Should you take copper supplements when you take high doses of zinc?

Zinc and copper compete in the gut for the same absorption pathway. When you take high doses of zinc, the intestinal wall produces more of a protein called metallothionein, a kind of capture molecule that binds copper and prevents it from entering the bloodstream. The result is a lower copper concentration in your blood. This effect is strongest when your copper level is already on the low side to begin with.

A true copper deficiency has noticeable consequences. The most striking are anaemia and a shortage of certain white blood cells that fight infections. This has been documented in people receiving long-term nutrition without copper and in patients who have been taking zinc supplements for an extended period starting from an already low baseline. After roughly three months of zinc supplementation, copper levels can drop to problematically low values.

The relationship works both ways: if you also take copper alongside a high zinc intake, the copper can in turn reduce zinc absorption. They compete with each other in both directions. This means that simply adding a copper supplement is not the obvious solution, as it may disrupt your zinc status.

What this means in practice: if you are taking structurally high doses of zinc, it is sensible to have your copper and zinc blood levels checked, preferably every three months. Supplementation only makes sense if your copper level is actually declining. High blood copper levels are not harmless either: an observational study in older adults found an association between excess copper in the blood and a higher risk of cognitive decline, although that is not proof of direct harm from supplementation.