Home Ingredients AlgaeCal® (Plant-Sourced Calcium — Lithothamnion)

AlgaeCal® (Plant-Sourced Calcium — Lithothamnion)

Lithothamnion superpositum
Evidence Level
Limited
3 Clinical Trials
3 Documented Benefits
2/5 Evidence Score

AlgaeCal® is a calcium supplement made by milling whole, harvested sea algae from the South American coast, which contain calcium together with magnesium and other minerals. The formulas studied added vitamin D3 and vitamin K2. Its human research consists of three open-label studies with no placebo group, all run by the same San Antonio research firm: two shorter studies (6 months and up to 1 year) of bone health plans built around the product, and a 7-year follow-up of 172 women who had already been buying it, which reported bone mineral density rising about 1% a year against an expected decline. Without randomization or a placebo, these gains cannot be credited to the supplement, and both plans in one study also included strontium, which makes bone scans read higher.

Studied Dose 720 to 756 mg/day of algae calcium with vitamin D3 (800 to 1,600 IU), vitamin K2 and 680 mg/day strontium citrate for 6 months in one study; 750 mg/day with 1,000 IU vitamin D3 for 1 year in one plan of another. No study compared doses or used a placebo.
Active Compound Whole-algae calcium from milled sea algae, which the study authors report also contains magnesium, boron, silica, manganese, copper, vanadium and strontium; the studied formulas added vitamin D3 and vitamin K2.

Benefits

Bone mineral density

In a 7-year follow-up of 172 women who had already bought the product for 1 to 7 years, bone mineral density rose about 1.04% a year, against an expected decline of about 0.4% a year from reference databases. Two earlier open-label studies of bone plans built around it (6 months and up to 1 year) also reported gains over expected. None had randomization or a placebo group, so the gains cannot be credited to the supplement.

Supported by Trial 1, Trial 3

Mineral cofactors for bone

The studied formulas paired the algae calcium with vitamin D3 and vitamin K2, and one 6-month plan added extra magnesium; both plans in that study also included strontium citrate. Because each study tested a whole plan, the contribution of the algae calcium is uncertain: it cannot be separated from these added nutrients or from strontium, which by itself makes bone density scans read higher.

Supported by Trial 2

Plant-based and food-form

Made by milling whole harvested algae, it offers an algae-derived alternative to standard calcium salts for people who prefer that source. No published human study has compared its effects with calcium carbonate or citrate; a registered absorption comparison with a calcium carbonate product was completed in 2010 but has no posted results.

Supported by Trial 1, Trial 2

Mechanism of action

1

Bone-forming cells in culture

In a cell study, AlgaeCal raised markers of bone-forming activity (alkaline phosphatase, DNA synthesis) in a cultured human fetal osteoblast cell line more than calcium carbonate or calcium citrate. No human absorption comparison with another calcium source has been published, so better bioavailability is unproven.

2

Vitamin K2 and D3 cofactors

Low vitamin D status reduces calcium absorption, and vitamin K is a cofactor that activates osteocalcin, a main protein in bone. The AlgaeCal studies did not measure osteocalcin, artery calcium or heart outcomes.

Clinical trials

1
Plant Calcium and Bone Density: 7-Year Open-Label Study in Existing Users
PubMed

Open-label, uncontrolled follow-up of customers who had bought AlgaeCal for 1 to 7 years and were offered free repeat scans and blood tests; lead author from Integrative Health Technologies, which ran the earlier company-sponsored AlgaeCal studies. The abstract does not state the funder. Bone density was compared with expected change in 3 reference databases; a separate group of 5,070 people was the comparison for blood chemistry only. (Kaats et al. 2016, J Am Coll Nutr)

172 women with repeat DEXA bone scans and 30 with repeat blood chemistry, all of whom had bought and taken the product for 1 to 7 years.

Bone mineral density rose about 1.04% a year, 7.3% over 7 years, against expected changes of about -0.4% a year in the reference databases. Annual changes in a 45-test blood panel showed no safety signal. With self-selected long-term buyers, no randomization and no placebo group, the change could reflect diet, exercise, other supplements or how the expected-change figure was built.

2
Two Versions of an AlgaeCal Bone Plan: 6-Month Open-Label Study
PubMed

Open-label, sequential (not randomized) comparison with no placebo group, funded by a nutrition company the paper does not name and in part by Integrative Health Technologies, in which the last author holds equity; an independent statistician ran the analyses. Both plans included 680 mg/day strontium citrate, vitamin D3, vitamin K2, and activity and education components. (Michalek et al. 2011, Nutr J)

158 adults on AlgaeCal 1 (125 completed), then a second group of 58 on AlgaeCal 2 (51 completed); mostly women, mean age about 55.

Mean annualized bone mineral density change above expected was 1.15% (AlgaeCal 1) and 2.79% (AlgaeCal 2). Change from baseline was not significant for AlgaeCal 1 (0.48%, p = 0.14) but was for AlgaeCal 2 (2.18%). Strontium deposited in bone makes DXA scans read higher, so part of any gain may be a measurement effect. No clinically significant blood chemistry changes were found.

3
Three AlgaeCal Bone Plans in Women Over 40: Open-Label Comparative Study
PubMed

Open-label, sequential study with no placebo group; for budget reasons the study sponsor compared results with an estimated expected loss of 0.75% a year instead of enrolling a control group. Run by Integrative Health Technologies; the full text identifies the supplement (research code DN0361) as AlgaeCal. (Kaats et al. 2011, Int J Med Sci)

176 women over 40 (of 414 tested); one plan gave 750 mg/day algae calcium with 1,000 IU vitamin D3 for one year, the others added more vitamin D3, other nutrients, and activity and education components.

Women with above-average self-reported adherence had greater bone mineral density increases than the two expected-change reference groups, and the most comprehensive plan did best. Results were split by self-reported adherence, with no placebo comparison. Blood chemistry and quality of life did not change significantly.

Side effects and drug interactions

Common Potential side effects

Mild digestive symptoms such as gas, bloating or constipation can occur with calcium supplements; NIH suggests smaller doses through the day or taking calcium with meals.
Count it toward total calcium from food and supplements; NIH upper limits are 2,500 mg/day for adults 19 to 50 and 2,000 mg/day over 50. Absorption is highest at 500 mg of calcium or less per dose.
If you take a strontium product along with it, tell whoever reads your bone density scans: strontium in bone makes DXA results read higher.
Low bone density needs a clinician's diagnosis and care; this supplement is not a substitute for treatment your clinician recommends.

Important Drug interactions

Levothyroxine (thyroid hormone): calcium carbonate can reduce its absorption, and the drug label says not to take levothyroxine within 4 hours of a calcium carbonate supplement; keep calcium supplements 4 hours apart from it.
Quinolone antibiotics (such as ciprofloxacin): take the antibiotic 2 hours before or 2 hours after calcium. Tetracycline: take calcium 6 hours before or 2 hours after the antibiotic.
Alendronate: take calcium and other supplements at least 30 minutes after the alendronate dose.
Dolutegravir (an HIV medicine): take it 2 hours before or 6 hours after calcium supplements. Lithium: long-term use can raise blood calcium, and calcium supplements could add to that risk.
Iron supplements: calcium may reduce iron absorption, so take calcium and iron supplements at different times of day.
Warfarin: the studied formulas contain vitamin K2, and people taking warfarin need to keep their vitamin K intake steady, so check with the prescriber first.

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Frequently asked questions about AlgaeCal® (Plant-Sourced Calcium — Lithothamnion)

What is AlgaeCal?

AlgaeCal® is a calcium supplement made by milling whole, harvested sea algae from the South American coast, which contain calcium together with magnesium and other minerals. The formulas studied added vitamin D3 and vitamin K2.

What is AlgaeCal used for?

NutraSmarts does not list AlgaeCal under a health category. What the research covers: In a 7-year follow-up of 172 women who had already bought the product for 1 to 7 years, bone mineral density rose about 1.04% a year, against an expected decline of about 0.4% a year from reference databases.

What is the recommended dosage of AlgaeCal?

The clinically studied dose is 720 to 756 mg/day of algae calcium with vitamin D3 (800 to 1,600 IU), vitamin K2 and 680 mg/day strontium citrate for 6 months in one study; 750 mg/day with 1,000 IU vitamin D3 for 1 year in one plan of another. No study compared doses or used a placebo. Always follow the product label and check with a healthcare provider for personal advice.

Is AlgaeCal safe, and does it have side effects?

Side effects and cautions reported for AlgaeCal include: Mild digestive symptoms such as gas, bloating or constipation can occur with calcium supplements; NIH suggests smaller doses through the day or taking calcium with meals. It may also interact with some medications. AlgaeCal is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does AlgaeCal interact with any medications?

Possible interactions include: Levothyroxine (thyroid hormone): calcium carbonate can reduce its absorption, and the drug label says not to take levothyroxine within 4 hours of a calcium carbonate supplement; keep calcium supplements 4 hours apart from it. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for AlgaeCal?

NutraSmarts rates the evidence for AlgaeCal as Limited (2 out of 5). It is backed by 3 study summaries and 11 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(11 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Kaats GR, Preuss HG, Stohs S, Perricone N. A 7-Year Longitudinal Trial of the Safety and Efficacy of a Vitamin/Mineral Enhanced Plant-Sourced Calcium Supplement. J Am Coll Nutr. 2016;35(2):91-9. doi: 10.1080/07315724.2015.1090357.PubMedUsed to support: Open-label, uncontrolled 7-year follow-up of women who had bought AlgaeCal for 1 to 7 years (172 with DEXA scans, 30 with blood chemistry): bone mineral density rose about 1.04% a year (7.3% over 7 years) versus expected changes of about -0.4% a year from 3 databases; no adverse blood chemistry changes versus a 5,070-person comparison group. No randomization or placebo; funder not stated in the abstract.
  2. Michalek JE, Preuss HG, Croft HA, Keith PL, Keith SC, Dapilmoto M, Perricone NV, Leckie RB, Kaats GR. Changes in total body bone mineral density following a common bone health plan with two versions of a unique bone health supplement: a comparative effectiveness research study. Nutr J. 2011;10:32. doi: 10.1186/1475-2891-10-32.PubMedUsed to support: Open-label, sequential 6-month study (no placebo) of two AlgaeCal bone plans in 158 and 58 adults: annualized BMD change above expected was 1.15% and 2.79%; change from baseline was significant only for AlgaeCal 2. Full text: plans supplied 720 to 756 mg algae calcium, vitamin D3, vitamin K2 and 680 mg strontium citrate daily; funded by a nutrition company and in part by Integrative Health Technologies, in which the last author holds equity.
  3. Kaats GR, Preuss HG, Croft HA, Keith SC, Keith PL. A comparative effectiveness study of bone density changes in women over 40 following three bone health plans containing variations of the same novel plant-sourced calcium. Int J Med Sci. 2011;8(3):180-91. doi: 10.7150/ijms.8.180.PubMedUsed to support: Open-label, sequential study of three plant-sourced calcium (AlgaeCal) bone plans in 176 women over 40, compared with estimated expected-change reference groups rather than a control group: women with above-average adherence gained more BMD than expected, and the most comprehensive plan did best; no significant blood chemistry or quality-of-life changes.
  4. Blake GM, Fogelman I. Effect of bone strontium on BMD measurements. J Clin Densitom. 2007;10(1):34-8. doi: 10.1016/j.jocd.2006.10.004.PubMedUsed to support: When some calcium in bone is replaced by strontium, X-ray absorptiometry overestimates bone mineral density because strontium attenuates X-rays more strongly; about a 10% overestimate per 1 molar percent strontium on DXA.
  5. Adluri RS, Zhan L, Bagchi M, Maulik N, Maulik G. Comparative effects of a novel plant-based calcium supplement with two common calcium salts on proliferation and mineralization in human osteoblast cells. Mol Cell Biochem. 2010;340(1-2):73-80. doi: 10.1007/s11010-010-0402-0.PubMedUsed to support: Cell study in cultured human fetal osteoblasts: AlgaeCal increased alkaline phosphatase activity and DNA synthesis more than calcium carbonate or citrate, and calcium deposition versus control. Lab evidence only.
  6. National Institutes of Health, Office of Dietary Supplements. Calcium: Fact Sheet for Health Professionals NIH Office of Dietary Supplements. 2026;Updated June 22, 2026. Accessed October 2026..SourceUsed to support: Not PubMed-indexed (official NIH fact sheet). Absorption from supplements is highest at doses of 500 mg or less; gas, bloating and constipation can occur, eased by smaller doses through the day or taking calcium with meals. Adult upper limits are 2,500 mg/day (ages 19 to 50) and 2,000 mg/day (over 50). High blood calcium is rare in healthy people and usually results from cancer, primary hyperparathyroidism and other conditions. Interactions: dolutegravir (take 2 hours before or 6 hours after calcium), levothyroxine (4 hours apart from calcium carbonate), lithium (added risk of high blood calcium) and quinolone antibiotics (2 hours before or after). Low vitamin D status reduces calcium absorption.
  7. MedlinePlus, US National Library of Medicine. Alendronate: MedlinePlus Drug Information MedlinePlus. 2026;Last revised May 15, 2026. Accessed October 2026..SourceUsed to support: Not PubMed-indexed (NIH consumer drug monograph). Calcium supplements and antacids may interact with alendronate; other medicines, supplements, vitamins or antacids taken by mouth should be taken at least 30 minutes after alendronate.
  8. MedlinePlus, US National Library of Medicine. Tetracycline: MedlinePlus Drug Information MedlinePlus. 2026;Last revised June 15, 2026. Accessed October 2026..SourceUsed to support: Not PubMed-indexed (NIH consumer drug monograph). Antacids and calcium supplements should be taken 6 hours before or 2 hours after tetracycline.
  9. National Institutes of Health, Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals NIH Office of Dietary Supplements. 2025;Updated September 4, 2025. Accessed October 2026..SourceUsed to support: Not PubMed-indexed (official NIH fact sheet). Calcium might interfere with iron absorption, although the effect has not been definitively established, so experts suggest taking calcium and iron supplements at different times of the day.
  10. National Institutes of Health, Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals NIH Office of Dietary Supplements. 2021;Updated March 29, 2021. Accessed October 2026..SourceUsed to support: Not PubMed-indexed (official NIH fact sheet). Vitamin K is a cofactor for the carboxylation of osteocalcin, a main protein in bone. Warfarin antagonizes vitamin K, so people taking it need to keep their vitamin K intake steady.
  11. ClinicalTrials.gov, US National Library of Medicine. The COMparison of CALcium Bioavailability Between AlgaeCal® and a Proprietary Supplement ClinicalTrials.gov. 2026;NCT01609413. Sponsor: Sprim Italia. Completed April 2010; no results posted. Accessed October 2026..SourceUsed to support: Not PubMed-indexed (trial registry record). A randomized, single-blind crossover comparing calcium bioavailability from AlgaeCal and Caltrate 600 (calcium carbonate) in 20 healthy men was registered and is listed as completed in April 2010, with no results posted.