IngredientsAlginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. Also known as alginic acid, it is a kind of natural linear anionic polysaccharide, and is mainly distributed in the cell wall of brown algae. It is a hydrophilic colloid carbohydrate that occurs naturally in the cell walls and intercellular spaces of various species of brown seaweed (Phaeophyceae).
Alginic acid is a family of natural copolymers of β-D-mannuronic acid and α-L-guluronic acid. More specifically, this is a block copolymer including a homopolymer fraction of D-mannuronic acid (MM fraction), a homopolymer fraction of L-guluronic acid (GG fraction), and a fraction of randomly arranged D-mannuronic acid and L-guluronic acid (M/G fraction) in arbitrary combination. The chains contain three distinct regions: in one, the D-mannuronic acid units alternate with L-guluronic acid units, whereas the remaining regions are homogeneous and contain either D-mannuronic acid or L-guluronic acid.
It is hydrophilic and forms a viscous gum when hydrated. When the alginic acid binds with sodium and calcium ions, the resulting salts are known as alginates. Its colour ranges from white to yellowish-brown, and it is sold in filamentous, granular, or powdered forms.
The alginate content can reach 50% of the algae mass. Commercial grade alginate is extracted from giant kelp Macrocystis pyrifera, Ascophyllum nodosum, and types of Laminaria. Alginic acid is commercially extracted from alginates from species that include Ascophyllum (North Atlantic), Laminaria and Saccharina (various northern hemisphere), Durvillea (Australia), Ecklonia (South Africa), Sargassum, and Turbinaria.
Alginates are also produced by two bacterial genera Pseudomonas and Azotobacter, which played a major role in the unravelling of the biosynthesis pathway; bacterial alginates are useful for the production of micro- or nanostructures suitable for medical applications. Depending upon the source, alginate may vary in composition, occurring with differing ratios of mannuronate to guluronate.
Alginates are the salts of alginic acid that provide the structural components of brown seaweed. In order to extract alginic acid from these salts, ion exchange is induced in an alkali medium followed by precipitation and purification. The manufacturing process used to extract sodium alginates from brown seaweed falls into two categories: (1) the calcium alginate method, where the brown seaweed is first treated with calcium chloride to form a calcium alginate intermediate before washing with hydrochloric acid, and (2) the alginic acid method, where there is no calcium alginate intermediate and the brown seaweed is treated only with hydrochloric acid.
While alginic acid itself was not isolated and identified until the late 19th century, its source — brown seaweed — has a long history of medicinal use across many coastal cultures. In Traditional Chinese Medicine, seaweeds like kelp (昆布, kombu) were used to soften masses, resolve phlegm, and treat thyroid enlargement (goiter) due to their iodine content and mucilaginous properties. In Japanese, Korean, and European folk practices, brown algae were commonly consumed to promote digestion, detoxification, and hydration, and used topically for wound healing and skin conditions. In Irish and Scottish coastal traditions, species of brown algae were used in broths and poultices, especially for their demulcent and mineral-rich qualities.
Algin was discovered in 1881 by an English chemist, E. C. C. Stanford, who obtained a viscous mucilage by extracting Laminaria stenophylla with alkali; he called the product "algin." He further found that, if a mineral acid was added, a gelatinous precipitate was obtained, which dried to a hard, horny substance — he identified this as a new acid which he named "alginic acid." Later, Stanford started manufacturing algin on a commercial scale in Scotland. In 1927, Thornley set up a company to produce alginate in San Diego, USA, which in 1929 was reorganized into the Kelco Company.
The algae has traditionally been used as a food additive, thickener, and anti-inflammatory agent and has also been included in over-the-counter antacids for several decades.
Alginic acids are a group of polysaccharides formed by residues of β-D-mannuronic and α-L-guluronic acids, which build M- and G-blocks, respectively. The ratio between these structural units is often 1:1; however, there are exceptions.
Alginates are capable of forming strong gels, in particular with calcium ions (egg-box structures), due to the presence of G-blocks and their specific conformation. Aqueous solutions of the sodium salt of alginate gel upon contact with calcium ion to form a stable elastic gel. The G-rich regions of the polymer determine gel firmness: alginates from different species of brown seaweed vary in their chemical structure, resulting in different physical properties; some species yield an alginate that gives a strong gel, another a weaker gel, some may produce a cream or white alginate, while others are difficult to gel and are best used for technical applications.
Alginate has carboxyl groups which are charged at pH values higher than 3–4, making alginate soluble at neutral and alkaline conditions. In acidic environments, alginate carboxyl groups are protonated, thereby limiting drug release. This pH-dependent behaviour underpins both its raft-forming action in the stomach and its utility as a pharmaceutical excipient.
Owing to the free hydroxyl and carboxyl groups, alginate also has excellent bio-adhesion. It is particularly useful as a biomaterial because of its nontoxicity, hygroscopicity, and biocompatibility, and can imitate local bioenvironments; its degradation product can be easily cleared by the kidneys.
Alginic acid derivatives, or alginates, treat GERD via a unique mechanism by creating a mechanical barrier that displaces the postprandial acid pocket. In the presence of gastric acid, they precipitate into a gel and form a raft that localizes to the acid pocket in the proximal stomach. The acid pocket forms at the gastroesophageal junction after a meal and consists of an unbuffered, highly acidic gastric juice and has pathophysiological relevance in GERD; a strong alginate raft can cap the acid pocket and reduce or even prevent postprandial acid reflux.
Alginate can remove both pepsin and bile acids from gastric refluxate, limiting their diffusion and specifically affecting the enzymatic activity of pepsin. Alginates play a major role in the topical protection of the vulnerable and sensitive esophageal mucosa, reducing the risk of inflammation as a result of the components of the gastric refluxate; suspensions of the correct sodium alginate can form adherent viscous layers on contact with the esophageal mucosa and demonstrate bioadhesive potential in this area.
Depending on the specifics of the alginate formulation, the gel matrix formed can have up to 1,400 times the viscosity of water. This barrier is created swiftly, typically within seconds of administration, and can persist in the stomach for several hours.
Several mechanisms have been suggested for the positive effects observed, which involve delayed gastric emptying, increased viscosity of digesta, and slowed nutrient absorption in the small intestine upon alginate gel formation. Seaweeds and seaweed extract can be used as functional ingredients by modifying the nutrient composition to reduce the proportion of available carbohydrates, delaying the gastric emptying time and the absorption rate of glucose by increasing the digesta viscosity, and attenuating the digesting rate by blocking the activity of digestive enzymes.
Alginic acid is able to absorb and chemically bind sodium and other cations when prepared or ingested. The defining properties of alginates are structural and sorption, which determine their practical application as sorbents and functional materials.
Sodium alginate has been shown to possess a variety of biological activities, such as antitumor, antihypertension and antiobesity effects, and to reduce blood lipids and postprandial blood glucose. Alginates demonstrate biological activities per se, including anti-hyperlipidemic, antimicrobial, anti-reflux, immunomodulatory, and anti-inflammatory activities.
The use of alginic acid and its salts in GERD is the most extensively studied clinical application, with a substantial body of evidence from randomised controlled trials (RCTs) and multiple meta-analyses.
Alginates are medications that work through an alternative mechanism by displacing the postprandial gastric acid pocket. A systematic review and meta-analysis examined the benefit of alginate-containing compounds in the treatment of patients with GERD symptoms by searching PubMed/MEDLINE, Embase, and the Cochrane library electronic databases through October 2015 for RCTs comparing alginate-containing compounds to placebo, antacids, H2RAs, or PPIs.
Data from the available clinical trials support the efficacy of alginates for the treatment of symptomatic GERD; they were superior to placebo and antacids.
A further systematic review and meta-analysis included ten articles with eleven RCTs; qualitative analysis of four trials indicated better outcomes with alginates versus placebo/antacids.
In vitro and in vivo studies have demonstrated an immediate onset of therapeutic effects with alginate (within 1 hour of administration) that is faster than that of a PPI or an H2 receptor antagonist.
An "acid pocket" has been described in the proximal stomach, particularly evident postprandially in GERD patients. By creating a low-density gel "raft" that floats on top of gastric contents, alginate-antacid formulations may neutralize the "acid pocket." The hypothesis that the postprandial "acid pocket" can be displaced distal to the esophagogastric junction (EGJ) by an alginate-antacid formulation was studied in ten symptomatic GERD patients. Gaviscon (the tested alginate-antacid formulation) was found to eliminate the "acid pocket" in GERD patients; this effect was likely attributable to the alginate "raft" displacing gastric contents away from the EGJ, suggesting the formulation to be a well-targeted postprandial GERD therapy.
The effect of an alginate-antacid combination was above and beyond that of antacid after the first 30 minutes and persisted for at least 2.5 hours after the meal.
Alginates also show efficacy in laryngopharyngeal reflux (LPR). A non-inferiority randomized controlled trial investigated an alginate suspension (Gastrotuss®) compared to PPIs (Omeprazole) in reducing LPR symptoms and signs; 50 patients with laryngopharyngeal symptoms were randomized to either Gastrotuss® (20 ml, three daily doses) or Omeprazole (20 mg, once daily). From pre- to 2-month post-treatment, the mean Reflux Symptom Index (RSI) significantly decreased in the alginate group and PPI group, supporting the non-inferiority of Gastrotuss® to PPIs in the improvement of LPR symptoms and signs.
A large real-world evidence study in India found that patients who received sodium alginate antacid suspension (10–20 ml, 3–4 times daily) for one week reported clinically meaningful improvement in heartburn, regurgitation, and overall symptoms. According to the physicians, sodium alginate antacid was effective in 96.64% (4,058 out of 4,199) of patients.
Alginate has been viewed as an attractive option because it has limited systemic absorption, creates a raft-like protective barrier to limit reflux, and neutralizes the acid pocket after a meal; a position paper from the Romanian Society of Neurogastroenterology reported that an alginate-antacid combination was superior to both placebos and antacids to treat mild reflux symptoms and could be used to treat persistent reflux symptoms alongside PPI therapy.
Evidence strength: Moderate-to-strong. Multiple RCTs and meta-analyses consistently demonstrate superiority to placebo and antacids in symptomatic GERD. Alginates show non-inferiority to PPIs in some comparisons. Limitations include heterogeneity across formulations and the fact that results from one specific alginate suspension cannot necessarily be generalized to all commercially available products.
A review of human and animal studies investigating the effect of alginate supplementation on appetite regulation, glycaemic and insulinaemic responses, and lipid metabolism found that the majority of animal and human studies suggest that alginate consumption does suppress satiety and to some extent energy intake; however, only one long-term intervention trial found effects on weight loss.
Data from dietary interventions show that alginates have potential applications in weight management and satiety effects for humans.
According to a double-blind, randomised trial, apparent weight loss in overweight subjects with alginate was noted; however, the weight loss in normal-weight subjects with alginate was insignificant compared to maltodextrin.
Evidence strength: Preliminary. Effects on satiety have been seen in a majority of human studies, but clinical trials show inconsistent results on actual weight loss. A single long-term RCT reported weight-loss effects. Larger, better-controlled trials are needed.
In addition to satiety effects, alginates seem to exhibit beneficial influence on postprandial glucose absorption and insulin response in animals and humans.
In a randomised double-blind crossover trial, peak blood glucose levels were reduced by 11% and 15%, respectively, in groups that received noodles containing 5% or 8% calcium alginate compared to the control meal without alginate; there was also a 15% and 21% reduction in the area under the glucose curve. A pre-load beverage fortified with sodium alginate extract (15 g) attenuated the postprandial glucose excursion after a subsequent meal by 40%.
Sodium alginate was known to reduce postprandial glucose in both acute animal experiments and human trials. Previous studies showed that sodium alginates of different molecular weights reduced postprandial glucose differently.
Evidence strength: Moderate (for acute effects). Short-term human clinical trials consistently show reductions in postprandial glucose and area under the glucose curve. However, evidence regarding long-term glycaemic control and clinical applicability in diabetes management remains limited, with most mechanistic data from animal studies.
Alginate supplementation was only found to have cholesterol-lowering properties in animals; as of the reviewed literature, no equivalent effect was confirmed in human clinical trials.
Alginate, as a dietary fibre, enhanced bile acid excretion in an overweight human trial, suggesting a mechanism for lipid modulation. However, studies on associations between alginate and bile acids were mostly limited to animal experiments.
Evidence strength: Weak in humans. Cholesterol-lowering and lipid-modulating effects are demonstrated in animal models, with very limited human data supporting this application.
The effect of sodium alginate on the gastrointestinal absorption of the tracers strontium-85 and calcium-47 was investigated in 19 human subjects. 1.5 g of alginate reduced the absorption of strontium by a factor of two with no significant effect on calcium absorption; the smaller dose (0.3 g) appeared to have no effect on strontium or calcium absorption, and the larger dose (3.0 g) had no greater effect than the 1.5 g dose.
Algin has been investigated for decreasing the absorption of certain heavy chemicals by the body, including strontium, barium, tin, cadmium, manganese, and zinc.
Evidence strength: Moderate in the specific context of radioactive strontium reduction; human studies are small and dated (mid-20th century). Evidence for other heavy metals comes mostly from in vitro and animal models.
Alginate applications span various fields, including wound healing dressings and heavy metal chelation. Alginates have numerous applications in pharmaceutical technology including micro- and nanoparticles, tablets, mucoadhesive dosage forms, wound dressings, and films.
Evidence strength: The use of calcium alginate fibres and dressings in wound care is well-established in clinical practice and supported by numerous studies; however, as these are primarily device applications rather than dietary supplementation, the detailed clinical trial literature for topical wound healing is separate from the oral supplementation evidence base.
In a double-blind, randomised trial in overweight subjects, the relative abundance of Firmicutes tended to decrease and Proteobacteria increased with alginate supplementation, similar to outcomes in overweight and obese adults after dietary and surgical intervention; alterations in gut microbiota induced by alginate were similar to those after bariatric surgeries, which was associated with inhibited intestinal absorption.
Evidence strength: Preliminary. Microbiota modulation data in humans are very limited and come from single trials; most mechanistic data are from animal models.
Commercially, alginates are available as alginic acid (the free acid form) or as salts — most commonly sodium alginate, potassium alginate, calcium alginate, or magnesium alginate. It is sold in filamentous, granular, or powdered forms.
Pharmaceutical technology applications include micro- and nanoparticles, tablets, mucoadhesive dosage forms, wound dressings, and films.
Doses used in key studies include the following:
Alginic acid is recognized as GRAS (Generally Recognized As Safe) by the FDA and is approved for human consumption. EFSA, in its 2017 reassessment, confirmed that sodium alginate poses no safety concerns as a food additive, with no need to set an Acceptable Daily Intake (ADI), indicating a very high safety margin; however, it recommended that intake in infants remain below therapeutic dosage levels. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) set its ADI in 1992 as "not specified," meaning no specific limit is necessary due to its safety.
Alginic acid and its sodium and calcium salts are regarded as generally non-toxic and biocompatible. Its degradation product can be easily cleared by the kidneys. Alginate has limited systemic absorption.
In the large Indian real-world study, adverse effects were reported in 2.22% (139 out of 6,246 patients); overall, no serious adverse reactions were reported.
Since alginates are obtained from a natural source, a variety of impurities may potentially be present, including heavy metals, proteins, and endotoxins; for pharmaceutical applications, particularly for parenteral administration, these impurities should be removed.
A monograph for alginic acid is included in the European Pharmacopoeia (Ph.Eur.); ultrapure grades of alginates have a controllable level of pyrogenicity and may be used as implants in combination with drugs.
The ADI of "non-specified" is assigned to food substances with low toxicity in consideration of both available data and the total dietary intake of the substance when used at levels required to achieve a desired effect; there is, however, a risk from the ingestion of large quantities of alginic acid, including risk of intestinal obstruction.
Alginate products containing sodium, potassium, calcium, or magnesium salts should be used cautiously in patients with significant renal impairment, as the kidneys may not efficiently excrete excess electrolytes.
The gel-forming property that gives alginic acid its therapeutic utility can also delay or reduce the absorption of concurrently administered oral medications. For some drugs which require greater protection with preferential absorption in the intestinal tract or other conditions such as modified drug release, alginate is a preferable polymer; its solubility and pH sensitivity make alginate a good biomaterial for drug-delivery systems. When alginic acid-containing products are taken at the same time as other oral medications, the physical barrier formed may slow or diminish drug absorption.
1.5 g of sodium alginate reduced the absorption of strontium by a factor of two, but with no significant effect on calcium absorption. This differential effect on divalent cation absorption indicates that co-administration with mineral supplements or medications dependent on divalent cation uptake requires consideration of timing.
Health conditions that Alginic acid may help support.
Alginic acid formulations are clinically used to relieve symptoms of GERD including heartburn, regurgitation, and upper abdominal discomfort. Multiple RCTs and multicenter studies confirm superiority over placebo and comparability with standard antacid therapy. The raft-forming mechanism physically prevents acid from reaching the esophagus and stomach.
Alginic acid is the free-acid form of alginate used in raft-forming antireflux therapy. It forms a floating polymer gel in the stomach that physically blocks acid reflux into the esophagus. A PMC review (PMC6836317) extensively documents its mechanism and supporting clinical evidence. A meta-analysis of 14 RCTs (n=2,095) supports alginate-class efficacy for GERD symptom resolution. The 2025 MDPI GERD review validates alginic acid as having clinical evidence for GERD management.
Alginate forms a viscous gel in the stomach that can promote satiety and reduce energy intake in acute settings. Several human trials show reduced postprandial hunger ratings, though long-term effects on appetite are inconsistent. A 2013 systematic review concluded most human studies support some suppression of satiety and energy intake depending on formulation.
Multiple human clinical trials demonstrate that calcium alginate and sodium alginate reduce postprandial blood glucose levels. The mechanism involves inhibition of α-glucosidase and maltase activity, slowing starch digestion. Evidence spans healthy adults and type 2 diabetic populations.
Alginate inhibits pancreatic lipase activity and can bind bile acids and dietary cholesterol in the small intestine, potentially reducing cholesterol absorption. Evidence from a 2013 systematic review confirms some cholesterol-lowering activity in animal studies, while human evidence remains limited and mixed.
Alginate acts as a prebiotic substrate for select gut bacteria, promoting SCFA production (acetate, propionate, butyrate) and enriching beneficial microbes such as Bifidobacterium animalis. Human and animal data support compositional shifts in the microbiome following alginate supplementation. Its oligosaccharide derivatives (AOS) have been particularly studied.
Alginate supplementation as an adjunct to energy restriction has been shown in at least one well-designed RCT to improve weight loss in obese subjects. Additional mechanisms include inhibition of pancreatic lipase and modulation of gut microbiota linked to obesity-related metabolism. Evidence across longer-term trials is limited but promising.
Alginic acid and alginates bind heavy metal cations (e.g., lead, cadmium, strontium) through ion-exchange mechanisms in the gastrointestinal tract. Because alginate is not absorbed by the gut, it is excreted together with bound metals. This sequestration capacity is well-documented in biochemical and some in vivo studies.
Alginate and alginate oligosaccharides have been shown in animal models and preliminary human protocol evidence to ameliorate intestinal inflammation in IBD, particularly ulcerative colitis. The mechanism is microbiota-dependent, involving enrichment of Bifidobacterium animalis and altered bile acid metabolism. Human trial protocols have been registered.
Alginate-based dressings have demonstrated clinical efficacy in managing chronic skin ulcers including diabetic foot ulcers and pressure ulcers. Internally, alginic acid forms a raft barrier protecting the gastric and esophageal mucosa from acid-related damage. Both topical and oral applications have RCT-level evidence.
Alginate dressings are well-established clinical tools for wound healing, particularly for chronic exuding wounds. They maintain a moist wound environment, support angiogenesis and tissue regeneration, and have RCT evidence for pressure ulcers, diabetic foot ulcers, and venous leg ulcers.
Body systems that Alginic acid may help support.
Go back