Copper × Zinc (oral salts: picolinate, citrate, gluconate, oxide, acetate)

Zinc induces metallothionein in the enterocyte, and that protein traps copper and returns it to the gut lumen with the shed cell. NIH ODS puts numbers on it: doses of 50 mg of zinc or more over weeks inhibit copper absorption, reduce immune function and lower HDL cholesterol. The resulting copper deficiency is one of the few supplement interactions with documented neurological harm.

Anaemia unresponsive to iron, neutropenia, and in advanced cases myelopathy: tingling and weakness in the legs, unsteady gait, impaired deep sensation. The neurological picture may not fully reverse once copper is corrected.

Sustained high-dose zinc without oversight is the problem, not zinc itself. Above 40 mg daily long term, monitor the blood count and serum copper. AREDS-type ophthalmic formulas already include copper for this reason, and that is the sensible reference: long-term zinc comes with copper.