Second messenger released from smooth/skeletal ER and mitochondria via ryanodine and IP3 receptors; binds calmodulin to activate downstream kinases/phosphatases and contractile machinery. Active intestinal absorption via TRPV6 is calcitriol-dependent; paracellular absorption dominates at high intakes. Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) is the bone mineral matrix; bone is the dominant body pool.
Half-Life (t½)
PO: 5h
Dosing Guidelines
PO: Typical 667 mg (Range: 500–1000 mg)
Target Organ Systems
digestive
musculoskeletal
Interactions
Magnesium (caution): Shared intestinal transporters at high doses. Separate by 2 h.
Iron (caution): Calcium inhibits non-heme iron absorption. Separate by 2 h.
Iron Bisglycinate (caution): Less affected than ferrous sulfate, but still separate by 2 h.
Levothyroxine (caution): Reduces T4 absorption ~30% — separate by ≥4 h.
Calcitriol (caution): Maximally stimulated Ca²⁺ absorption — risk of hypercalcemia is dose-proportional.
Vitamin D3 (synergistic): D3 drives Ca absorption; their doses should rise together in bone-health stacks.