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Ingredient evidence comparison · non-production preview

Compare ingredient evidence without rankings.

See what each frozen source explicitly supports, where evidence differs, and which questions remain unavailable.

Selected concepts

Two independent ingredient records

Canonical ingredient

Calcium carbonate

mineral compoundNot medically reviewed
Parent supplement
Calcium
Direct source
Calcium
Source revision
June 22, 2026
Open ingredient record

Canonical ingredient

Magnesium oxide

mineral compoundNot medically reviewed
Parent supplement
Magnesium
Direct source
Magnesium
Source revision
January 6, 2026
Open ingredient record
Inspect structural observations
  • The selected ingredients have different parent supplement relationships. This is an identity distinction, not a clinical ranking.
  • Direct evidence for “Identity and what it is” is unavailable for both selected ingredients.
  • Direct evidence for “Common uses” is unavailable for both selected ingredients.
  • Direct evidence for “Biological role” is unavailable for both selected ingredients.
  • Direct evidence for “What evidence has studied” is unavailable for both selected ingredients.
  • Direct evidence for “Potential benefits studied” is unavailable for both selected ingredients.
  • Direct evidence for “Safety considerations” is unavailable for both selected ingredients.
  • Direct evidence for “Side effects” is unavailable for both selected ingredients.
  • Direct evidence for “Medication interactions” is available for Calcium carbonate and unavailable for Magnesium oxide.
  • Direct evidence for “Supplement interactions” is unavailable for both selected ingredients.
  • Direct evidence for “Food interactions” is unavailable for both selected ingredients.
  • Direct evidence for “Intake and dose reference information” is unavailable for both selected ingredients.
  • Direct evidence for “Populations needing caution” is unavailable for both selected ingredients.
  • Direct evidence for “Pregnancy and lactation” is unavailable for both selected ingredients.
  • Direct evidence for “Laboratory and test considerations” is unavailable for both selected ingredients.
  • Direct evidence for “Regulatory status” is unavailable for both selected ingredients.
  • Direct evidence for “Evidence limitations” is unavailable for both selected ingredients.

Aligned evidence topics

Availability stays specific to each ingredient

Identity and what it is

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Common uses

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Biological role

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

What evidence has studied

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Potential benefits studied

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Safety considerations

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Side effects

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Medication interactions

available only for a
Calcium carbonateDirect evidence available

A frozen NIH ODS source explicitly identifies this ingredient or form. Source wording is preserved without creating a new conclusion.

Structural characterization

Evidence profile

No overall rating assigned
Evidence source
NIH ODS evidence synthesis
Linked references
4 identified
Human evidence
Human evidence not identified in the frozen metadata
Randomized trials
Randomized trials not identified in the frozen metadata
Reviews and meta-analyses
Systematic reviews or meta-analyses not identified in the frozen metadata
Evidence recency
1998–2019
Source-described consistency
Not characterized in these source blocks
MEDucated evidence rating
Not assigned

Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

Inspect technical evidence details
Evidence types identified
  • Study type could not be determined3
  • Regulatory source1
Source-described limitations

No explicit limitation phrase was identified in these imported source blocks.

Classified references

  1. Morini E, Catalano A, Lasco A, Morabito N, Benvenga S. L-thyroxine malabsorption due to calcium carbonate impairs blood pressure, total cholesterolemia, and fasting glycemia. Endocrine 2019;64:284-92. [PubMed abstract]

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  2. Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. Jama 2000;283:2822-5. [PubMed abstract]

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  3. Schneyer CR. Calcium carbonate and reduction of levothyroxine efficacy. Jama 1998;279:750. [PubMed abstract]

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  4. U.S. Food and Drug Administration. LEVO-T Label. 2017.

    Regulatory source · Population basis: unknown · Directness: not assessed
Read source wording for Calcium carbonate

Calcium carbonate supplements can interfere with the absorption of levothyroxine (Synthroid, Levoxyl, and others), a thyroid hormone used to treat hypothyroidism and thyroid cancer [104-106]. The FDA-approved label for this medication instructs patients who are taking calcium carbonate supplements to avoid taking levothyroxine within 4 hours of taking the supplement [107].

Where did MEDucated get this?

Calcium

Publisher
NIH Office of Dietary Supplements
Revision
June 22, 2026
Source fingerprint
5139a098b618d4d9810942614ee016aa45b5a58c35e89d7a588a9d7d93a4f2f7
Source blocks
ingredient-block:calcium-carbonate:ods-block:calcium-health-professional:interactions-with-medications:4
Inspect the official source (opens in a new tab)

Source attribution does not imply NIH or ODS endorsement of MEDucated.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Supplement interactions

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Food interactions

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Forms and chemical variants

available for both
Calcium carbonateDirect evidence available

A frozen NIH ODS source explicitly identifies this ingredient or form. Source wording is preserved without creating a new conclusion.

Structural characterization

Evidence profile

No overall rating assigned
Evidence source
NIH ODS evidence synthesis
Linked references
3 identified
Human evidence
Human evidence not identified in the frozen metadata
Randomized trials
Randomized trials not identified in the frozen metadata
Reviews and meta-analyses
Systematic reviews or meta-analyses not identified in the frozen metadata
Evidence recency
2011–2021
Source-described consistency
Not characterized in these source blocks
MEDucated evidence rating
Not assigned

Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

Inspect technical evidence details
Evidence types identified
  • Government reference1
  • Study type could not be determined2
Source-described limitations

No explicit limitation phrase was identified in these imported source blocks.

Classified references

  1. Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press; 2011.

    Government reference · Population basis: unknown · Directness: not assessed

  2. Weaver CM, Heaney RP. Calcium. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:133-49.

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  3. Office of Dietary Supplements, National Institutes of Health. Dietary Supplement Label Database. 2021.

    Study type could not be determined · Population basis: unknown · Directness: not assessed
Read source wording for Calcium carbonate

Many dietary supplements contain calcium, usually in the form of calcium carbonate or calcium citrate. The percentage of calcium that is absorbed from supplements depends on a number of factors, including the form of the calcium and the total amount of elemental calcium consumed at one time.

The two most common forms of calcium in supplements are calcium carbonate and calcium citrate [1]. In people with low levels of stomach acid, the solubility rate of calcium carbonate is lower, which could reduce the absorption of calcium from calcium carbonate supplements unless they are taken with a meal [3]. Calcium citrate is less dependent on stomach acid for absorption than calcium carbonate, so it can be taken without food [1]. In general, however, absorption of calcium supplements is greater when they are taken with food, regardless of whether the user’s gastric acid is low [3]. Other calcium forms in supplements include calcium sulfate, ascorbate, microcrystalline hydroxyapatite, gluconate, lactate, and phosphate [14].

The forms of calcium in supplements contain varying amounts of elemental calcium. For example, calcium carbonate is 40% calcium by weight, whereas calcium citrate is 21% calcium [1]. Elemental calcium is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of calcium supplied by various forms of calcium in supplements.

Some individuals who take calcium supplements might experience gastrointestinal side effects, including gas, bloating, constipation, or a combination of these symptoms. Calcium carbonate appears to cause more of these side effects than calcium citrate, especially in older adults who have lower levels of stomach acid [1]. Symptoms can be alleviated by switching to a supplement containing a different form of calcium, taking smaller calcium doses more often during the day, or taking the supplement with meals.

Where did MEDucated get this?

Calcium

Publisher
NIH Office of Dietary Supplements
Revision
June 22, 2026
Source fingerprint
5139a098b618d4d9810942614ee016aa45b5a58c35e89d7a588a9d7d93a4f2f7
Source blocks
ingredient-block:calcium-carbonate:ods-block:calcium-health-professional:dietary-supplements:1, ingredient-block:calcium-carbonate:ods-block:calcium-health-professional:dietary-supplements:3, ingredient-block:calcium-carbonate:ods-block:calcium-health-professional:dietary-supplements:4, ingredient-block:calcium-carbonate:ods-block:calcium-health-professional:dietary-supplements:6
Inspect the official source (opens in a new tab)

Source attribution does not imply NIH or ODS endorsement of MEDucated.

Magnesium oxideDirect evidence available

A frozen NIH ODS source explicitly identifies this ingredient or form. Source wording is preserved without creating a new conclusion.

Structural characterization

Evidence profile

No overall rating assigned
Evidence source
NIH ODS evidence synthesis
Linked references
8 identified
Human evidence
Human evidence identified
Randomized trials
Randomized trial identified
Reviews and meta-analyses
Systematic reviews or meta-analyses not identified in the frozen metadata
Evidence recency
1990–2012
Source-described consistency
Not characterized in these source blocks
MEDucated evidence rating
Not assigned

Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

Inspect technical evidence details
Evidence types identified
  • Study type could not be determined6
  • Pharmacokinetic study1
  • Randomized controlled trial1
Source-described limitations
  • ODS describes a small study base

    The absorption of magnesium from different kinds of magnesium supplements varies. Forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms [2,12]. Small studies have found that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate [12-16]. One study found that very high doses of zinc from supplements (142 mg/day) can interfere with magnesium absorption and disrupt the magnesium balance in the body [17].

Classified references

  1. Rude RK. Magnesium. In: Coates PM, Betz JM, Blackman MR, Cragg GM, Levine M, Moss J, White JD, eds. Encyclopedia of Dietary Supplements. 2nd ed. New York, NY: Informa Healthcare; 2010:527-37.

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  2. Rude RK. Magnesium. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, Mass: Lippincott Williams & Wilkins; 2012:159-75.

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  3. Ranade VV, Somberg JC. Bioavailability and pharmacokinetics of magnesium after administration of magnesium salts to humans. Am J Ther 2001;8:345-57. [PubMed abstract]

    Pharmacokinetic study · Population basis: human · Directness: not assessed

  4. Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res 2001;14:257-62. [PubMed abstract]

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  5. Mühlbauer B, Schwenk M, Coram WM, Antonin KH, Etienne P, Bieck PR, Douglas FL. Magnesium-L-aspartate-HCl and magnesium-oxide: bioavailability in healthy volunteers. Eur J Clin Pharmacol 1991;40:437-8. [PubMed abstract]

    Study type could not be determined · Population basis: human · Directness: not assessed

  6. Lindberg JS, Zobitz MM, Poindexter JR, Pak CY. Magnesium bioavailability from magnesium citrate and magnesium oxide. J Am Coll Nutr 1990;9:48-55. [PubMed abstract]

    Study type could not be determined · Population basis: unknown · Directness: not assessed

  7. Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomized, double-blind study. Mag Res 2003;16:183-91. [PubMed abstract]

    Randomized controlled trial · Population basis: unknown · Directness: not assessed

  8. Spencer H, Norris C, Williams D. Inhibitory effects of zinc on magnesium balance and magnesium absorption in man. J Am Coll Nutr 1994;13:479-84. [PubMed abstract]

    Study type could not be determined · Population basis: unknown · Directness: not assessed
Read source wording for Magnesium oxide

Supplements can contain a variety of different forms of magnesium, and the absorption of these forms varies. In general, forms of magnesium that dissolve well in liquid have higher absorption than other forms, and the aspartate, citrate, lactate, and chloride forms of magnesium tend to have higher bioavailability than magnesium oxide and magnesium sulfate.

Magnesium supplements are available in a variety of forms, including magnesium oxide, citrate, and chloride [2,3]. The Supplement Facts panel on a dietary supplement label declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound.

The absorption of magnesium from different kinds of magnesium supplements varies. Forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms [2,12]. Small studies have found that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate [12-16]. One study found that very high doses of zinc from supplements (142 mg/day) can interfere with magnesium absorption and disrupt the magnesium balance in the body [17].

Where did MEDucated get this?

Magnesium

Publisher
NIH Office of Dietary Supplements
Revision
January 6, 2026
Source fingerprint
0f84702092574ff8a3b3fe01ab3a977c6a76d37e18b758e3e94b6d3ca55c3d59
Source blocks
ingredient-block:magnesium-oxide:ods-block:magnesium-health-professional:dietary-supplements:1, ingredient-block:magnesium-oxide:ods-block:magnesium-health-professional:dietary-supplements:2, ingredient-block:magnesium-oxide:ods-block:magnesium-health-professional:dietary-supplements:3
Inspect the official source (opens in a new tab)

Source attribution does not imply NIH or ODS endorsement of MEDucated.

Intake and dose reference information

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Populations needing caution

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Pregnancy and lactation

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Laboratory and test considerations

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Regulatory status

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Evidence limitations

unavailable for both
Calcium carbonateEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.

Magnesium oxideEvidence unavailable

Direct source evidence for this ingredient topic is not yet available in MEDucated.

No direct source block is attached to this ingredient topic.