Supplement analysis backed by scientific evidence · PT

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Oyster Shell Calcium

Calcium carbonate ground from oyster shell. Chemically it is the same salt as refined carbonate with no demonstrated advantage, and "natural source" calcium has a documented contamination history.

Evidence last reviewed: August 2026

What the science says

  • Chemically ordinary calcium carbonate Limited evidence

    Oyster shell calcium is calcium carbonate. No human trial has compared it head-to-head with refined calcium carbonate for absorption or for any bone outcome, so the "natural source" premium buys no demonstrated benefit.

  • Calcium supplements barely change fracture risk Strong evidence

    A 2026 systematic review of 69 randomized trials (153,902 participants) found little to no effect of calcium supplementation on any fracture or on falls, with moderate-to-high certainty.

  • Contamination is a real concern Limited evidence

    A review of supplement analyses reported that significant amounts of lead — and aluminium — have been found in calcium carbonate supplements labelled "oyster shell" or "natural source". No in-vivo toxicity was shown, but it is avoidable exposure.

Dosage & safety

Studied dose500–600 mg elemental calcium per dose with food; total intake including diet about 1000–1200 mg/day.
SafetyConstipation, bloating and acid rebound, as with any calcium carbonate. Shellfish-derived, so relevant if you avoid shellfish. Prefer products with published heavy-metal testing, particularly for children and in pregnancy. Blocks absorption of levothyroxine, iron and tetracycline/quinolone antibiotics — separate by four hours.

Scientific references

Where to buy

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