CopperSerum copper
A trace mineral needed for iron transport and connective tissue, balanced against zinc.
Copper is a trace element used by enzymes that handle iron, build connective tissue, produce energy and defend against oxidative damage. Most circulating copper is bound to the protein caeruloplasmin.
It matters partly through its relationship with zinc: the two compete for absorption, so sustained high-dose zinc supplementation can produce copper deficiency, which is one of the few common ways to become deficient.
In practice copper rises with inflammation, pregnancy and oestrogen, because caeruloplasmin does, so the blood level is read with that context and usually alongside caeruloplasmin itself.