✓ No active regulatory warningsFDA MedWatch, EMA EudraVigilance, WHO VigiBase, WADA Prohibited List · 2026-05-29
📰Read the full Calcium evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ Acute hypocalcemia (perioral tingling, Chvostek/Trousseau signs, QT prolongation) — medical emergency, IV calcium gluconate [3]
⚠ Patient on levothyroxine — calcium must be separated by ≥4 hours to avoid reduced absorption [5]
⚠ Patient on bisphosphonate — calcium chelates the drug if taken together [5]
⚠ Post-thyroidectomy patient with muscle cramps — check ionized calcium urgently [3]
⚠ Pregnant woman in low-calcium-intake population — 1.5–2.0 g/day reduces preeclampsia risk by 55% [8]
🥗 Food first — build your daily 1,000 mg; 1,200 if >50y
Check the foods you regularly eat — the bar fills toward your daily target.
Yogurt, plain (245 g)415 mg
Cheddar cheese (42 g)307 mg
Milk, 2% (240 mL)293 mg
Sardines, canned with bones (85 g)325 mg
Tofu, calcium-set (125 g)253 mg
Kale, cooked (125 mL)94 mg
Fortified orange juice (240 mL)349 mg
White beans, cooked (170 g)81 mg
Check your regular foods above
☑ Risk checker
Low dairy intake (veganism, lactose intolerance without alternatives) [6]
Postmenopausal estrogen deficiency (accelerated bone loss) [1]
Vitamin D deficiency (impairs calcium absorption) [1]
Malabsorptive conditions (celiac disease, inflammatory bowel disease) [1]
Chronic kidney disease (impaired calcitriol production) [3]
Post-gastric bypass surgery [5]
Adolescents with poor dietary habits [6]
Chronic PPI use (reduced calcium carbonate absorption) [5]
Select factors
🔬 Lab interpreter
Recommended test
Serum total calcium (albumin-corrected)
Serum total calcium (albumin-corrected)
Reference range / target
8.5–10.5 mg/dL
8.5–10.5 mg/dL
When to test
If hypoparathyroidism, CKD, or supplementing >1,000 mg/day. Corrected Ca = measured Ca + 0.8 × (4.0 − albumin) [3].
If hypoparathyroidism, CKD, or supplementing >1,000 mg/day. Corrected Ca = measured Ca + 0.8 × (4.0 − albumin) [3].
Serum calcium is tightly regulated and does NOT reflect dietary adequacy. Low serum calcium indicates a serious metabolic disorder, not simply low intake [3].
Full lab monitoring ↓⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
Calcium is the cornerstone of skeletal health but only works in concert with vitamin D and vitamin K. Food sources are preferred over supplements. Calcium carbonate requires acid (take with meals); calcium citrate does not (ideal for PPI users and post-bariatric patients). Never exceed 500 mg per dose [1] [5].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: Specific dosage data under clinical review
👦 Pediatric: See guidance
Infants 0–6 months: 200 mg/day AI; 7–12 months: 260 mg/day. Children 1–3 years: 700 mg/day; 4–8 years: 1,000 mg/day; 9–18 years: 1,300 mg/day [1]. Peak bone mass is achieved by approximately
🏃 Athletes: Standard dose
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Specific dosage data under clinical review
🌱 Vegan: Specific dosage data under clinical review
How to take
🍽 Timing: Calcium carbonate: with meals (requires acid). Calcium citrate: with or without food. Divide doses — do not exceed 500 mg elemental calcium per dose for optimal absorption [1].
💊 With food: Calcium carbonate absorption improves with food. Avoid concurrent high-oxalate foods (spinach, rhubarb) as they bind calcium. Vitamin D enhances intestinal calcium absorption [1].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['Calcium carbonate', 'common', '40% elemental calcium (highest per tablet). Requires gastric acid for absorption — take with meals. Inexpensive and widely available. Most commonly used for supplementation [1].'] | Standard | Check label | |
| ['Calcium citrate', 'preferred', '21% elemental calcium. Does NOT require gastric acid — suitable for patients on PPIs, post-gastric bypass, and elderly with achlorhydria. Better absorbed on an empty stomach [5].'] | Standard | Check label | |
| ['Calcium citrate malate', '', 'Highly bioavailable form used in fortified juices. Good absorption characteristics. Less widely available as standalone supplement [1].'] | Standard | Check label | |
| ['Calcium phosphate', '', 'Contains both calcium and phosphorus. Tricalcium phosphate is 38% elemental calcium. Well tolerated but less commonly used [1].'] | Standard | Check label |
3 Common questions
Should I take calcium supplements or rely on food? ▼
Food sources are preferred when feasible — calcium from food is better absorbed and does not carry the potential cardiovascular concerns associated with supplements [10]. If dietary intake is insufficient (common in lactose intolerance, veganism, or elderly with poor appetite), supplements are appropriate. Aim for food first, supplement the gap [1].
Do calcium supplements cause heart attacks? ▼
This remains debated. Some meta-analyses suggested increased MI risk with calcium supplements (without vitamin D), but the WHI trial and other large studies did not confirm this [10]. Current guidelines from the National Osteoporosis Foundation and ASBMR conclude that calcium intake up to the UL is safe for cardiovascular health. Use food sources preferentially, and supplement only the deficit between dietary intake and RDA [10].
Is calcium carbonate or citrate better? ▼
Calcium carbonate provides more elemental calcium per tablet and is cheaper, but requires stomach acid for absorption — take with meals [5]. Calcium citrate does not require acid and is better for patients on PPIs, post-gastric bypass, or with achlorhydria [5]. Both are effective when used appropriately.
Why should calcium and iron supplements be separated? ▼
Calcium inhibits non-heme iron absorption by up to 50% when taken simultaneously [5]. Take iron supplements at a different meal from calcium supplements. This interaction applies to supplemental calcium, not the modest amounts in a normal mixed meal.
4 Clinical evidence
Strong
Treatment of hypocalcemia (acute and chronic) [3]. Combined calcium and vitamin D supplementation for fracture prevention in elderly populations: the WHI trial (n = 36,282) showed a 29% reduction in hip fracture risk in adherent participants [7]. Essential for bone mineralization — chronic inadequate intake leads to osteoporosis [1]. Calcium supplementation during pregnancy reduces preeclampsia risk: a Cochrane review of 13 trials (n = 15,730) showed 55% reduction in preeclampsia in women with low calcium intake [8]. HIGH
Moderate
Colorectal cancer risk reduction: pooled analysis of prospective studies found 22% risk reduction with highest versus lowest calcium intake [9]. Blood pressure reduction: modest effect (1–2 mmHg systolic) in some meta-analyses, primarily in individuals with low baseline intake [1]. Calcium + vitamin D for prevention of osteoporotic fractures in community-dwelling postmenopausal women [7]. MODERATE
Insufficient
Cardiovascular risk from supplementation: some meta-analyses suggest increased myocardial infarction risk with calcium supplements (without vitamin D), but findings are contested and not confirmed in large randomized trials [10]. Weight management: inconsistent evidence for calcium's role in body weight regulation [1]. Premenstrual syndrome relief: limited trial data [1]. LOW
5 Safety, toxicity & adverse events
Absolute contraindications
✕ Hypercalcemia (serum Ca >10.5 mg/dL)
✕ Severe renal impairment without monitoring
Relative
⚠ History of calcium-containing kidney stones
⚠ Concurrent thiazide diuretics
⚠ Primary hyperparathyroidism
⚠ Sarcoidosis or other granulomatous disease
🚩 Red flags
● Perioral tingling, muscle cramps, and Chvostek/Trousseau signs — acute hypocalcemia, check ionized calcium, give IV calcium gluconate [3]
● QT prolongation on ECG with low calcium — cardiac risk, urgent correction needed [3]
● Patient taking calcium supplements who develops flank pain and hematuria — nephrolithiasis workup [1]
● CKD patient on calcium-based phosphate binders with rising calcium — risk of vascular calcification [3]
● Post-thyroidectomy patient with numbness and tingling within 24–48 hours — check calcium urgently (hungry bone syndrome or hypoparathyroidism) [3]
6 Interactions
Drug interactions
Levothyroxine Major
Mechanism: Calcium forms insoluble complexes with levothyroxine in the GI tract, reducing absorption by up to 50%. [5]
Effect: Elevated TSH, clinical hypothyroidism, need for dose increase. [5]
Action: Separate levothyroxine and calcium by at least 4 hours. Take thyroid medication on an empty stomach in the morning [5].
Bisphosphonates (alendronate, risedronate) Major
Mechanism: Calcium chelates bisphosphonates, preventing absorption (bisphosphonate bioavailability is already only ~1%). [5]
Effect: Abolished bisphosphonate efficacy. [5]
Action: Take bisphosphonate on an empty stomach with plain water. Calcium supplements at least 30 minutes later (for weekly dosing, many experts recommend ≥2 hours separation) [5].
Fluoroquinolone antibiotics (ciprofloxacin, levofloxacin) Major
Mechanism: Divalent cation chelation forms insoluble complexes, reducing antibiotic absorption by 30–50%. [5]
Effect: Subtherapeutic antibiotic levels; treatment failure. [5]
Action: Take fluoroquinolone at least 2 hours before or 6 hours after calcium [5].
Thiazide diuretics (hydrochlorothiazide) Moderate
Mechanism: Thiazides reduce renal calcium excretion. Combined with calcium supplements, may cause hypercalcemia. [3]
Effect: Hypercalcemia: nausea, confusion, polyuria, nephrolithiasis risk. [3]
Action: Monitor serum calcium periodically. Avoid excessive supplementation in patients on thiazides [3].
Iron supplements Moderate
Mechanism: Calcium inhibits non-heme iron absorption at the enterocyte level (competition for DMT-1 transporter). [5]
Effect: Reduced iron absorption by up to 50% when taken simultaneously. [5]
Action: Take iron and calcium at different meals. If both are needed, separate by at least 2 hours [5].
Supplement synergies
Vitamin D · 600–2,000 IU/day
Vitamin D is essential for intestinal calcium absorption. Without adequate vitamin D, only 10–15% of dietary calcium is absorbed versus 30–40% with sufficient vitamin D [1].
Vitamin D is essential for intestinal calcium absorption. Without adequate vitamin D, only 10–15% of dietary calcium is absorbed versus 30–40% with sufficient vitamin D [1].
Vitamin K2 (MK-7) · 100–200 µg/day MK-7
K2 activates osteocalcin (directs calcium to bone) and matrix Gla protein (prevents arterial calcification). The D-K-Ca triad is the foundation of bone health supplementation [4].
K2 activates osteocalcin (directs calcium to bone) and matrix Gla protein (prevents arterial calcification). The D-K-Ca triad is the foundation of bone health supplementation [4].
Magnesium · 320–420 mg/day
Magnesium is required for PTH secretion and vitamin D activation. Magnesium deficiency impairs calcium homeostasis [1].
Magnesium is required for PTH secretion and vitamin D activation. Magnesium deficiency impairs calcium homeostasis [1].
7 Regulatory
United States (FDA): Classified as a dietary supplement and food additive. FDA-authorized health claim: 'adequate calcium and vitamin D as part of a healthful diet, along with physical activity, may reduce the risk of osteoporosis.' UL: 2,000–2,500 mg/day [1].
European Union (EFSA): Authorized health claims for bone and teeth maintenance, muscle function, neurotransmission, blood coagulation, energy metabolism, and digestive enzyme function [11]. UL: 2,500 mg/day [1].
Japan (MHLW): Eligible for Foods with Function Claims. Adequate intake: 650–800 mg/day. Calcium is the most commonly deficient mineral in the Japanese diet.
South Korea (MFDS): Registered health functional food ingredient. Approved claims: bone health and muscle function.
8 US supplement products
7,096
on-market products containing Calcium (NIH DSLD)
Brands carrying Calcium (1071)
Click a brand to see its Calcium products.
9 Frequently paired with
10 Cite this page
Vancouver: Pkhakadze G. Calcium — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Jul 12]. Available from: https://supplement.ge/ingredients/calcium/
APA 7th: Pkhakadze, G. (2026). Calcium — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/calcium/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: January 2027
References: 11 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Calcium — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/calcium/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG