IngredientsGigartina is a genus of red macroalgae (seaweed) belonging to the phylum Rhodophyta, the class Florideophyceae, the order Gigartinales, and the family Gigartinaceae. The genus belongs to the phylum Rhodophyta and is considered an edible seaweed, characterized by a worldwide distribution, mainly in the Northeast and Southeast Atlantic and Southeast Asia. Taxonomically, the genus has undergone considerable revision through the application of molecular phylogenetics; new perspectives in the taxonomy of the Gigartinaceae (Gigartinales, Rhodophyta) were published as early as the 1993 International Seaweed Symposium. Several species that were once placed within Gigartina have since been reclassified into related genera including Mazzaella, Sarcothalia, and Chondracanthus.
Key species that remain within or are closely associated with Gigartina in the scientific and commercial literature include:
A defining biological characteristic of the genus is its isomorphic triphasic life cycle (gametophyte and tetrasporophyte are morphologically similar). Gigartina sp. has the particularity of producing different types of carrageenans depending on the stage of the life cycle, a property of high interest for industrial extraction. Specifically, in Gigartinaceae, the life cycle phase strongly disturbs carrageenan configuration: the gametophytic life cycle yields κ/ι-type carrageenans, while the tetrasporophytic life cycle yields λ-type carrageenans.
The common names for Gigartina preparations used in commerce and traditional contexts include red marine algae, grapestone, and Gigartina red algae. The genus is closely related to Chondrus crispus (Irish Moss) and products are sometimes blended or confused with it in the supplement trade.
Gigartina is commercially available in multiple forms:
The earliest known archaeological evidence of the use of seaweeds as food and medicine dates to approximately 14,000–12,000 years ago in a late Pleistocene settlement in Monte Verde, Chile. Traces of several seaweeds, specifically including Gigartina, were found together with a plant called boldo (which has hallucinogenic properties). This makes Gigartina one of the oldest documented plants used by human societies in the Americas.
The use of seaweeds as foods and traditional medicines by inhabitants of Asian coastlines was an ancient philosophy and teaching, which placed disease prevention by way of a healthy diet ahead of the treatment of various diseases by means of drugs. The health benefits of seaweeds were recognized in ancient Chinese books on herbal medicine. Notably, a viscous solution (kwanpu or hai tai) derived from the carrageenophyte Laminaria bracteata — whose current accepted name is Gigartina bracteata — was used by the Chinese for menstrual difficulties.
In the broader tradition of seaweed consumption in East Asian cultures, 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 BCE.
Indigenous and coastal communities throughout the Pacific Americas and coastal Europe incorporated carrageenophyte seaweeds including Gigartina as food staples and medicinal preparations. Seaweed was described in early texts as beneficial in diseases of the throat, especially goiter. The production of carrageenan as a gelling agent from related species in the Gigartinaceae family has its industrial roots in Ireland (where Chondrus crispus, or Irish Moss, was harvested from the Atlantic), with practices likely mirroring traditional preparations of Gigartina along Pacific coasts.
Red algae are mostly composed of sulfated galactans such as agars or carrageenans, which are not found in land plants. Carrageenans are sulfated linear galactans with the basic structural units of carrabiose disaccharides, which consist of alternating β-1,3- and α-1,4-linked galactose residues. The variations in its basic structure are determined by the occurrence of 3,6-anhydrogalactose and the location and number of sulfate groups in the linked galactose residues.
Carrageenans are highly sulfated polysaccharides (20–50%) and the α-D-galactopyranosyl residues may be in 3,6-anhydro form. Depending on the number and position of sulfate-ester groups on the repeating disaccharide, several types are distinguished: kappa-carrageenans (one sulfate-ester group), iota-carrageenans (two sulfate-ester groups), and lambda-carrageenans (three sulfate-ester groups).
Iota-carrageenan is a soft-gel forming sulfated galactose-based polysaccharide predominantly extracted from red seaweed, including Gigartina stellata and Chondrus crispus. Lambda-carrageenan is extracted from tetrasporic plants of the red seaweed Gigartina skottsbergii (Gigartinaceae, Rhodophyta), abundant in Patagonian areas, and has a very high sulfate content with only trace amounts of 3,6-anhydrogalactose.
The molecular weight of carrageenan fractions is substantial: the galactose-based polysaccharides can have a molecular weight ranging from about 15 kDa to 5 MDa, with fractions of particular interest having average molecular weights in the range of 50 kDa to 3 MDa. The physicochemical properties of κ, κ/β, κ/ι, and λ-carrageenans from red algae of the Gigartinaceae have been analyzed and compared; the highest molecular weights (527 kDa) and negative electrokinetic potentials (–36.4 mV) were obtained for λ-carrageenan, which had the conformation of a disordered coil.
Carrageenan content in Gigartina varies by species, life cycle phase, and season. The maximum carrageenan content in G. pistillata was obtained from female gametophyte samples at 59.7% of dry weight in late spring.
The polysaccharides of the genus Gigartina have already shown promising results against human diseases. However, other compounds from this genus are also being studied, including phenols and pigments, due to their bioactive properties.
As a red alga, Gigartina also contains:
The biological properties and pharmacological activity of carrageenans may depend on their primary structure, number and location of the sulfated groups, and degree of molecular polymerization, as well as on the conformation of macromolecules in solution. Numerous structural features contribute to the various bioactivities of carrageenans, including antioxidant, antitumor, immunomodulatory, anti-inflammatory, anticoagulant, antiviral, antibacterial, antifungal, and antihyperlipemic activities.
Antiherpetic activity has been directly correlated to the amount of α-D-galactose 2,6-disulfate residues in the natural carrageenans. Conversely, the cyclization of the α-D-galactose 6-sulfate and 2,6-disulfate units into 3,6-anhydro-α-D-galactose residues in these polysaccharides generally lowers the antiherpetic activity of the derivatives.
The most extensively documented bioactivity of Gigartina carrageenans is their inhibitory effect against herpes viruses. Natural carrageenans of diverse structural types isolated from the red seaweed Gigartina skottsbergii have been identified as potent and selective inhibitors of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2).
In vitro studies: The lambda-carrageenan 1T1, the kappa/iota-carrageenan 1C1, and the mu/nu-type 1C3 isolated from Gigartina skottsbergii proved to be potent and selective inhibitors of HSV types 1 and 2. The antiviral IC₅₀ values determined by virus yield inhibition assay in different cell lines ranged from 0.4 to 3.3 μg/mL, and no cytotoxic effects were measured by trypan blue exclusion on stationary or proliferating cells. Lambda-carrageenans and the partially cyclized mu/nu-carrageenan were the most potent inhibitors of herpes viruses, including acyclovir-resistant variants and clinical isolates, with IC₅₀ values lower than 1 μg/mL against both serotypes and selectivity indices higher than 10³. Kappa/iota-carrageenans were slightly less effective, with IC₅₀ values in the range 1.6–4.1 μg/mL.
Animal (murine) studies: The partially cyclized mu/nu-carrageenan 1C3 isolated from Gigartina skottsbergii was previously shown to be a potent inhibitor of HSV-1 and HSV-2 in vitro. In a murine model of intraperitoneal HSV-1 infection, when 30 mg/kg of body weight of 1C3 was administered intraperitoneally immediately after HSV-1 infection, 87.5% survival of the animals was achieved (p < 0.005), associated with a delay in the mean day of death. Animal survival was not improved when multiple doses were also given in the 1–48 hours post-infection period, and no protection was afforded when treatment was started after 24 hours of infection.
A lambda-carrageenan extracted from the red seaweed Gigartina skottsbergii was also evaluated in a murine model of herpes simplex virus type 2 (HSV-2) genital infection, demonstrating protective effects.
Breadth of antiviral activity: It has been demonstrated that carrageenans from Gigartina have antiviral activity against human herpesvirus type 1 and type 2 (HSV-1, HSV-2), and human cytomegalovirus (CMV). One study also reported a lambda-carrageenan from Gigartina skottsbergii as the first of its type to demonstrate antiviral activity against animal viruses belonging to the Alphaherpesvirinae subfamily, bovine herpesvirus type 1 (BoHV-1) and suid herpesvirus type 1 (SuHV-1), with lambda-carrageenan able to reduce infectivity of both viruses with a more pronounced effect against BoHV-1.
Limitations: The antiviral evidence for Gigartina specifically against herpes viruses is predominantly from in vitro cell culture studies and rodent models. No published randomized controlled trials in human subjects exist evaluating oral or topical Gigartina preparations specifically against HSV infection. The evidence therefore remains preclinical.
The most robust human clinical evidence related to carrageenan — the primary bioactive constituent of Gigartina — concerns iota-carrageenan in nasal spray formulations for viral upper respiratory tract infections. Although this specific clinical research was conducted using pharmaceutical-grade iota-carrageenan (not always explicitly sourced from Gigartina), the carrageenan is the same class of sulfated polysaccharide found in Gigartina.
Exploratory RCT: In a randomized, double-blind, placebo-controlled exploratory trial, 35 human subjects suffering from early symptoms of common cold received iota-carrageenan (0.12%) in a saline solution three times daily for 4 days, compared to placebo. Administration of iota-carrageenan nasal spray reduced the symptoms of common cold (p = 0.046) and the viral load in nasal lavages (p = 0.009) in patients with early symptoms.
Larger RCT: In a randomized, double-blind, placebo-controlled trial, 211 patients suffering from early symptoms of the common cold were treated for seven days, applied three times daily with either a carrageenan-supplemented nasal spray or saline solution as placebo, with an overall observation period of 21 days. In adults with common cold virus infections, direct local administration of carrageenan with nasal sprays reduced the duration of cold symptoms. A significant reduction of viral load in the nasal wash fluids of patients confirmed similar findings from earlier trials in children and adults.
Pooled individual patient data analysis: Individual patient data were analyzed from two randomized double-blind placebo-controlled trials assessing the therapeutic effectiveness of carrageenan nasal spray in acute common cold, including patients with virus-confirmed common cold (n = 254; verum 126, placebo 128). Carrageenan-treated patients showed a significant reduction in duration of disease of almost 2 days (p < 0.05) as well as significantly fewer relapses during 21 days of observation period (p < 0.05). Virus clearance between visit 1 and visit 2 was significantly more pronounced in the carrageenan group (p < 0.05). In both studies, virus-confirmed common cold was caused by three main virus subtypes: human rhinovirus (46%), human coronavirus (25%), and influenza A (14%) virus. Carrageenan nasal spray showed significant antiviral efficacy in all three virus subgroups; the highest effectiveness was observed in human coronavirus-infected patients. The reduced duration of disease was 3 days (p < 0.01) and the number of relapses was three times less (p < 0.01) in carrageenan-treated coronavirus-infected patients.
Evidence strength: Multiple randomized, double-blind, placebo-controlled trials with direct viral load measurements support iota-carrageenan nasal spray for reducing duration and viral load in common cold. The evidence is moderate strength and clinically meaningful for the upper respiratory application, though most trials are relatively small and the carrageenan source is typically pharmaceutical-grade rather than whole Gigartina preparations.
Antioxidant properties of structurally different sulfated polysaccharides (carrageenans) have been studied in vitro and ex vivo. Ferric reducing antioxidant activity and inhibitory effects on hydroxyl radicals and superoxide anion radicals were demonstrated in vitro, with activity depending on the polysaccharide structure. Carrageenans also stimulate catalytic activity of superoxide dismutase (SOD) from donor erythrocytes.
Regarding Gigartina-specific antioxidant research: The antioxidant activity toward peroxyl radicals was higher for commercial λ-carrageenan (consistent with its higher sulfate content). The kinetics of the reaction of both polysaccharides with hydroxyl and ABTS⁺ radicals showed a complex mechanism, but the antioxidant activity was higher for the polysaccharide from the green variant of tetrasporic Gigartina skottsbergii.
Evidence strength: In vitro and ex vivo only; no human clinical trials specifically examining antioxidant effects of Gigartina-derived preparations have been published in the peer-reviewed literature.
Since the 1960s, carrageenan anticoagulant and antithrombotic activity has been studied, with λ-carrageenan showing higher anticoagulant potential than κ-carrageenan. Research using Gigartina skottsbergii carrageenans confirmed this: antiherpetic and anticoagulant properties of carrageenans from the red seaweed Gigartina skottsbergii and their cyclized derivatives were correlated with structure and biological activity.
Antioxidant, anticoagulant, and immunostimulating activities of native and modified polysaccharides from Gigartina have been assayed in vitro. The oversulfated derivatives showed high antioxidant capacity toward oxygen radical assay; oversulfated polysaccharides presented higher antioxidant capacity toward hydroxyl radicals than the native polysaccharide.
Carrageenans from Gigartina and related genera have diverse activities, including immunomodulatory, anticoagulant, antithrombotic, antiviral, and antitumor effects.
Evidence strength: In vitro studies demonstrate anticoagulant activity. No human clinical studies have assessed anticoagulant effects of Gigartina-specific preparations.
Several studies have shown that carrageenan has immunomodulatory and antitumor activity. The antitumor activity of carrageenan could be related to the destabilization of the interaction of the glycosaminoglycans (GAGs) portion of the proteoglycans and the extracellular matrix proteins, thus eliminating the adhesion of cancer cells to matrices, which is necessary for the spread of metastasis.
Gigartina-specific in vitro evidence: A study published in Marine Drugs (2020) directly investigated the antitumor potential of Gigartina pistillata carrageenans: G. pistillata is a red seaweed common in Figueira da Foz, Portugal. The antitumour potential of G. pistillata carrageenan from the female gametophyte (FG) and tetrasporophyte (T) life cycle stages was evaluated against colorectal cancer stem cell (CSC)-enriched tumourspheres. FTIR-ATR analysis indicated differences between life cycle phases: FG yielded a κ/ι hybrid carrageenan and T a λ/ξ hybrid. Both carrageenan extracts presented IC₅₀ values inferior to 1 μg/mL in HT29-derived CSC-enriched tumourspheres, as well as reduced tumoursphere area. The two extracts were also effective at reducing cellular viability in SW620- and SW480-derived tumourspheres. These results indicate that carrageenans extracted from two G. pistillata life cycle phases have antitumour potential against colorectal cancer stem-like cells, especially the T carrageenan.
It has also been demonstrated that carrageenans can delay cell cycle progression in HeLa cells, where λ-carrageenans prolonged cell cycle by stalling in G1 and G2/M phases, presenting a strong antiproliferative activity by preventing cellular division.
Research using λ-carrageenan oligosaccharides (COS) in animal models of gastric carcinoma found that λ-COS alone did not have a significant impact on BGC-823 cells in vitro; however, it was effective in inhibiting tumor growth in vivo. When THP-1 cells were pre-incubated with λ-COS and used to condition the medium, BGC-823 cells in vitro displayed a concentration-dependent induction of cell apoptosis, nuclear damage, and collapse of mitochondrial transmembrane potential. These findings suggested that the antineoplastic effect of λ-COS was primarily due to its immunoenhancement property.
A preclinical study in tumor-bearing mice found that intratumoral injection of λ-carrageenan could inhibit tumor growth in B16-F10 and 4T1 bearing mice and enhance tumor immune response by increasing the number of tumor-infiltrating M1 macrophages, dendritic cells, and more activated CD4+CD8+ T lymphocytes in the spleen. λ-Carrageenan could enhance the secretion of IL-17A in spleen and significantly increase the level of TNF-α in tumor. Moreover, λ-carrageenan exhibited an efficient adjuvant effect in OVA-based preventative and therapeutic vaccine for cancer treatment.
Evidence strength: Exclusively in vitro and animal model data. No human clinical trials have assessed Gigartina-derived carrageenans for cancer treatment or prevention. This area is exploratory/preliminary.
Biological properties of carrageenan polysaccharides including antiviral, immunomodulatory, anticoagulant, antioxidant, and anticancer properties have been broadly studied. The immunomodulatory mechanism has been characterized at a cellular level: the ability of carrageenan polyelectrolyte complexes to induce the synthesis of pro-inflammatory cytokines (TNF-α) and anti-inflammatory cytokines (IL-10) in peripheral blood mononuclear cells was determined by the activity of κ-carrageenan, regardless of composition.
Evidence strength: Primarily in vitro and animal studies. Immunomodulatory effects have not been formally evaluated in human clinical trials specifically for whole Gigartina preparations.
The following dosages and administration routes are drawn directly from published research:
No standardized oral supplemental dose of whole Gigartina seaweed has been established in clinical trials. The dosages referenced above apply to isolated, pharmaceutical-grade carrageenan fractions. Supplement products commonly sold as "red marine algae" or "Gigartina" in capsule form do not have established doses from controlled human studies.
The U.S. Food and Drug Administration (FDA) approved carrageenan as a safe, direct food additive for human consumption in 1961, and in 1969 the Joint FAO/WHO Expert Committee on Food Additives (JECFA) reviewed carrageenan and found it suitable for use in food. The European Food Safety Authority (EFSA) similarly approved carrageenan as a food additive (E407) following comprehensive toxicological reviews.
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has maintained a group ADI "not specified" for carrageenan and processed Eucheuma seaweed — an indication of safety at typical use levels. JECFA also concluded that use of carrageenan in infant formula at concentrations up to 1000 mg/L is not of concern.
Confusion exists in the literature due to using the name "carrageenan" when the actual product tested is another material, degraded carrageenan (poligeenan). Degraded carrageenan (poligeenan) may cause adverse effects in animal studies and is NOT permitted to be used as a food additive.
In 1983, the International Agency for Research on Cancer (IARC) classified degraded carrageenan as a cancer risk to humans. The IARC's determination came about after several research studies found that rats fed degraded carrageenan developed colorectal cancer. Carrageenan and degraded carrageenan are not the same substance. Degraded carrageenan, officially known as poligeenan, is formed from carrageenan that has been exposed to high temperatures and acid hydrolysis.
The undegraded, food-grade carrageenan used in commercial products differs significantly from degraded carrageenan (poligeenan), which was withdrawn from use due to safety concerns. JECFA reviews in 2008 and subsequent years found no basis for safety concerns when assessing properly characterized food-grade material.
Scientists petitioning for carrageenan to be dropped from the FDA GRAS list believe that even food-grade carrageenan can become degraded and turn into poligeenan after it comes into contact with acid in the stomach. Yet, studies have shown that 98–100% of carrageenan is excreted in the stools without significant degradation by stomach acid or bacteria, though it remains probable that a small amount of carrageenan is degraded in the gastrointestinal tract.
A 2018 review found no adverse effect of food-grade carrageenan on human health. Carrageenan-containing products should not be contaminated with more than five percent (considered a safe level) of degraded carrageenan.
Some research suggests that carrageenan may trigger inflammation, gastrointestinal ulcerations, and damage to the digestive system. These concerns, arising primarily from animal model data using higher-dose or degraded carrageenan preparations, remain the subject of scientific debate. Some people may experience side effects such as bloating, digestive issues, or allergic reactions from carrageenan.
Given the documented in vitro anticoagulant activity of λ-carrageenan fractions from Gigartina, a theoretically relevant interaction with anticoagulant or antiplatelet drugs (such as warfarin, heparin, or aspirin) exists. However, no human pharmacokinetic or pharmacodynamic drug-interaction studies with Gigartina-specific preparations have been published in the peer-reviewed literature. The clinical significance of this potential interaction at supplement doses is unknown.
As with all seaweeds, Gigartina preparations contain iodine. High intakes of iodine-containing seaweeds can affect thyroid function in susceptible individuals, including those with pre-existing thyroid disease or those taking thyroid medications.
Iota-carrageenan is broadly active against respiratory viruses in vitro and has an excellent safety profile based on the clinical trials conducted. No serious adverse events attributed to iota-carrageenan nasal spray were reported across the published trials.
In 2016, the National Organic Standards Board (NOSB) recommended removing carrageenan from the National List; however, in April 2018 the USDA issued its final rule keeping carrageenan on the list of allowed substances in organic processing, noting its functionality and lack of adequate broad substitutes.
Health conditions that Gigartina may help support.
Body systems that Gigartina may help support.
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