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Calcium is essential for bone mineralization, muscle contraction, nerve transmission, blood clotting, and enzyme function. Bone constantly remodels — osteoblasts build, osteoclasts resorb. After menopause, resorption outpaces formation, leading to osteoporosis. Calcium supplementation + vitamin D slows this imbalance.
Supplemental forms differ:
Chelation — reduces thyroid hormone absorption by up to 60%. Separate by ≥4 HOURS.
Chelation — reduces antibiotic absorption. Separate by ≥2 hours.
Chelation. Separate by ≥2 hours.
Chelation. Separate by ≥2 hours.
Competitive absorption. Separate by ≥2 hours.
Reduce calcium excretion + calcium supplementation → hypercalcemia risk
Hypercalcemia increases digoxin toxicity risk
Competitive absorption at high doses
A 2011 meta-analysis of 11 RCTs found calcium supplements (without co-administered vitamin D) increased myocardial infarction risk by approximately 27% (PMID: 21505219). The proposed mechanism: calcium supplements cause acute spikes in serum calcium that may accelerate vascular calcification. This risk signal is NOT seen with dietary calcium.
Our recommendation: Get calcium primarily from food. If supplementing, keep supplement dose ≤500mg/day, always co-administer vitamin D + K2, and prefer calcium citrate.
Not Prohibited
Tai V et al. Calcium intake and bone mineral density: systematic review and meta-analysis.
Bolland MJ et al. Calcium supplements with or without vitamin D and risk of cardiovascular events.
Heaney RP. Calcium supplementation and incident kidney stone risk.
Burt LA et al. Effect of high-dose vitamin D supplementation on bone density.
Independently graded against 173,636 indexed supplements with 177 published clinical interactions, sourced from PubMed, FDA CAERS, openFDA, and NIH DSLD | Last updated: April 2026
Not medical advice. Based on published clinical research and systematic reviews.
Calcium · interaction landscape
9 flagged
0
Dangerous
6
Moderate
3
Timing
0
Pre-op
Safety
Moderate interactions. Monitoring, timing separation, or dose adjustment may be required.
Levothyroxine (Synthroid)
SourceFDA label
Tetracycline and doxycycline
SourceFDA label
Fluoroquinolones (Cipro)
SourceFDA label
Iron supplements
SourceClinical consensus
Bisphosphonates (Fosamax)
SourceFDA label
Thiazide diuretics (HCTZ)
SourceClinical pharmacology
Timing Separation Rules
Educational information only. This is not medical advice. These statements have not been evaluated by the FDA. Talk to your prescriber before starting, stopping, or combining any supplement with prescription medication.