Mesophyllum

Mesophyllum superpositum: A Comprehensive Reference on the Marine Coralline Alga Used in Dietary Supplements

1. Identity: Botanical Classification, Nomenclature, and Natural Source

1.1 Taxonomic Classification

Mesophyllum superpositum is a marine red alga whose taxonomy has been subject to ongoing revision. The organism's original name was Lithothamnion superpositum, first described by Foslie in 1900, and it was subsequently transferred to the genus Mesophyllum by W.H. Adey in 1970. Health Canada's Natural Health Product Ingredients Database recognizes it under the family Hapalidiaceae, genus Mesophyllum, species superpositum, with the principal taxonomic synonym Lithothamnion superpositum.

As of a 2023 revision published in the Journal of Phycology, Mesophyllum superpositum is now also regarded as a synonym of Roseolithon superpositum (Foslie) P.W. Gabrielson, Maneveldt, Hughey & V. Peña, following taxonomic contributions that redefined Lithothamnion and introduced new genera within Hapalidiales. Consequently, the commercial supplement literature employs the name Mesophyllum superpositum, while cutting-edge phycological taxonomy has reassigned the species to Roseolithon superpositum, and earlier supplement and dental research literature also uses Lithothamnion superpositum interchangeably.

The formal phycological classification accepted by AlgaeBase as of 2026 is: Kingdom Plantae, Phylum Rhodophyta, Class Florideophyceae, Subclass Corallinophycidae, Order Hapalidiales, Family Hapalidiaceae, Genus Lithothamnion (with the species now re-placed as a synonym of Roseolithon superpositum).

In supplement literature, Mesophyllum superpositum is described as a species of red coralline algae found off the South American coast, placed in the Rhodophyta phylum, order Corallinales, and belonging to the Mesophyllum genus, one of over 100 species within that genus.

1.2 Broader Context within Coralline Algae

Coralline algae are red algae in the order Corallinales, characterized by a thallus containing calcareous deposits within their cell walls that impart hardness. Their colors are typically pink or another shade of red, though some species can be purple, yellow, blue, white, or gray-green. They typically grow in a crustose manner, encrusting rocks and other hard substrates in the intertidal zone of rocky shorelines and within coral reefs.

Rhodoliths — free-living structures composed mostly of nongeniculate coralline red algae — include Mesophyllum as one of the common nongeniculate rhodolith-forming genera alongside Hydrolithon, Neogoniolithon, Lithophyllum, Sporolithon, Lithothamnion, Phymatolithon, and Spongites.

1.3 Geographic Distribution and Harvesting

In the dietary supplement context, Mesophyllum superpositum is described as a naturally occurring marine alga harvested from beaches in South America. AlgaeCal, the primary commercial product based on this alga, is a plant-sourced form of calcium made by milling whole, live-harvested sea algae found on the South American coastline. Some commercial descriptions indicate Atlantic Ocean harvesting, while others specify South American coastlines; both characterizations appear in the published literature and product documentation.

1.4 Physical Characteristics and Mineral Structure

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. These structures are comprised of calcium, magnesium, and other trace minerals, which the algae extract from the sea and deposit in their cell walls, forming a hard, chalky crust that can exist in various forms, such as free-living, branched, encrusting, or nodding.

1.5 Common Names and Commercial Identity

In the dietary supplement trade, Mesophyllum superpositum is most widely encountered under the trademarked ingredient name AlgaeCal. It is also sometimes referred to as algas calcareas (Spanish for calcareous algae) or simply "red coralline algae." The related genus Lithothamnion (notably L. calcareum and L. corallioides), sold under brand names such as Aquamin, represents a close relative that is frequently used interchangeably in the broader "calcified seaweed" supplement category.

1.6 Common Forms and Preparations

In commercial supplement formulations, Mesophyllum superpositum is prepared by milling the whole, live-harvested dried algae into a powder, which is then encapsulated or blended into multi-ingredient bone-health formulas. A representative commercial product (AlgaeCal Plus) provides, per daily serving of four capsules: calcium (from AlgaeCal® Mesophyllum superpositum) 720 mg, magnesium (from AlgaeCal® Mesophyllum superpositum plus magnesium oxide) 350 mg, trace minerals (from AlgaeCal® Mesophyllum superpositum) 1,464 mg, vitamin D3 (cholecalciferol) 1,600 IU, vitamin K2 (as MK-7) 100 mcg, boron (glycinate) 3 mg, and vitamin C (calcium ascorbate) 50 mg.

2. Historical and Traditional Use

2.1 Coralline Algae in Ancient and Pre-Modern Medicine

The first coralline alga recognized as a living organism was probably Corallina, noted in the 1st century AD. In 1837, Rodolfo Amando Philippi recognized that coralline algae were not animals, and he proposed the two generic names Lithophyllum and Lithothamnion.

The earliest recorded medicinal use of corallines involved the preparation of a vermifuge (antiparasitic remedy) from ground geniculate corallines of the genera Corallina and Jania, a practice that stopped towards the end of the 18th century.

2.2 Maerl and Coralline Algae in European Coastal Traditions

Related coralline algae species, collectively known as maerl, have a documented history of use in coastal European communities. Maerl (Lithothamnion calcareum), a coralline seaweed, has a long history of use in agriculture, and is currently also promoted as a natural source of calcium for human consumption in the form of supplements and food additives, and in cosmetics. Maerl 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.

While the genus Mesophyllum itself is not associated with documented pre-modern traditional use in pharmaceutical or ethnobotanical records, the broader family of calcareous red algae (Hapalidiaceae) has been used in coastal folk medicine traditions. Red algae have been used as a traditional medicine for centuries. Red algae are also a traditional part of oriental cuisine.

It is important to note that no primary ethnobotanical or pharmacopeial sources document a specific traditional use of Mesophyllum superpositum as a distinct species — its identity as a supplement ingredient is essentially a modern commercial development. There is no established record of pre-20th-century indigenous or traditional cultures using this particular species medicinally in a documented, systematic way distinct from related coralline algae.

3. Key Constituents and Active Compounds

3.1 Macrominerals

The alga is naturally high in calcium and contains all 13 bone-supporting minerals, making it a high-mineral food. Besides calcium, the alga contains magnesium, potassium, boron, copper, manganese, silicon, strontium, nickel, phosphorus, selenium, vanadium, and zinc.

Minerals extracted from the algae include approximately 12% calcium, 1% magnesium, and 72 additional trace minerals documented as essential for bone health. The principal structural mineral in the cell walls is high-magnesium calcite (a form of calcium carbonate). High Mg-calcite is the most soluble form of calcium carbonate. This solubility characteristic is proposed — though not conclusively demonstrated through independent clinical pharmacokinetics — to contribute to higher bioavailability compared with geological calcium carbonate.

3.2 Mineral Profile from Published Research

The supplement is made by milling whole, live-harvested sea algae found on the South American coastline, and in addition to calcium, the algae contains other naturally occurring minerals in the following rank-order of percentage: carbon, chloride, magnesium, manganese, selenium, silicon, sodium, strontium, titanium, vanadium, boron, silica, and copper — many of which have been reported to play a role in bone health.

3.3 Proposed Mechanisms of Action

The hypothesized mechanisms by which Mesophyllum superpositum (and related coralline algae) may support bone mineral density include:

• Multi-mineral matrix delivery: The plant-cellular matrix of the algae is proposed to deliver calcium and co-minerals in a biologically accessible form. 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.
• Osteoblast stimulation: An in vitro study compared AlgaeCal with the two top-selling conventional calcium salts. Cultured human osteoblast cells (hFOB 1.19) were treated with AlgaeCal, calcium carbonate, or calcium citrate, in a study that demonstrated superiority over the two most commonly used calcium salts. The study results showed that AlgaeCal increased alkaline phosphatase activity — a marker of osteoblast differentiation and bone-forming activity — in human osteoblast cell culture compared to the conventional calcium sources. This is an in vitro finding only.
• Remineralization: It was observed that Lithothamnion superpositum directly provides teeth with minerals necessary for remineralization (calcium, magnesium, phosphorus, etc.), suggesting it could be used as an effective natural alternative for tooth remineralization.
• Co-nutrient synergy: When formulated with vitamin D3, vitamin K2, and strontium citrate (as in the commercially studied AlgaeCal Plus preparation), the combined supplement is thought to act through multiple pathways: vitamin D3 facilitates intestinal calcium absorption, vitamin K2 directs calcium into bone matrix, and the multimineral algal base supplies the raw materials for hydroxyapatite crystal formation.

It must be emphasized that the specific mechanism by which the algal matrix itself — as opposed to the co-formulated vitamins and minerals — uniquely promotes bone density has not been definitively isolated in well-controlled human pharmacological studies. The mechanisms described above are supported primarily by in vitro data or are inferred from the known functions of the constituent minerals.

4. Scientific Evidence by Area of Use

4.1 Bone Mineral Density (BMD) and Bone Health

This is the primary and most-studied application of Mesophyllum superpositum-derived supplements. The clinical evidence base consists of three published human studies, all centered on the commercial preparation AlgaeCal (AC) — a multi-ingredient supplement rather than the isolated algal powder alone.

Study 1: Comparative Effectiveness Research Study (Nutrition Journal, 2011)

After signing an informed consent, 158 adults agreed to follow an open-label bone-health plan for six months after taking a DXA test of bone density, a 43-chemistry blood test panel and a quality of life inventory (AlgaeCal 1). Two weeks after the last subject completed, a second group of 58 was enrolled and followed the identical plan, but with a different bone-health supplement (AlgaeCal 2).

Both groups experienced a significant positive mean annualized percent change (MAPC) in BMD compared to expectation — AlgaeCal 1: 1.15%, p = 0.001; AlgaeCal 2: 2.79%, p = 0.001. Both groups experienced a positive MAPC compared to baseline, but only AlgaeCal 2 experienced a significant change from baseline (AlgaeCal 1: 0.48%, p = 0.14; AlgaeCal 2: 2.18%, p < 0.001). The MAPC in AlgaeCal 2 was significantly greater than that in AlgaeCal 1 (p = 0.005).

Increased compliance was associated with greater increases in BMD in both groups. No adverse effects were reported in either group. The study was registered at ClinicalTrials.gov (NCT01114685).

Limitations: The study was funded by a small nutritional company with a limited budget that initially sought to examine the safety and efficacy of a bone-health plan using an open-label protocol under "real world" conditions approximating those in which consumers were likely to follow either plan. Notwithstanding the absence of an RCT, these findings warrant further study in view of the unusual increases in BMD in both study groups. The open-label, non-placebo-controlled design is a fundamental methodological limitation.

Study 2: Comparative Effectiveness Study in Women Over 40 (International Journal of Medical Sciences, 2011)

Three groups of post-menopausal women each took different AlgaeCal formulations, with all groups increasing bone density at one year. The smallest average increase among the three groups was 1.3% — an extraordinary result since traditional calcium supplements do not increase bone density. This comparative effectiveness study measured bone density via DEXA scan at baseline and then again at six months and one year.

Limitations: This study also lacked a placebo-controlled randomized design. Results represent changes in bone density measured relative to age-expected rates of decline rather than against an equivalent untreated control group receiving only a placebo.

Study 3: 7-Year Longitudinal Trial (Journal of the American College of Nutrition, 2016)

The objective of this study was to examine the safety and efficacy of vitamin-mineral enhanced plant-sourced calcium AlgaeCal calcium (AC) in female consumers who had taken the supplement from 1 to 7 years. Consumers who had completed at least one dual-energy x-ray absorptiometry (DEXA) bone mineral density (BMD) scan (N = 172) and/or blood chemistry test (N = 30) and purchased AC from 1 to 7 years were contacted and offered complimentary repeat tests. Safety and efficacy were examined by annualized changes in a 45-measurement blood chemistry panel and changes in BMD.

Results showed no adverse effects or safety concerns in any of the annualized within-group changes in the 45 blood chemistries, or in between-group changes in a similar control group (n = 5,070) who completed the same measurements. Consistent and statistically significant within-group increases were found for the 7-year study period and when compared to expected BMD.

Results of this 7-year study showed that AC produced consistent and linear gains in BMD, averaging 1.04% per year over the full duration of the study. In addition to calcium and vitamin D3, the AC supplements provided trace minerals, magnesium, vitamin K (as MK-7), boron, vitamin C, and elemental strontium (from citrate).

Critical Appraisal of the Bone Health Evidence

The weight of clinical evidence for Mesophyllum superpositum-based supplements is notable in that it demonstrates positive BMD outcomes, but the evidence base carries several methodological limitations that restrict the strength of conclusions:

• Almost all of the research on AlgaeCal is industry funded, so there are clear conflicts of interest. To give credit to the researchers, however, they did disclose their conflicts of interest.
• There is almost no independent research on AlgaeCal. It is important to separate the effects of AlgaeCal the ingredient from AlgaeCal the supplement, since ingredients like vitamin D and vitamin K improve bone density by themselves without any calcium. How much of the effect on bone density is due to AlgaeCal the ingredient and how much is due to the inclusion of other vitamins and minerals remains unclear.
• None of the three published human studies were randomized placebo-controlled trials (RCTs), which is the gold standard for establishing supplement efficacy. The absence of a true control arm makes it impossible to attribute BMD changes definitively to the AlgaeCal ingredient rather than to co-formulated vitamins, strontium citrate, lifestyle changes, or regression to the mean.
• All studies were open-label, meaning neither participants nor researchers were blinded to the treatment assignment, introducing risk of performance and detection bias.
• No independent, head-to-head, placebo-controlled RCT of the isolated Mesophyllum superpositum powder has been published in the peer-reviewed literature as of the date of this article.

4.2 Tooth Remineralization

An in vitro comparative study investigated the remineralization potential of Lithothamnion superpositum (the same organism under an earlier name) in human tooth enamel. The study found that Lithothamnion calcareum and Lithothamnion superpositum directly provided the tooth with minerals necessary for remineralization (calcium, magnesium, phosphorus, etc.) and hence could be used as an effective natural alternative for tooth remineralization. The p-value was 0.001 between the commercial remineralizing agents (CPP-ACPF) and the alternative calcium sources. Limitations of the study include unknown cytotoxic effects of algae, insufficient studies to determine the optimum concentration and pH of the solution, and the need for further in vitro and in vivo tests comparing the algae to various other remineralizing agents. This evidence is preliminary and limited to in vitro conditions only.

4.3 Osteoarthritis and Joint Health

Research in the broader "calcified seaweed" supplement category — including the Aquamin product derived from related Lithothamnion species — has examined joint health outcomes. A natural seaweed-derived mineral supplement for knee osteoarthritis was studied in a randomized, placebo-controlled pilot trial published in Nutrition Journal in 2009 (PMID: 18279523; PMCID: PMC2265739). However, this study used Aquamin (derived from Lithothamnion species, not Mesophyllum superpositum), and no equivalent joint-health trial specifically using Mesophyllum superpositum could be identified in the peer-reviewed literature. These results, therefore, cannot be directly attributed to Mesophyllum superpositum.

4.4 Animal and Pre-Clinical Evidence

Calcium extracted from marine algae was found to show a beneficial anabolic effect on bone skeletal calcification in animal models of osteoporosis. These results support the biological plausibility of the mineral delivery mechanism but cannot be directly extrapolated to human clinical outcomes.

5. Body Systems and Health Areas

Based on verifiable evidence in the available literature, Mesophyllum superpositum is associated with the following body systems and health areas:

• Skeletal system / bone health: The primary and best-evidenced application. The alga's calcium, magnesium, and trace mineral content are associated with bone mineral density maintenance and, in industry-funded open-label studies, with BMD increases in peri- and post-menopausal women and older adults.
• Dental health: Preliminary in vitro evidence suggests remineralization potential for tooth enamel through calcium and phosphorus deposition.
• Musculoskeletal system: By proxy of its mineral content, the supplement is used in the context of osteoporosis prevention and management, though no direct fracture-reduction data are available for Mesophyllum superpositum specifically.

6. Dosage Forms and Dosages Reported in Studies

The following dosage information is derived directly from the published clinical literature and product documentation; no inferences are made:

• The commercial AlgaeCal Plus product provides per daily serving of four capsules: calcium (from AlgaeCal® Mesophyllum superpositum) 720 mg, magnesium 350 mg, trace minerals 1,464 mg, vitamin D3 1,600 IU, vitamin K2 (as MK-7) 100 mcg, boron (glycinate) 3 mg, and vitamin C (calcium ascorbate) 50 mg.
• As a dietary supplement, the recommended dosing is four capsules daily, taken as two capsules twice a day with meals.
• When used alongside the companion product Strontium Boost, which provides strontium 680 mg (as natural strontium citrate) per two-capsule daily serving, strontium should be taken at least two hours apart from calcium supplements or calcium-rich meals to ensure best absorption.
• In the toxicological safety study, daily administration of AC by oral gavage at dose levels of 0, 500, 2,500, and 5,000 mg/kg/day during gestation days 5–19 appeared to result in no adverse toxicological effects to the pregnant rat or its developing offspring.

7. Safety Considerations and Interactions

7.1 Toxicological Safety Profile

A dedicated safety evaluation examined a novel plant-based calcium supplement derived from marine algae and containing high levels of calcium, magnesium, and other bone-supporting minerals (commercially known as AlgaeCal). The study evaluated broad-spectrum safety using a variety of toxicological assays including acute oral, acute dermal, primary skin irritation, and primary eye irritation toxicity.

Under the conditions of the study, the acute oral LD50 of AC was found to be greater than 5,000 mg/kg body weight in rats, while the single acute dermal LD50 was greater than 2,000 mg/kg body weight. The primary skin irritation index was found to be 0.4 and classified as slightly irritating to the skin.

The results from the current study demonstrated a broad-spectrum safety profile for AC, and no significant toxicities were observed in the toxicity models used.

In the 7-year longitudinal human study: No adverse effects or safety concerns were found in any of the annualized within-group changes in the 45 blood chemistries or in between-group changes in a similar control group (n = 5,070) who completed the same measurements.

7.2 Heavy Metal and Contaminant Considerations

Marine algae, particularly those harvested from coastal environments, can accumulate heavy metals from the surrounding seawater. The commercial product undergoes third-party testing to ensure its purity and safety, including checks for heavy metals and microbial activity. Independent verification of heavy metal levels in commercially marketed Mesophyllum superpositum products has not been published in the peer-reviewed literature identified in preparation of this article. The absence of published independent contaminant screening data is a recognized gap in the evidence base.

Regarding the cytotoxic effects of algae-derived calcium in dental applications, researchers noted that the cytotoxic effects of algae are unknown, and there are not enough studies to determine the optimum concentration and pH of the solution.

7.3 Drug and Supplement Interactions

Because Mesophyllum superpositum-based supplements deliver pharmacologically relevant amounts of calcium, magnesium, and (in combination formulas) vitamin K2, the following interactions are documented in product literature with plausible pharmacological basis:

• Some medications and supplements require separation from AlgaeCal Plus to limit potential interactions. For example, thyroid medication, antacids, and certain antibiotics should be taken at least four hours from AlgaeCal Plus.
• Iron supplements should also be separated correctly. A standalone iron supplement should be taken two hours from AlgaeCal Plus to avoid decreased absorption; if iron comes from a multivitamin, separation is not required.
• Vitamin K2, including the vitamin K2 in AlgaeCal Plus, may interfere with certain anticoagulant drugs and should be avoided unless otherwise directed.

7.4 Long-Term Safety — Evidence Gaps

With little independent research on AlgaeCal, and of the research that exists being largely industry-funded, there is no well-characterized independent data on the potential side effects of AlgaeCal. Regular calcium supplements (such as calcium carbonate and calcium citrate) are linked to both heart problems and kidney damage. Whether the same risks apply to AlgaeCal is unknown; conventional calcium supplement data is all that is currently available for comparison until long-term, independent research is conducted on isolated AlgaeCal as an ingredient.

7.5 Taxonomic Uncertainty and Product Labeling

A notable complication in interpreting the safety and efficacy literature is the taxonomic instability of the organism. As described above, the same organism has appeared in the published literature as Lithothamnion superpositum, Mesophyllum superpositum, and (as of 2023) Roseolithon superpositum. Furthermore, some commercial review sources describe AlgaeCal as derived specifically from the marine alga Lithothamnium superpositum — a spelling variant further complicating literature searches and product identification. Researchers and consumers relying on any single nomenclature may miss relevant cross-referenced evidence.

8. Evidence Strength Summary

• Bone mineral density (human, clinical): Three published open-label, industry-funded, non-placebo-controlled studies demonstrating positive BMD trends in peri/post-menopausal women and older adults. Results are consistent but methodologically weak due to lack of blinding, randomization, and placebo controls, and difficulty in isolating the contribution of the algal ingredient from co-formulated nutrients. Evidence is preliminary to moderate in weight; independent replication with RCT design is lacking.
• Osteoblast effects (in vitro): Preliminary; single cell-culture study showing favorable effects on alkaline phosphatase activity, proliferation, and mineralization compared to conventional calcium salts. Cannot be directly extrapolated to human outcomes.
• Tooth remineralization (in vitro): Single in vitro study showing comparable or superior remineralization versus CPP-ACPF reference. Extremely preliminary; no human clinical data available.
• Animal data: Consistent with plausible bone-anabolic effects; cannot be extrapolated to human clinical benefit.
• Toxicological safety: Preclinical toxicology profile is broadly reassuring; 7-year longitudinal blood chemistry data in humans showed no safety signals, though this was industry-funded and not placebo-controlled.

References

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