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Copper is a metallic trace mineral essential in human nutrition. A versatile mineral involved in numerous biological functions, copper is most concentrated in brain and liver tissues, but significant amounts are also found in muscle, bone, and skin tissues. Over 90% of the body's circulating copper is found in ceruloplasmin, a plasma protein instrumental in iron absorption. Copper is a key component of many vital enzymes, most notably lysyl oxidase (an enzyme involved in the formation of collagen structures) and the antioxidant enzyme superoxide dismutase. Supplemental copper is found in many forms (e.g. sulfate, gluconate, picolinate) and is commonly included in multi-vitamin/mineral formulas.
Copper is found in a wide variety of foods, with the richest sources being oysters and other shellfish. Nuts, legumes, mushrooms, whole grains, and meats are also good sources. Because it is commonly used in plumbing, significant amounts of copper are often present in tap water.
The reference daily intake (RDI) for copper is 2 mg, which most people consume in their regular diet. Vitamin C and zinc interfere with copper absorption, thus people supplementing their diets with these nutrients should also include copper. Because most excess copper is excreted, copper toxicity is rare, occurring mostly in people with Wilson's disease. Copper intake above 10 mg per day may cause nausea. Because it inhibits zinc absorption, copper intake above 3 mg per day is generally not recommended.