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Calcium (Dietary & Supplemental)
Builds and maintains bone density while supporting muscle contraction, nerve signaling, and cardiovascular function.
What the evidence says
Calcium doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1967–2026 with a typical study size of 11,005 participants.
Based on 564 studies · 90 meta-analyses · 407 RCTs · 160,372 total participants
Confidence
High confidenceBy outcome
The 2025 Cochrane review of 10 trials and 37,504 participants finds calcium makes little to no difference to pre-eclampsia (RR 0.83, 95% CI 0.67-1.04). For bone, calcium plus vitamin D slowed bone loss and cut fractures by 12% in the 2007 Lancet pooling of 63,897 people (RR 0.88), but a 2023 pooling of 18 trials found no significant fracture reduction at any site, and a 2023 Cochrane review found no bone density benefit in premenopausal women. Against that sits a replicated cardiovascular harm signal: myocardial infarction HR 1.31 (2010 BMJ) and cardiovascular disease RR 1.15 with no heterogeneity (2021). Blood pressure falls by about 1.9 mmHg. Deficiency matters, but supplementation has a contested benefit and a measured harm.
461 randomised trials
every one checked individually
Every randomised or controlled trial of Calcium indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Jul 2026
971 trials ongoing or recruiting · NaN completed on ClinicalTrials.gov
856 of the completed trials have posted results
Registered trials show research momentum for Calcium, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Calcium meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Authorised claims
“Calcium contributes to normal blood clotting”
“Calcium contributes to normal energy-yielding metabolism”
“Calcium contributes to normal muscle function”
“Calcium contributes to normal neurotransmission”
“Calcium contributes to the normal function of digestive enzymes”
“Calcium has a role in the process of cell division and specialisation”
“Calcium is needed for the maintenance of normal bones”
“Calcium is needed for the maintenance of normal teeth”
Not authorised by EFSA
“Calcium helps to keep a healthy blood pressure”
“Calcium contributes to normal functioning of cells”
“omega 3 pourrait améliorer la fixation du calcium sur l'os”
“Mineralwasser/ Calcium [In german:] kräftigt die Nägel Clarification provided strengthens the nails”
“Calcium helps manage your weight Calcium contributes to weight control. Calcium modulates energy metabolism”
“Calcium Diet which includes several daily servings of low-fat milk products (about 1200 mg of calcium/day) helps to control blood pressure”
“Calcium phosphoryl oligosaccharide remineralizes/restores tooth enamel after meals increases tooth surface hardness helps strengthen teeth”
“Calcium [In german : ] Calcium ist wichtig zur Unterstützung des Stoffwechsels Clarification provided Calcium supports the regulation of the acid base balance”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Calcium is the most abundant mineral in the human body, with approximately 99% stored in bones and teeth, and the remaining 1% circulating in blood and soft tissues where it plays critical roles in muscle contraction, nerve transmission, hormone secretion, and blood clotting.
Dietary calcium intake is often inadequate, particularly in older adults, postmenopausal women, and individuals following plant-based diets.
Supplemental calcium, particularly when combined with vitamin D3, slows bone loss and may modestly reduce fracture risk, while the current Cochrane review finds little to no difference in pre-eclampsia.
However, some studies suggest high-dose supplementation may carry cardiovascular risks, which is a reason to dose carefully and to count calcium from food as well as supplements.
Calcium carbonate and calcium citrate are the most commonly used supplemental forms, with bioavailability differing based on gastric acidity and food intake timing.
Calcium is the primary structural mineral incorporated into hydroxyapatite crystals that give bone its strength and rigidity.
Blood calcium levels tightly regulate parathyroid hormone (PTH), which in turn controls bone resorption and kidney calcium reabsorption.
Intracellular calcium is the key trigger for actin-myosin crossbridge formation in muscle fibers and neurotransmitter release at synapses.
Calcium modulates vascular smooth muscle contraction and endothelial function, influencing blood pressure regulation.
Calcium and vitamin D co-supplementation has been shown to reduce circulating inflammatory biomarkers.
How Calcium works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
1200mg/day recommended; calcium + vitamin D3 combination is standard of care for osteoporosis prevention. Discuss cardiovascular risk with physician.
High-dose calcium (1.5-2g/day) is recommended for preeclampsia prevention in low-intake populations. Standard RDA is 1000mg/day in pregnancy.
1200mg/day with vitamin D3. Prefer calcium citrate due to reduced gastric acid. Monitor for hypercalcemia and kidney function.
Use with extreme caution. Risk of calcium accumulation, vascular calcification, and adynamic bone disease. Requires medical supervision.
Calcium intake is often lower in plant-based diets; supplementation or calcium-fortified foods are frequently recommended. Calcium citrate preferred due to lower oxalate interference.
Calcium needs are high during growth (1300mg/day for ages 9-18). Dietary sources preferred; supplementation only if dietary intake is inadequate.
Use calcium citrate, which does not require stomach acid for absorption. PPIs reduce absorption of calcium carbonate.
Avoid supplemental calcium — these conditions can cause hypercalcemia due to aberrant vitamin D activation. Medical supervision required.
Calcium and other minerals can reduce the absorption of a bisphosphonate taken by mouth. Follow the instructions for the exact medicine and formulation, and ask your pharmacist when to take calcium. Oral alendronate must be taken with plain water at least 30 minutes before food, other drinks or medicines; other formulations have different instructions. This absorption and spacing instruction does not apply to a bisphosphonate given by injection or infusion. A grade for this interaction is held for clinical review and has not been validated, so no severity is given. The precaution still applies: ask a pharmacist about the exact supplement and medicine. Do not stop or change prescribed medicines based on this notice.
Calcium can bind levothyroxine in the gut and reduce absorption. Follow the exact levothyroxine product’s timing and order; the US Synthroid label specifies at least four hours before or after calcium. A grade for this interaction is held for clinical review and has not been validated, so no severity is given. The precaution still applies: ask a pharmacist about the exact supplement and medicine. Do not stop or change prescribed medicines based on this notice.
Calcium chelates tetracyclines and reduces their absorption. Ask the pharmacist to schedule calcium apart from the antibiotic, following that antibiotic's label.
Calcium can reduce the absorption of some fluoroquinolones taken by mouth, but the effect and any required interval depend on the exact antibiotic and product. Ask your pharmacist whether separation is needed and follow that medicine’s label. This gut-absorption interaction does not apply to an antibiotic given into a vein. A grade for this interaction is held for clinical review and has not been validated, so no severity is given. The precaution still applies: ask a pharmacist about the exact supplement and medicine. Do not stop or change prescribed medicines based on this notice.
Calcium lowers non-heme iron absorption from a dose taken at the same time. When treating iron deficiency, take them at different times of day.
Thiazide diuretics increase calcium reabsorption in kidneys, potentially causing hypercalcemia when combined with supplements. Monitor serum calcium. A grade for this interaction is held for clinical review and has not been validated, so no severity is given. The precaution still applies: ask a pharmacist about the exact supplement and medicine. Do not stop or change prescribed medicines based on this notice.
Loop diuretics increase urinary calcium excretion, potentially increasing calcium requirements.
Long-term corticosteroid use decreases intestinal calcium absorption and increases urinary excretion. Higher calcium intake may be needed.
High blood calcium can increase susceptibility to digoxin toxicity. Avoid excessive supplementation and have calcium and renal function assessed when indicated.
Chronic use increases vitamin D catabolism, reducing calcium absorption. Increased calcium and vitamin D may be needed.
Tip: Switch to calcium citrate, increase water and fiber intake, split doses
Tip: Take with meals, switch from carbonate to citrate form
Tip: Take with food, reduce dose temporarily
Tip: Maintain adequate hydration, avoid excess doses, dietary calcium preferred over supplements
Tip: Do not exceed 2500mg/day total calcium; monitor blood levels in high-risk populations
Tip: Avoid doses exceeding 2500mg/day, especially with antacids
Calcium has an evidence score of 5.5/10 — moderate evidence based on 565 indexed studies, including 7 meta-analyses. Builds and maintains bone density while supporting muscle contraction, nerve signaling, and cardiovascular function. Representative study: PMID 41330480.
The commonly studied dose of Calcium is 1000–1200mg daily (split doses) (no cited trial states the dose it used). Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Calcium is in split doses through the day. Take it with food. Calcium absorption is most efficient in doses of 500mg or less at a time.
Calcium has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. The most commonly reported side effects are constipation, bloating and gas, nausea. Use caution if any of these apply to you: Hypercalcemia (elevated blood calcium) — calcium supplementation is absolutely contraindicated; Hypercalciuria (elevated urinary calcium excretion) without medical supervision; Primary hyperparathyroidism without medical supervision.
Vitamin D3
Probably helpsHormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
Zinc
Likely helpsInvolved in 300+ enzymatic reactions — supports immune defense, testosterone production, wound healing, and sleep quality.
Omega-3
Probably helpsEssential fatty acids critical for brain health, mood regulation, and reducing inflammation throughout the body.
CoQ10
Likely helpsA lipid-soluble antioxidant central to mitochondrial energy production, with the strongest trial support for fertility/IVF outcomes and heart failure.
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Reviewed by Dr. Baher Al Hakim · Last reviewed October 2026 · evidence from 566 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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