IngredientsLithothamnion is a genus of thalloid red algae belonging to the division Rhodophyta. It comprises 103 species, whose members are known by a number of common names. Taxonomically, the genus is classified within the kingdom Eukaryota, phylum Rhodophyta, class Florideophyceae, order Hapalidiales, and family Hapalidiaceae. The two species of greatest commercial and nutritional significance are Lithothamnion calcareum (Pallas) Areschoug and Lithothamnion corallioides (P.Crouan & H.Crouan) P.Crouan & H.Crouan. A closely related species, Phymatolithon calcareum, is frequently treated as a synonym of L. calcareum in the commercial literature.
Nomenclature in this genus has been historically complex. The name Lithothamnion corallioides is currently regarded by some authorities as a synonym of Boreolithothamnion corallioides (P.Crouan & H.Crouan) V.Peña & P.W.Gabrielson. In commercial and regulatory contexts, the genus name is frequently spelled Lithothamnium (with a terminal -ium), a variant used interchangeably in older literature and product labeling. The supplement trade name Aquamin (Marigot Ltd., Ireland) designates a standardized multi-mineral extract derived from Lithothamnion species harvested in the North Atlantic.
Lithothamnion calcareum is a red alga of the Corallinaceae family whose main feature is the formation of calcium carbonate precipitate in its cell walls. These plants lay down calcium carbonate in their cell walls, which gives them a hard, stony texture. Living corallinaceae generally show a red colour due to the presence of the pigment phycoerythrin in their structure. When dead, the colour is white or yellowish.
A number of crustose, calcareous red algae (Corallinaceae) grow detached in shallow waters and accumulate to form large beds on the coasts of north-western Europe and in the western Mediterranean, México (Baja California), and Brazil. These are collectively known as "maërl," "coral," or "coral sand" in north-western France, Britain, and Ireland. Scientifically, they are also known as "rhodoliths."
The two most common species in the north-eastern Atlantic are Phymatolithon calcareum and Lithothamnion corallioides, growing from 0–8 m (occasionally to 32 m) in the subtidal of quiet bays with clear Atlantic water off the coasts of Spain, France, England, Scotland, and Ireland, and in the Mediterranean. Corallinaceae, for example Lithothamnium corallioides, occur naturally in cold and temperate seas and have been reported in Norway, Canada, Scotland, Ireland, and France.
Primary commercial harvesting of Lithothamnion species is concentrated in North Atlantic maerl beds, with major operations in Ireland, Iceland, and to a lesser extent France. The species is found in just three locations in the world, including the south-west coast of Ireland and Iceland. One major commercial product, Aquamin, is sustainably harvested under licence off the northwest coast of Iceland.
In dietary supplement commerce, Lithothamnion is prepared primarily from the calcareous skeletal remains of the algae. According to Australia's Therapeutic Goods Administration, the substance consists of the skeletal deposits of Lithothamnion spp. (L. corallioides, L. tophiforme) sourced from the Atlantic Ocean, which are washed, dried, and milled. These calcified skeletal remains are harvested, washed, dried, and milled, and provided in a capsule formulation — the capsule form being known as AquaCal in one commercial preparation.
Aquamin is available in various forms such as tablets, capsules, and powders, as well as within foods, low-pH drinks, and sports beverages. The species Lithothamnium calcareum is, besides tricalcium phosphate, often used for food fortification in plant-based milk substitutes to achieve a calcium content comparable to cow's milk.
The use of maerl — the collective term for free-living calcareous coralline algae including Lithothamnion species — has a long history in Western European coastal communities, primarily as an agricultural soil amendment rather than as a human medicinal agent. Maerl has been extracted for centuries mainly for use as an agricultural fertilizer. The amount extracted increased in the late 20th century; in 2000, maerl was extracted at approximately 5,000 tonnes per year in Ireland and approximately 500,000 tonnes per year in France.
Maërl is dredged off the coast of Brittany, at Falmouth in England, in Bantry Bay, Ireland, and in Iceland, dried, ground, and sold as a soil additive, for animal feed supplements, as a water filtration agent, and as a natural anti-osteoporosis remedy. An early reference to maerl was made by John Ray in 1690, who reported it from Falmouth.
Maerl is dredged from the sea floor and crushed to form a powder. It is harvested around the coasts of Brittany in France and Bantry Bay, Ireland, and is a popular fertilizer for organic gardening. In Ireland, use as livestock feed and as a liming agent for acidic soils was widespread. Originally used in Ireland as a natural fertilizer, its effects on livestock health led Lithothamnion calcareum to be investigated for human health applications. Initial anecdotal reports on the algae's benefits for arthritic conditions led to more in-depth studies, and the branded version Aquamin was subsequently developed.
The use of Lithothamnion as a direct human health supplement — particularly for bone strength and joint complaints — is largely a product of the late 20th and early 21st centuries and does not have a documented traditional medicinal role in any formal pharmacopoeial or ethnopharmacological tradition comparable to that of terrestrial medicinal plants. Its historical role was overwhelmingly agricultural.
The primary and defining characteristic of Lithothamnion as a supplement is its exceptional mineral density. The extract contains 12% Ca²⁺, 1% Mg²⁺, and detectable amounts of 72 trace elements, but essentially no organic material. Aquamin is a seaweed-derived mineral source which is rich in calcium, magnesium, and 74 other trace minerals including zinc, iron, and selenium.
The calcium in Lithothamnion is deposited as calcium carbonate within the cell walls of the algae. One of the main features of this alga is the presence of calcium and magnesium carbonate precipitates — calcite crystals — in its cell walls. The algal thallus is made up of successive layers of calcium (and some magnesium) carbonates, which may account for up to 80% of the wet weight.
The structural form of the mineral is considered significant. The different mineral phases of calcium carbonate — calcite, aragonite, and vaterite — exhibit high solubility which makes these minerals bioavailable and bioresorbable. This may be one of the defining factors of plant-based calcium being more bioavailable and better absorbed compared to synthetic forms, which exist in a single crystal structure. The porous, three-dimensional honeycomb microstructure formed by the algal cell wall is also cited as a factor in mineral release kinetics, as calcium and magnesium solubilisation from L. calcareum is highly pH-dependent, and the gastric phase of digestion may improve the release and bioavailability of these minerals.
It is an organic source of Ca²⁺ and magnesium and contains more than 20 trace elements that are bioavailable.
The physiological activity of Lithothamnion is attributed primarily to its multi-mineral matrix and is understood through several proposed mechanisms:
One of the most studied mechanisms involves the interaction of Lithothamnion-derived calcium with parathyroid hormone (PTH). Elevated serum PTH is a driver of bone resorption; calcium supplementation that effectively suppresses PTH can therefore be expected to favor bone retention. Subjects treated with Aquamin F demonstrated a prolonged suppression of serum PTH concentration (significantly lower than placebo at 90, 120, and 240 minutes), while calcium carbonate showed an intermediate response.
Literature has documented that these supplements have the ability to affect osteoblast proliferation and mineralization. The action of Lithothamnion superpositum may be attributable to the presence of other bone-supporting minerals and their effects on alkaline phosphatase, DNA synthesis, and the proliferation and mineralization of osteoblast cells. Furthermore, Lithothamnion calcareum and Lithothamnion superpositum have been observed to directly provide teeth with minerals necessary for remineralization.
In vitro and preclinical evidence suggests that the multi-mineral matrix of Lithothamnion calcareum can influence colonic cell biology through mechanisms beyond calcium alone. The red algae extract was as effective as inorganic Ca²⁺ alone in suppressing growth and inducing differentiation of colon carcinoma cells that are responsive to physiological levels of extracellular Ca²⁺ (1.4 mM). However, with cells that are resistant to Ca²⁺ alone, the extract was still able to reduce proliferation and stimulate differentiation. This suggests that trace minerals beyond calcium contribute to the observed anti-proliferative effect.
The porous algal honeycomb structure is proposed to facilitate mineral release under physiological acidic conditions. Calcium and magnesium solubilisation from L. calcareum is highly pH-dependent, and the gastric phase of digestion may improve the release and bioavailability of these minerals.
Bone health is the most extensively researched area for Lithothamnion supplementation, with evidence spanning in vitro, animal, and human studies, though large-scale human clinical trials with hard endpoints (e.g., fracture reduction) are absent.
Animal studies: A study aimed to determine whether a mineral-rich extract derived from the red marine algae Lithothamnion calcareum could be used as a dietary supplement for prevention of bone mineral loss. Sixty C57BL/6 mice were divided into three groups based on diet: high-fat Western-style diet (HFWD), the same HFWD along with the mineral-rich extract, or a low-fat rodent chow diet (AIN76A). Mice were maintained on the respective diets for 15 months, and long bones were analyzed by three-dimensional micro-computed tomography (micro-CT) and assessed in bone strength studies. Female mice on the HFWD had reduced bone mineralization and reduced bone strength relative to female mice on the low-fat chow diet. The bone defects in female mice on the HFWD were overcome in the presence of the mineral-rich supplement.
Human evidence — calcium metabolism: A double-blind crossover pilot trial tested the hypothesis that botanically derived calcium could demonstrate greater influence over calcium metabolism markers compared with a non-plant-derived calcium carbonate supplement or placebo. Twelve fasting female subjects received a single oral dose of Aquamin F™ (derived from the marine algal Lithothamnion sp.), or calcium carbonate, or placebo. Blood and urine samples were collected at baseline and over 12 hours to evaluate ionized and total calcium and parathyroid hormone (PTH). Subjects treated with Aquamin F demonstrated significantly greater urinary clearance of calcium after 12 hours compared with placebo (P = .004). The study also showed that Aquamin, or Lithothamnion sp., provides prolonged suppression of serum parathyroid hormone (PTH) concentrations following a meal in premenopausal women. Although additional studies are needed, the study suggests Aquamin may represent an effective means of providing calcium supplementation to individuals at risk of bone loss due to osteoporosis.
Bioavailability evidence: A significant benefit reported is enhanced fractional calcium absorption, reported to be 1.57 times higher than calcium carbonate in postmenopausal women, suggesting superior bioavailability. Studies have found that marine-derived calcium has certain advantages over calcium carbonate supplements or other calcium-rich foods; for example, Aquamin has better bioavailability and potential to slow down bone loss compared to calcium carbonate.
Systematic review-level evidence: The overall findings of a review suggest that algae are a promising dietary supplement for promoting bone health in animals and humans. However, this remains a preliminary conclusion given the small sample sizes and short durations of the available human trials.
Evidence strength: Moderate for calcium bioavailability superiority over calcium carbonate in small human trials; preliminary/promising for bone structure endpoints; no long-term fracture-prevention human RCTs published.
Two small randomized controlled pilot trials have examined Lithothamnion-derived Aquamin specifically for osteoarthritis (OA) of the knee.
Trial 1 (Frestedt et al., 2008): This small pilot study evaluated the impact of a natural multi-mineral supplement from seaweed (Aquamin) on walking distance, pain, and joint mobility in subjects with moderate to severe osteoarthritis of the knee. Subjects (n = 70) were randomized to four double-blinded treatments for 12 weeks: (a) glucosamine sulfate (1500 mg/d); (b) Aquamin (2400 mg/d); (c) combined treatment composed of glucosamine sulfate (1500 mg/d) plus Aquamin (2400 mg/d); and (d) placebo. Primary outcome measures were WOMAC scores and 6 Minute Walking Distances (6 MWD). Fifty subjects completed the study and analysis showed significant differences between the groups for changes in WOMAC pain scores over time (p = 0.009 ANCOVA); however, these data must be reviewed with caution since significant differences were found between the groups at baseline for WOMAC pain and stiffness scores. Only the Aquamin and glucosamine groups demonstrated significant improvements in symptoms over the course of the study.
Trial 2 (Frestedt et al., 2009): This small, double-blind, placebo-controlled pilot study investigated the impact of treatment with a natural multi-mineral supplement from seaweed (Aquamin) on 6-minute walking distance (6 MWD), range of motion (ROM), and pain and joint mobility measured by the WOMAC Osteoarthritis Index in subjects with moderate to severe OA of the knee during gradual withdrawal of NSAIDs. Subjects (n = 29) with moderate to severe OA of the knee were randomised to receive either Aquamin (2400 mg/d) or Placebo for up to 12 weeks. The ITT analysis (n = 22) showed no significant differences in WOMAC scores; however, the data did reveal significant improvements in passive and active extension ROM (0.83° ± 1.54 vs. −1.54° ± 2.43; difference, 5.2° ± 2.2, p = 0.028) and 6 MWD (150 ± 48 ft vs. 12.5 ± 31.5 ft; difference, 136 ± 57 ft, p = 0.03) in the Aquamin group compared to the placebo group following a 50% reduction in NSAID use. The treatments were well tolerated and adverse event profiles were not significantly different between the groups. This small preliminary study suggests Aquamin may increase range of motion and walking distances in subjects with OA of the knee and may allow partial withdrawal of NSAIDs over 12 weeks of treatment. Additional research is needed to confirm these preliminary observations.
Evidence strength: Preliminary. Both studies are small-scale pilot trials, funded in part by the ingredient manufacturer, and affected by methodological limitations including baseline imbalances and small sample sizes. Results suggest possible benefit for range of motion and walking distance, but WOMAC composite scores did not reach statistical significance in the second trial. Independent, adequately powered replication is needed.
Lithothamnion calcareum extracts have been tested in vitro and in animal models for potential effects on colon cell biology and polyp formation.
In vitro evidence: A study demonstrated that a mineral-rich material derived from the red algae Lithothamnion calcareum is capable of suppressing the growth of human colon cancer cell lines in vitro. The mineral-rich extract is effective in slowing proliferation and inducing differentiation. Although dietary calcium is an important contributor to health of the colonic mucosa, the degree of Ca²⁺-induced protection against colon cancer can be described as "modest." Some studies, in fact, have failed to demonstrate any statistically significant protection. Identifying additional dietary materials that could be used for colon cancer chemoprevention would have obvious value.
Animal evidence: A study investigated whether a mineral-rich extract derived from the red marine algae Lithothamnion calcareum could be used as a dietary supplement for chemoprevention against colon polyp formation. Some studies have demonstrated the biological effects of Lithothamnion algae, including the inhibition of polyp formation and inflammation in the gastrointestinal tract, and protection against formation of liver tumors in mice fed with a high-fat diet.
Gastroprotective assessment: In a preclinical study evaluating gastric mucosal protection, L. calcareum played no significant role in the protection of the rats' gastric mucosa, nor did it cause an increase in gastric irritation.
Evidence strength: Preliminary (in vitro and animal only). No human clinical trials have been published specifically testing Lithothamnion for colorectal cancer prevention as a primary endpoint. The in vitro findings are exploratory and cannot be extrapolated to human cancer outcomes.
Ryan et al. (2011) provided evidence that the marine-derived multi-mineral Aquamin has anti-inflammatory effects on cortical glial-enriched cultures. Additionally, research using the related species Lithothamnion muelleri has explored anti-inflammatory effects in experimental disease models. One study suggests that treatment with Lithothamnion muelleri extract may be a potential therapy to control inflammatory responses, tissue injuries, and lethality associated with graft-versus-host disease.
Evidence strength: Very preliminary (in vitro and animal models only). No human clinical data are available for inflammatory conditions beyond osteoarthritis.
Clinical trials have used a wide range of daily Aquamin doses, from 800 mg to 2400 mg. Typical Aquamin supplements recommend between 500 mg and 2400 mg daily serving sizes.
Specific dosing guidelines for Lithothamnion calcareum are not yet standardized, as research studies typically employ equivalent calcium doses comparable to those found in conventional calcium supplements.
Aquamin holds U.S. Food and Drug Administration (FDA) Generally Recognized as Safe (GRAS) status, among other certifications. The species Lithothamnium calcareum is also used for food fortification in plant-based milk substitutes. An FDA GRAS notice has been published for seaweed-derived calcium for use in foods in general as a source of dietary calcium. In Australia, the Therapeutic Goods Administration (TGA) recognizes calcified Lithothamnion species as a listed complementary medicine ingredient.
Lithothamnion sp., a red algae of the Corallinaceae family, when harvested in its calcareous form, is rich in calcium, magnesium, and a variety of trace minerals, and is used as a dietary mineral supplement across the world.
Acute toxicity: In an acute toxicity test, Lithothamnion sp. was deemed non-toxic with an LD50 >10 g/kg BW. In an acute toxicity test, mice (n = 20, 10 male, 10 female) were administered a single dose of 10 g/kg BW of Lithothamnion sp. No mortality, or signs of toxicity were observed.
Sub-chronic toxicity and NOAEL: In a standard sub-chronic toxicity study, the no-observed-adverse-effect-level (NOAEL) of Lithothamnion sp. in rats was >2 g/kg BW. In the sub-chronic toxicity arm of a study, SD rats (n = 80, 40 male, 40 female) were randomly divided into four groups and provided pelleted food containing the algae at either 0.00%, 0.625%, 1.25%, or 2.50% inclusion rates for 90 days.
High-dose subchronic toxicity signals: A separate preclinical study using higher doses found concerning signals. In the subchronic toxicity test at high doses, serum levels of albumin, total protein, and calcium decreased, and creatinine levels increased, suggesting hypercalcemia and possible kidney damage associated with liver damage, given that the majority of these parameters were irreversible. This work discussed the relationship of the high concentration of calcium in the product with the observed effects. These findings were observed at supratherapeutic doses (1000–2000 mg/kg in rats) far exceeding human dietary supplementation levels, but they underscore the importance of not exceeding recommended amounts of calcium from combined sources.
Gastric tolerability in clinical trials: The treatments were well tolerated and the adverse event profiles were not significantly different between the groups in the knee osteoarthritis pilot trials using 2400 mg/d of Aquamin for 12 weeks.
Heavy metal contamination risk: Because Lithothamnion species are marine organisms that bioaccumulate minerals from seawater, the potential for trace contamination with heavy metals (such as lead, arsenic, or cadmium) from the surrounding environment is a known quality-control concern for marine-sourced mineral supplements generally. Product quality therefore depends substantially on the sourcing location and manufacturing standards of individual preparations.
Interactions with medications: As a calcium-rich supplement, Lithothamnion preparations share interaction profiles associated with calcium supplementation generally. Calcium can reduce the absorption of certain medications including bisphosphonates, thyroid hormone preparations (levothyroxine), fluoroquinolone and tetracycline antibiotics, and iron supplements when co-administered. These interactions are a class effect of calcium rather than properties specific to Lithothamnion and have not been directly studied for this ingredient in controlled human trials.
Population considerations: Individuals with hypercalcemia, hyperparathyroidism, calcium-containing kidney stones (nephrolithiasis), or renal impairment should exercise particular caution with calcium supplementation from any source, given the preclinical signals observed at high doses. The most pronounced benefits reported in the literature are observed in postmenopausal women and osteoporotic animal models.
Research on this ingredient is evolving, with a growing body of evidence from animal studies and some human trials, including systematic reviews and comparative studies. While the quality of evidence is improving, further large-scale human clinical trials are needed to solidify its efficacy and establish optimal usage guidelines. The majority of human clinical studies to date have been small-scale pilot trials. Several trials have been funded by the ingredient manufacturer (Marigot Ltd.), which introduces potential for industry bias and necessitates independent replication. No Cochrane systematic review specific to Lithothamnion as a dietary supplement had been published at the time of this writing. Hard clinical endpoints — such as incident fracture rates, confirmed radiographic joint space preservation, or incident colorectal cancer rates — have not been tested in registered, adequately powered human RCTs.
Health conditions that Lithothamnion may help support.
Body systems that Lithothamnion may help support.
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