Copper is an essential mineral found naturally in some foods. It is a cofactor for several enzymes involved in energy production, iron metabolism, neuropeptide activation, connective tissue synthesis, and neurotransmitter synthesis. Ceruloplasmin, a coenzyme abundant in the body and involved in iron metabolism, carries more than 95% of the total copper in healthy human plasma. Copper is also involved in many physiological processes, including angiogenesis; neurohormone homeostasis; regulation of gene expression; brain development; pigmentation; and immune system functioning. In addition, defense against oxidative damage depends on copper-containing superoxide dismutases. Copper deficiency is rare in humans. Effects of copper deficiency include anemia, hypopigmentation, hypercholesterolemia, connective tissue disorders, osteoporosis and other bone defects, abnormal lipid metabolism, ataxia, and increased risk of infection.