Copper

Copper is a chemical element that, in trace amounts, is indispensable to nearly all living things, including humans ^[2]. In the body it works mainly as a cofactor, a helper built into the structure of certain enzymes that cannot function without it; these copper-dependent enzymes carry out a range of essential jobs ^[1][4]. They include cytochrome c oxidase, which sits at the end of the chain that generates cellular energy; a form of superoxide dismutase that neutralises damaging free radicals; ceruloplasmin, which is needed to move iron around the body; lysyl oxidase, which cross-links the collagen and elastin that give strength to connective tissue; dopamine beta-hydroxylase, which helps make the neurotransmitter noradrenaline; and tyrosinase, which produces the pigment melanin ^[1].

Copper is supplied by the diet, with particularly rich sources including liver and other organ meats, shellfish such as oysters, nuts, seeds, whole grains, legumes, mushrooms and chocolate ^[1]. It is absorbed in the small intestine and carried in the blood largely bound to ceruloplasmin, and the body maintains a fairly constant total copper content by adjusting how much it absorbs and by excreting the excess in bile ^[1][5]. This tight regulation exists because free copper is chemically reactive and can generate harmful oxygen radicals, so the metal is kept bound to proteins and its transport is closely controlled ^[4][5]. Recommended intakes for adults are on the order of about a milligram a day, with an upper limit set well above that to guard against toxicity ^[1].

Copper deficiency, though less familiar than iron or vitamin shortfalls, has clear consequences ^[3]. Because copper is needed to use iron and to make blood cells, a deficiency can produce anaemia and a fall in white blood cells, and because copper enzymes support the nervous system it can also cause a spinal cord and nerve disorder known as myeloneuropathy ^[3]. Deficiency is uncommon on a normal diet but can arise from conditions that impair absorption, from weight-loss surgery on the stomach, from long-term intravenous feeding, and notably from taking too much zinc, which interferes with copper uptake in the gut ^[1][3]. Blood-related problems generally reverse with copper replacement, whereas nerve damage may only partly recover ^[3].

At the other end of the range, an excess of copper is toxic ^[2][4]. Swallowing large amounts of copper salts causes stomach upset and can damage the liver and red blood cells, and chronic overload harms the liver through oxidative stress ^[2][4]. Two inherited disorders illustrate the importance of copper balance: in Wilson's disease a faulty copper-exporting protein lets copper build up to poisonous levels in the liver and brain, while in Menkes disease a different transporter defect prevents copper from being absorbed and distributed, causing a severe deficiency with brittle hair and neurological damage ^[1][4]. Researchers have also described a specific copper-triggered form of cell death, termed cuproptosis, which is now being studied in relation to disease ^[5].

As a nutrient, copper is available in multivitamin and mineral products and as standalone supplements in forms such as copper gluconate, sulfate or citrate, which are better absorbed than cupric oxide ^[1]. Supplementation is mainly relevant for people at risk of deficiency, such as those with malabsorption or on high-dose zinc, rather than for the general population, since most people obtain enough from food ^[1][3]. Because the safe range is narrow, routine high-dose copper supplements are generally unnecessary and can themselves cause harm ^[1][2].

Copper has a narrow useful range; the tolerable upper limit for adults is around 10 mg per day. Excess causes nausea, vomiting, liver damage, and in severe cases neurological harm. People with Wilson's disease must avoid supplemental copper entirely. For most people, food provides enough and extra isn't needed.

Zinc is the interaction that causes real harm. Sustained high dose zinc induces metallothionein in the intestinal lining, and metallothionein binds copper more tightly than zinc, trapping it in cells that are then shed into the gut. The result is copper deficiency presenting as anemia, neutropenia and sometimes an irreversible myelopathy, and cases have followed both long term zinc supplements and zinc containing denture adhesives.

Copper is a divalent cation, so it chelates tetracycline and fluoroquinolone antibiotics in the gut and reduces the absorption of both; the effect depends on the two being taken close together. High dose ascorbic acid and molybdenum compounds lower copper absorption by other routes, and tetrathiomolybdate is used deliberately for that purpose.

Absorption also depends on gastric acid, so proton pump inhibitors and gastric surgery reduce it. The chelators used in Wilson disease, penicillamine and trientine, work by stripping copper out of the body, and supplemental copper works directly against them.

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