Calcium's Effect on Copper Absorption
900 mg of calcium does not block copper absorption; in fact, calcium supplementation may actually improve copper retention and reduce fecal copper losses. 1
Evidence Contradicts Common Assumptions
The available research directly contradicts the widespread belief that calcium interferes with copper absorption:
Calcium supplementation at doses of 900 mg actually decreased fecal copper losses and improved body copper retention in human studies. 1 This is the opposite of what occurs with iron and zinc, where calcium demonstrably inhibits absorption.
The positive effect of calcium on copper utilization may be mediated through calcium's neutralizing effect on ascorbic acid (vitamin C), which is known to inhibit copper absorption. 1 By reducing the inhibitory effect of ascorbic acid, calcium indirectly enhances copper bioavailability.
Contrast with Other Minerals
Understanding calcium's differential effects on mineral absorption is clinically important:
Calcium doses ≥1000 mg reduce nonheme iron absorption by approximately 50%, and 800 mg calcium reduces heme iron absorption by 37.7%. 2 This effect requires simultaneous presence in the upper small intestine. 3
Calcium supplementation at 468 mg/day significantly reduces zinc absorption and balance by approximately 2 mg/day, and a single 600 mg calcium dose reduces zinc absorption by 50%. 4 High calcium intakes may increase zinc requirements. 4
In contrast, copper absorption is not inhibited by calcium and may actually be enhanced. 1
Clinical Implications
Do not separate calcium and copper supplements - unlike the recommendation for calcium with iron or zinc, there is no need to time copper intake away from calcium. 1
When treating copper deficiency (requiring 4-8 mg copper daily), calcium co-administration is not contraindicated and may theoretically be beneficial if dietary ascorbic acid is high. 5, 1
Magnesium and selenium supplementation, not calcium, are associated with increased fecal copper losses - these minerals warrant more caution when optimizing copper status. 1
Important Caveat
- The beneficial effect of calcium on copper retention was observed in the context of diets with relatively high ascorbic acid content. 1 In diets low in vitamin C, this protective effect may not be as pronounced, though calcium still does not appear to inhibit copper absorption directly.