Should you take extra copper when taking high doses of zinc?

Zinc and copper compete for the same absorption pathways in the intestinal wall. Taking high doses of zinc blocks the absorption of copper. This is not a theoretical risk: at doses of 100 to 300 mg of zinc per day, anaemia and a deficiency of white blood cells (neutropenia) caused by copper deficiency have been demonstrably established. That is far above the recommended daily amount of 15 mg, but many supplements sold online can quickly end up in a risk zone.

The European Food Safety Authority uses 25 mg per day as a safe upper limit; the US Food and Drug Administration assumes 40 mg per day. If you use zinc above those limits for an extended period, the risk of copper deficiency increases. Even at lower but still excessive doses, there are preliminary indications that the utilisation of copper and iron worsens and that 'good' HDL cholesterol falls. That evidence is less certain, but it does make caution appropriate.

Copper deficiency caused by zinc is often not recognised in practice. Scottish laboratory research showed that in half of confirmed cases the diagnosis had not yet been made. That is concerning, because the consequences can be serious. A severe condition of the spinal cord can develop with prolonged copper deficiency. Anaemia and neutropenia are fortunately fully reversible within four to twelve weeks after copper supplementation, but neurological damage can only be partially reversed.

Practically speaking: if you take more than 25 mg of zinc daily, it is wise to keep an eye on your copper levels. Adding extra copper is not always the solution while large amounts of zinc are still present, because competition in the intestine continues even then. Always discuss prolonged use of high zinc doses with your doctor, so that your blood values (copper, blood count) are checked regularly.