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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.

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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.

How to take it

TimingSplit it into two doses, since calcium absorption drops off above roughly 500 mg taken at once.
With food?Take it with food — calcium carbonate needs stomach acid to dissolve, and zinc causes nausea without a meal.
Worth knowingCount your dietary calcium first: with dairy in the diet, most people are already near the 1,000–1,200 mg/day target and do not need the supplemental amount on the label.

Interactions

With medications

  • levothyroxine

    Calcium and zinc both bind thyroid hormone in the gut and substantially reduce its absorption. Separate by at least 4 hours

  • tetracycline and quinolone antibiotics

    All three minerals chelate these antibiotics, cutting the absorbed dose. Separate by at least 2 hours, taking the antibiotic first

  • bisphosphonates such as alendronate

    Calcium and magnesium block their already poor absorption almost completely. Take the bisphosphonate on an empty stomach and separate by at least 2 hours

  • thiazide diuretics

    They reduce calcium excretion, so supplemental calcium can push blood calcium too high. Have calcium levels checked if you take both long term

With other supplements

  • iron supplements

    Calcium and zinc both compete with iron for absorption. Take iron at a different time of day

  • copper

    Zinc above 40 mg/day depletes copper. Check the total zinc across all your products stays below 40 mg/day

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does cal-mag-zinc prevent fractures?

Cal-mag-zinc has limited evidence as a combination: calcium modestly reduces fractures mainly when paired with vitamin D (moderate evidence), and most cal-mag-zinc products contain no vitamin D. The magnesium and zinc contributions to bone are unproven, and the tablet as sold has never been trialled.

Do I need a calcium magnesium zinc supplement?

Count your dietary calcium before taking cal-mag-zinc: with dairy in the diet most people are already near the 1,000–1,200 mg/day target. Supplementation adds little bone benefit for people already meeting calcium needs through diet.

When should I take cal-mag-zinc?

Split cal-mag-zinc into two doses with food, since calcium absorption drops off above roughly 500 mg at once, calcium carbonate needs stomach acid, and zinc causes nausea without a meal. Take it at least 4 hours away from levothyroxine.

What are the side effects of cal-mag-zinc?

The calcium in cal-mag-zinc can cause constipation and kidney stones, the magnesium causes loose stools at higher doses, and zinc above 40 mg/day depletes copper. Cal-mag-zinc also blocks absorption of thyroid hormone, tetracyclines, quinolones and bisphosphonates.

Scientific references

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