Most people consume less than the recommended amount of this mineral. Some doctors recommend supplementing the average diet with 1–3 mg of copper per day. While the necessity of supplementing a normal diet with copper has not been proven, most people who take zinc supplements, including the zinc found in multivitamin-mineral supplements, should probably take additional copper.
Cupric oxide (CuO) is a form of copper frequently used in vitamin-mineral supplements sold over-the-counter. However, animal studies have shown conclusively this form of copper is poorly absorbed from the gut; it should therefore not be used in supplements. Several other forms of copper (including copper sulfate, cupric acetate, and alkaline copper carbonate) are better absorbed, and are therefore preferable to cupric oxide.