Supplement analysis backed by scientific evidence · PT

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Limited evidenceVitamins & minerals

Cal-Mag-Zinc

The classic three-mineral bone tablet. Calcium has real but modest fracture evidence when paired with vitamin D, while the magnesium and zinc contributions to bone are largely unproven, and the combination as sold has never been trialled.

Evidence last reviewed: August 2026

What the science says

  • Calcium works for fractures mainly alongside vitamin D Moderate evidence

    A 2026 systematic review and meta-analysis in the BMJ found combined calcium and vitamin D supplementation modestly reduced fractures, while either nutrient alone showed little effect. Most cal-mag-zinc products contain no vitamin D.

  • Bone density gains are small and context-dependent Moderate evidence

    A systematic review and meta-analysis in postmenopausal women found calcium and vitamin D combined with exercise produced small improvements in bone mineral density. Supplementation adds little for people already meeting calcium needs through diet.

  • Magnesium and zinc contributions are unproven Limited evidence

    Evidence linking magnesium or zinc supplementation to fracture prevention comes mainly from observational and mechanistic work rather than randomized trials. Their presence in the tablet is not what makes it work.

Dosage & safety

Studied doseTypical products supply 500–1,000 mg calcium, 250–500 mg magnesium and 10–25 mg zinc daily, usually split into two doses since calcium absorption falls above 500 mg at once. Total calcium from food plus supplements should stay around 1,000–1,200 mg/day.
SafetyCalcium supplements can cause constipation and kidney stones, and high intakes have been debated for cardiovascular risk. Magnesium causes loose stools at higher doses and accumulates in kidney impairment. Zinc above 40 mg/day depletes copper. Calcium and zinc both interfere with absorption of thyroid hormone, tetracyclines, quinolones and bisphosphonates — separate by at least four hours for levothyroxine.

Scientific references

Where to buy

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