Does Calcium Interfere with Copper Absorption?
No, calcium does not interfere with copper absorption. Multiple bariatric surgery guidelines explicitly state that calcium and copper can be supplemented together without concern for interaction, and research confirms calcium does not affect copper balance 1.
Evidence from Clinical Guidelines
The most authoritative evidence comes from bariatric surgery guidelines, where patients require both calcium and copper supplementation and absorption optimization is critical:
The British Obesity and Metabolic Surgery Society (2020) recommends taking iron and calcium supplements 1-2 hours apart to avoid affecting absorption, but makes no such recommendation for calcium and copper 1. This guideline specifically addresses mineral interactions and would have included a calcium-copper separation recommendation if clinically relevant.
The same guideline recommends 2 mg daily copper supplementation alongside 1200-1500 mg calcium daily without any timing separation 1. When discussing the zinc-copper interaction (which is clinically significant), they explicitly state that "zinc and copper have an inverse relationship for absorption" and recommend maintaining specific ratios, but no such warning exists for calcium-copper 1.
The ESPEN Micronutrient Guideline (2022) discusses copper absorption extensively but does not mention calcium as an interfering substance 1. This comprehensive guideline addresses copper deficiency risk factors and absorption issues without identifying calcium as a concern.
The Calcium-Zinc-Copper Relationship
The clinically relevant interaction is between zinc and copper, not calcium and copper:
A ratio of 8-15 mg zinc per 1 mg copper should be maintained to avoid zinc-induced copper deficiency 1. This is why bariatric surgery patients receiving 30 mg zinc daily require monitoring of both zinc and copper levels 1.
Calcium does not share this competitive absorption relationship with copper 1.
Research Evidence Confirms No Interaction
A 1989 human study found that calcium supplements actually improved copper retention rather than inhibiting it 2. The researchers noted that calcium supplementation "depressed fecal copper losses and improved body copper retention," which is the opposite of interference 2.
A 1992 rat study examining mineral interactions found that calcium addition influenced calcium, phosphorus, magnesium, zinc, and iron balances—but not copper 3. This controlled study specifically evaluated whether calcium affected copper and found no effect 3.
Clinical Bottom Line
You can safely recommend calcium and copper supplements together without timing separation 1. The only mineral that requires separation from calcium is iron (1-2 hours apart when absorption optimization is critical, such as post-bariatric surgery) 1, 4. The only mineral that interferes with copper is zinc, which requires ratio monitoring when both are supplemented 1.