfate ester groups, and are constituents of brown seaweed and some marine invertebrates. The polysaccharide was named "fucoidin" when it was first isolated from marine brown algae by Kylin in 1913; it is now named "fucoidan" according to IUPAC rules, but is also called fucan, fucosan, or sulfated fucan.
Fucoidans are a group of polysaccharides (fucans) primarily composed of sulphated L-fucose with less than 10% of other monosaccharides. They are widely found in the cell walls of brown seaweeds, but not in other algae or higher terrestrial plants. The major function of fucoidans in cell walls is mechanical support and protection against desiccation during air-exposure of the seaweed at low tide.
Fucoidan is primarily composed of sulfated L-fucose and different proportions of xylose, mannose, galactose, glucose, and uronic acid depending on the species of brown seaweeds. Its structure is heterogeneous. Two main types of fucoidan backbone have been identified as mono-(1β3)-Ξ±-L-fucopyranose and repeated alternating (1β3)- and (1β4)-Ξ±-L-fucopyranose with sulfate groups locating at C-2, C-3 and/or C-4 of the fucose ring. Fucoidan was first isolated from brown algae in 1913 by Kylin, and has since been marketed as a dietary supplement in the food industry; since its discovery, fucoidan has attracted steadily increased research interest, attributed to its low toxicity and diverse bioactivities.
Mechanisms of action: For the past decade, fucoidans isolated from different species have been extensively studied due to their varied biological activities, including anticoagulant and antithrombotic, antiviral, antitumor and immunomodulatory, anti-inflammatory, blood-lipid-reducing, antioxidant and anticomplementary properties, activity against hepatopathy, uropathy and renalpathy, gastric protective effects, and therapeutic potential in surgery.
Fucoidan, a sulfated polysaccharide purified from brown algae, has a variety of immune-modulation effects, such as promoting activation of dendritic cells (DCs), natural killer (NK) cells, and T cells, and enhancing anti-viral and anti-tumor responses. The anticoagulant activity of fucoidans from brown algae depends on their molecular weight, the degree of sulfation, and the distribution of sulfate groups in the repeating monosaccharide units.
Among the major polysaccharide components in brown algae are alginate, laminarin, and fucoidan. The polysaccharides alginate, laminarin, and fucoidan account for more than 50% of the total dry weight of brown algae, and can reach up to 70% in some species. Alginate is a linear acidic soluble dietary polysaccharide; when ingested, it forms a viscous gel in the gastrointestinal tract, contributing to its dietary fiber and satiety-promoting properties. Bioactivity has been demonstrated for alginate as a linear acidic soluble dietary polysaccharide.
The algal-derived fibre laminarin (LAM), a Ξ²(1β3, 1β6)-linked glucan, has shown immunomodulatory activity. Algal-derived polysaccharides have gained much interest owing to their abundance as the main cell wall constituent as well as their unique physicochemical and biological properties. Marine algal polysaccharides, including laminarin, fucoidan, ulvan, carrageenan, and alginate, have been widely explored for food, pharmaceutical, and biomedical applications. Laminarins showed greater Ξ±-glucosidase inhibitory effects compared to fucoidans.
Fucoxanthin is a characteristic carotenoid found in brown algae. Found primarily in brown algae (Phaeophyceae), this orange-brown pigment is what gives seaweeds their characteristic color. It is part of the carotenoid family, but with a unique twist: its molecular structure includes a rare allenic bond, which scientists believe contributes to its potent biological activity. Fucoxanthin is prevalent in brown seaweed because it functions as a light-harvesting complex for algal photosynthesis and photoprotection.
Recent studies have reported that fucoxanthin has many physiological functions and biological properties, such as antiobesity, antitumor, antidiabetes, antioxidant, anti-inflammatory, and hepatoprotective activities, as well as cardiovascular and cerebrovascular protective effects.
Among categories of phlorotannins, eckol derivatives are pharmacologically prominent. These polyphenolic compounds are characterized by a dibenzo-1,4-dioxin unit in the molecular skeleton, which is found only in some specific brown algae such as Eisenia and Ecklonia species. Phytosterols, including both sterols, stanols, and oxysterols, such as fucosterol, saringosterol, and 24-hydroperoxy-24-vinyl-cholesterol, are a group of functional lipid compounds. Compared to other bioactive molecules produced by brown algae, phytosterols exhibit various health-improving effects, especially neuroprotective and anti-inflammatory.
There are three major active constituents in bladderwrack: iodine, alginic acid, and fucoidan. The amount of iodine in bladderwrack is highly variable, 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).
Compared to terrestrial plants, brown algae have a higher proportion of essential fatty acids such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) fatty acids. In addition, there are several secondary metabolites that are synthesized by algae such as terpenoids, oxylipins, phlorotannins, volatile hydrocarbons, and products of mixed biogenetic origin.
Seaweeds contain various functional components, such as polyphenols and fucoidan, which have been reported to exert multiple benefits, including blood glucose regulation, improved intestinal health, and enhanced lipid profiles.
A comprehensive 2023 meta-analysis published in Nutrients represents the strongest pooled human evidence to date. The characteristics of the 23 included randomized controlled trials (RCTs) are outlined in the meta-analysis, with 23 papers ultimately included for analysis. The findings indicate that supplementation with algae did not yield a significant alteration in fasting blood insulin (FBI) levels; nevertheless, a noteworthy reduction in fasting blood glucose (FBG) levels was observed following seaweed consumption (mean difference β0.165, 95% CI [β0.325, β0.005], p = 0.043).
An earlier systematic review and meta-analysis also examined RCT data on brown seaweed and plasma glucose. Neither low nor high doses (0.5 g and 2 g) of polyphenolic-rich brown algae (Fucus vesiculosus) produced a significant effect on postprandial plasma glucose (PPG). A blend of brown seaweeds (10% polyphenols, 90% algal polysaccharides) at a 500 mg dose also showed no significant effect in terms of lowering PPG.
Regarding specific extracts, a study investigated the acute effects of brown algae extracts (Ascophyllum nodosum and Fucus vesiculosus) on postprandial glucose and insulin concentration, where participants were given 508 mg of brown algae extract 30 minutes prior to 110 g of carbohydrate consumption. Acute insulin concentration was significantly decreased (p < 0.05) in the brown algae group compared to placebo, while the postprandial glucose concentration decreased but did not reach statistical significance (p > 0.05).
Evidence summary: The aggregate evidence from human RCTs suggests a modest and statistically marginal benefit of brown seaweed consumption on fasting blood glucose, but results are inconsistent across individual studies, populations, and preparations. Effects on postprandial glucose and insulin are mixed. Most individual trial populations are small, study durations are short, and preparations are highly heterogeneous, limiting conclusions. This area remains active but the overall evidence is preliminary.
Fucoxanthin, a brown-seaweed-extracted carotenoid, has exhibited anti-obesity properties in some clinical trials through its ability to overexpress uncoupling protein (UCP1) in white adipose tissue, which leads to fat burning.
The most frequently cited human trial involved a combined supplement of brown seaweed extract and pomegranate seed oil. The effects of a product were investigated that contained brown marine algae fucoxanthin as well as pomegranate seed oil. Daily administration of 600 milligrams of an extract that contained 2.4 milligrams of fucoxanthin per day resulted in significant weight loss compared with placebo after 16 weeks. The authors reported increases in resting energy expenditure, decreases in body and liver fat content, and improvements in the plasma lipid profile. Weight reductions were about 5 kg (11 lbs) more in the supplemented group compared with the placebo group.
At the molecular level, animal-model treatments with fucoxanthin improved energy expenditure, Ξ²-oxidation, and adipogenesis by upregulating PPARΞ±, PGC1Ξ±, PPARΞ³, and UCP-1. A clinical trial of 60 Japanese adult men and women of normal and obese weight found that 2 mg/day of fucoxanthin intake markedly reduced HbA1c and glycated albumin levels in subjects possessing the UCP1β3826 A/G thrifty allele.
Evidence summary: Evidence for fucoxanthin and body weight in humans is very limited. Fucoxanthin has exhibited anti-obesity properties in some clinical trials, but since the clinical trials apply pure fucoxanthin instead of fucoxanthin-bearing dietary supplements, a critical analysis is warranted to quantify fucoxanthin in brown seaweeds to validate their rationale in weight loss mechanisms. The available human RCTs are few, often use combination products making attribution of effect difficult, and most mechanistic data come from animal models. The evidence is currently preliminary.
Fucoidans have been shown to exhibit a variety of beneficial pharmacological effects, including antitumor, anti-inflammatory, immunomodulatory, antioxidant, anticoagulant, antithrombotic, antiangiogenic, and antiviral activities.
In research comparing fucoidans obtained from Ascophyllum nodosum, Macrocystis pyrifera, Undaria pinnatifida, and Fucus vesiculosus for their effect on the apoptosis of human neutrophils, activation of mouse NK cells, maturation of spleen dendritic cells, proliferation and activation of T cells, and adjuvant effect in vivo, fucoidans from M. pyrifera and U. pinnatifida strongly delayed human neutrophil apoptosis at low concentration, whereas fucoidans from A. nodosum and F. vesiculosus delayed human neutrophil apoptosis at higher concentration.
The biological properties of fucoidan vary depending on the species of algae, molecular weight, composition, and structure. Fucoidan derived from Gagome kombu (Kjellmaniella crassifolia) has been confirmed to be safe in healthy volunteer subjects and has been reported to prevent immune function deterioration.
Evidence summary: Immunomodulatory effects of fucoidan are well-supported in preclinical (in vitro and animal) settings, with several mechanistic pathways identified. Human evidence is limited and primarily from small pilot trials; robust RCTs establishing clinical immunological benefit in humans are lacking.
Investigations on the crude extracts of Phaeophyceae or brown algae revealed marked antitumor activity, eliciting a variety of research to determine the active ingredients involved. The sulfated polysaccharide of fucoidan and carotenoid of fucoxanthin were found to be the most important active metabolites of brown algae as potential chemotherapeutic or chemopreventive agents.
Existing research has demonstrated that fucoidan can directly exert anti-cancer actions through cell cycle arrest, induction of apoptosis, etc., and can also indirectly kill cancer cells by activating natural killer cells, macrophages, etc. In vitro studies show that fucoidan has antitumor, antiangiogenic, antiviral, antiarthritic, and immunomodulatory effects. Fucoidan also exhibited neuroprotective, radioprotective, and antiulcer properties.
The antitumor effects of fucoidans have been extensively investigated in vitro in various tumor cell lines, especially in lung and breast cancer cell lines, and in vivo in animal models. The aqueous extract isolated from the sporophyll of Undaria pinnatifida (Mekabu) showed strong in vivo and in vitro antitumor activity against breast cancer cells, with significant antiproliferative activity against three kinds of human breast cancer cells β MCF-7, T-47D, and MDA-MB-231 β through induction of apoptosis.
Evidence summary: The anticancer evidence base for fucoidan and fucoxanthin is substantial in preclinical settings (cell lines and animal models), but fucoidan is a sulfated polysaccharide found in the cell walls of many species of brown seaweed, and in vitro studies show antitumor and antiangiogenic effects β meaning the direct applicability to human cancer therapy remains unestablished. Clinical trials in humans testing brown algae constituents as primary anticancer therapy are limited, and most published clinical oncology data have used fucoidan as an adjuvant. No brown algae preparation has regulatory approval as a cancer treatment.
Inhibitory activity against angiotensin-converting enzyme I (ACEI) has been reported for a Fucus spiralis extract; fucoidans are recognized for their cardiovascular and antihypertensive effects through ACE inhibition. Clinical studies evaluating antihypertensive activity of bladderwrack specifically are lacking. Consumption of seaweed is noted to be associated with a decreased risk for ischemic heart disease.
Numerous and increasing evidence has proven that fucoidan is promising for application in treating cardiovascular diseases. The anticoagulant activity of fucoidans from brown algae depends on their molecular weight, the degree of sulfation, and the distribution of sulfate groups in the repeating monosaccharide units.
Evidence summary: Cardiovascular and anticoagulant effects are supported by in vitro and some animal data. Observational associations between seaweed consumption and reduced cardiovascular risk exist in population studies, but high-quality human interventional trials confirming these benefits are limited.
The algal polysaccharides laminarin and fucoidan have potent anti-inflammatory activities in the gastrointestinal tract. Fucoidan exhibited antiulcer properties in vitro, and in animal models fucoidan exerts anti-inflammatory effects to protect against various organ injuries and improved inflammatory pathology of acute colitis.
As dietary fibers, alginates and laminarin contribute to prebiotic effects in the colon. Polysaccharides are the main constituents of brown algae; their diverse structures allow many unique physical and chemical properties that help to moderate a wide range of biological activities, including immunomodulation, antibacterial, antioxidant, prebiotic, antihypertensive, antidiabetic, antitumor, and anticoagulant activities.
Evidence summary: Gastrointestinal effects (prebiotic activity, anti-inflammatory colonic actions) are supported primarily by preclinical data. Human evidence is very limited.
The RDA amount of iodine is believed to be necessary for maintenance of normal thyroid function in adults. In people with insufficient iodine in their diet, bladderwrack may serve as a supplemental source of iodine. There are significant differences in iodine content among different seaweed species. Some brown algae, especially Saccharina spp., have extremely high levels of iodine, in some cases exceeding 10,000 mg/kg dw.
Evidence summary: The role of brown algae as a source of dietary iodine is well-established. However, the iodine content is highly variable depending on species, growing location, and processing, making dosing for thyroid-related purposes unreliable without standardization.
Phytosterols such as fucosterol in brown algae exhibit various health-improving effects, especially neuroprotective and anti-inflammatory. A wide range of pharmacological properties have been recognized for Sargassum spp. extracts or isolated pure components, including anticancer, antibacterial, antifungal, antiviral, anti-inflammatory, anticoagulant, antioxidant, hypoglycaemic, hypolipidemic, antimelanogenic, anti-bone loss, hepatoprotective, and neuroprotective activities.
Multiple health benefits have been ascribed to brown seaweeds that are used traditionally as dietary components, mostly in Asia. The anti-inflammatory effects of the key polysaccharides (fucoidan, laminarin) have been demonstrated through multiple in vitro and animal pathways; robust human clinical trials confirming anti-inflammatory endpoints are not yet established.
Because "brown algae" encompasses many species and preparations, no single universal dosage is established. The following dosages are those reported in identified research sources:
Clinical trial data are limited to inform on potential therapeutic applications for F. vesiculosus specifically, with most evidence extrapolated from studies reporting on brown seaweeds generally. Clinical trials of bladderwrack are lacking to inform dosing recommendations.
Transient hypothyroidism due to excess iodine from seaweed has been reported. There are significant differences in iodine content among different seaweed species. Some brown algae, especially Saccharina spp., have extremely high levels of iodine, in some cases exceeding 10,000 mg/kg dw. This extreme variability makes consistent iodine dosing from whole-seaweed products unreliable.
The concentrations of heavy metals in edible seaweed are generally below toxic levels; however, levels of arsenic (As), cadmium (Cd), and copper (Cu) may exceed toxic levels. The European Food Safety Authority (EFSA) has requested more knowledge on the safety issues of seaweed and macroalgae consumption regarding iodine and other metals present.
EFSA assessed the relevance of seaweed and halophyte consumption to the dietary exposure to heavy metals (arsenic, cadmium, lead, and mercury) and the iodine intake in the European population. These results underline the relevance of the current consumption of seaweeds in the overall exposure to different heavy metals and in the intake of iodine, with recommendations provided for further work needed in different areas.
Regarding arsenic specifically, research has shown that the major chemical form of arsenic in kelp is the organic form, which is considered non-toxic to humans. However, inorganic arsenic levels require monitoring across species and sourcing regions.
Fucoidans possess anticoagulant and antithrombotic activity. Fucoidans have the advantage of low toxicity and oral bioavailability and are viable drug candidates; preclinical and pilot clinical trials show promising results. However, the anticoagulant properties of fucoidan mean that combinations with anticoagulant drugs (e.g., warfarin, heparin, or novel oral anticoagulants) are a potential concern warranting caution, though human data on this interaction are limited.
Effects on estrogen levels and menstrual cycle length have been reported with bladderwrack use.
Excessive consumption of seaweeds during breastfeeding should probably be avoided due to high iodine content and potential contamination with heavy metals. Information regarding safety and efficacy in pregnancy and lactation is limited.
Safety assessment and management of potentially high levels of iodine, fiber, heavy metals, and contaminants that can be present in seaweed are essential considerations. Most studies testing pharmacological activities of fucoidan still use crude or partially purified products, which is likely due to the complexity and high cost of isolation and purification techniques. This means that commercial supplement products may differ substantially from the tested preparations in clinical studies.
The biological properties of fucoidan vary depending on the species of algae, molecular weight, composition, and structure. Due to possible differences in the chemical structure, the biological effects of fucoidan proved to be noteworthy depending on the species from which it is isolated. As a fucose-containing sulfated heteropolysaccharide, fucoidan is not uniform and its structure highly differs depending on the species source of isolation. Consumers and clinicians should be aware that products labeled "brown algae" or "fucoidan" may have substantially different bioactive profiles.
Health conditions that Brown algae may help support.
Body systems that Brown algae may help support.
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