Copper: Benefits, Dosage, and Safety

What copper is

Copper is an essential mineral naturally present in some foods and available as a dietary supplement. It is a cofactor for several enzymes (cuproenzymes) involved in energy production, iron metabolism, neuropeptide activation, connective tissue synthesis, and neurotransmitter synthesis. One abundant cuproenzyme, ceruloplasmin, carries more than 95% of the total copper in healthy human plasma. Copper is mostly absorbed in the upper small intestine, and almost two-thirds of the body's copper is located in the skeleton and muscle. The average adult has a total body content of 50 to 120 mg copper.

What it does

• Serves as a cofactor for cuproenzymes involved in energy (ATP) production
• Supports iron metabolism, largely through the copper-containing enzyme ceruloplasmin
• Contributes to formation of connective tissue (connective tissue synthesis)
• Supports neurotransmitter synthesis and neuropeptide activation
• Aids defense against oxidative damage through copper-containing superoxide dismutases
• Involved in physiologic processes including brain development, pigmentation, and immune system functioning

How much copper per day

These are population reference values from the NIH and the Dietary Reference Intakes. They are targets for healthy people, not personal prescriptions. The last column is the Tolerable Upper Intake Level, the most you should get from all sources combined.

Deficiency and who is at risk

Copper deficiency is uncommon in humans. Based on studies in animals and humans, its effects include anemia, hypopigmentation, hypercholesterolemia, connective tissue disorders, osteoporosis and other bone defects, abnormal lipid metabolism, ataxia, and increased risk of infection.

Who may need more

• People with celiac disease, who may have copper malabsorption
• People with Menkes disease, who need copper under specialized medical care (subcutaneous copper injections)
• People taking high-dose zinc supplements long term, which can lower copper status
• Most people in the United States meet or exceed the copper RDA through a typical diet and do not need a supplement

Food sources

Richest sources include shellfish (oysters), seeds and nuts, organ meats (beef liver), wheat-bran cereals, whole-grain products, and chocolate. Examples per serving: beef liver (3 oz) 12,400 mcg; cooked oysters (3 oz) 4,850 mcg; unsweetened baking chocolate (1 oz) 938 mcg; potato (1 medium) 675 mcg; shiitake mushrooms (1/2 cup) 650 mcg; dry-roasted cashews (1 oz) 629 mcg.

Forms and absorption

Supplements contain several forms of copper, including cupric oxide, cupric sulfate, copper amino acid chelates, and copper gluconate. To date, no studies have compared the bioavailability of copper from these different forms. Absorption is strongly influenced by dietary copper amount: bioavailability ranges from about 75% when the diet provides only 400 mcg/day down to about 12% when the diet provides 7.5 mg/day. Supplement amounts typically range from a few micrograms to 15 mg (about 17 times the DV).

Safety, excess and interactions

Too much

Chronic exposure to high levels of copper can result in liver damage and gastrointestinal symptoms such as abdominal pain, cramps, nausea, diarrhea, and vomiting. Copper toxicity is rare in healthy individuals without a hereditary copper homeostasis defect, but has been reported from drinking water containing high copper levels leached from copper pipes and fixtures. People with Wilson's disease (a rare autosomal recessive ATP7B mutation with defective copper clearance) have a high risk of copper toxicity, which can cause neurologic and liver damage, cirrhosis, acute hepatitis, hemolytic crisis, and liver failure. The FNB set the ULs based on levels associated with liver damage; the ULs do not apply to people receiving supplemental copper under medical supervision.

Interactions to know

• Zinc (nutrient interaction): high dietary or supplemental zinc interferes with copper absorption; moderately high zinc intakes of about 60 mg/day for up to 10 weeks reduced erythrocyte copper-zinc superoxide dismutase, a copper status marker, and excessive zinc use can cause copper deficiency
• Medications: per ODS, copper is not known to have any clinically relevant interactions with medications

How status is measured

Copper status is not routinely assessed in clinical practice, and no biomarkers accurately and reliably assess copper status. Studies typically measure copper and cuproenzyme activity in plasma and blood cells (serum copper and ceruloplasmin), since people with known deficiency often have low levels; however, plasma ceruloplasmin and copper can be influenced by estrogen status, pregnancy, infection, inflammation, and some cancers. Normal serum concentrations are 10 to 25 mcmol/L (63.5 to 158.9 mcg/dL) for copper and 180 to 400 mg/L for ceruloplasmin.

Regulated as a dietary supplement ingredient under DSHEA, not as a drug; the FDA does not evaluate supplements for effectiveness before marketing. The FDA Daily Value (DV) for copper is 0.9 mg (900 mcg) for adults and children age 4 and older. FDA does not require food labels to list copper content unless copper has been added to the food.

What the evidence supports

We grade the strength of evidence behind each common reason people take copper, mirroring how the NIH describes it.