Key Takeaways (expand)
- Copper is a trace element required by all living organisms.
- This mineral serves as a component of approximately two dozen proteins and enzymes (called cuproenzymes), making a variety of physiological functions copper-dependent!
- Some of the most important of these functions are connective tissue maturation, bone formation, energy production, iron homeostasis, neurotransmission, and melanin formation.
- Copper also helps scavenge free radicals and facilitate redox reactions, giving it an antioxidant role.
- Copper helps regulate gene expression through its involvement in RNA production and in regulating oxidative stress within cells (which helps activate signal transduction pathways).
- Although elevated blood levels of copper have been associated with a higher risk of cardiovascular disease, there’s little evidence that dietary copper is harmful for the heart; blood levels can rise substantially due to non-dietary factors (including physical stressors like inflammation and disease).
- Copper may be involved in the body’s innate immune response to bacterial infection: it exhibits direct toxicity to pathogens (through its ability to produce hydroxyl radicals), and can also disrupt bacterial protein structures.
- Some limited evidence suggests copper can promote bone health and protect against osteoporosis, possibly via the copper-dependent enzyme lysyl oxidase (which supports collage in the bone matrix); but, more research here is needed!
- Copper may also play a role in cancer progression, particularly angiogenesis (the development of new blood vessels that allow tumors to grow).
- Copper deficiency is fairly uncommon, but when it occurs, can lead to abnormally low levels of neutrophils (a type of white blood cell), anemia that doesn’t respond to iron therapy, impaired growth, neurological symptoms, and loss of pigmentation on the body; copper deficiency during pregnancy can increase the risk of low birth weight and neurological problems in newborns.
- Excess copper can be hazardous, too: chronically high intake can increase the risk of liver injury, and may alter immune function and antioxidant status.
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Copper is a trace element needed by all living things—plant, animal, and microorganism alike! It was first determined to be essential in 1928, when an experiment showed that rats couldn’t produce sufficient red blood cells when they were fed a copper-deficient diet; the issue was corrected when their diet was supplemented with copper-containing ash. But, copper’s medical history goes back much further than that: as early as 400 BCE, Hippocrates was prescribing copper compounds to help treat diseases, and even the Ancient Egyptians were aware of its sterilizing effects (for example, the Edwin Smith Papyrus dating back to the 17th century BCE mentions using copper to sterilize drinking water and chest wounds). In fact, up until the modern era of antibiotics, copper was variously inhaled as a powder, ingested, or applied externally as a way to treat infectious conditions!
The name “copper” derives from the Greek island of Cyprus (the Greek name of which is Kupros), where copper mines date back to the fourth millennium BCE, when Cypriots first fashioned tools from copper.
Copper is a component of a number of important enzymes and proteins, and is needed for the proper development, growth, and maintenance of the brain, heart, bone, connective tissue, and other organs in the body. It’s also involved in cholesterol and glucose metabolism, helps regulate iron levels, and is needed for red blood cell formation.
Excellent sources of copper include oysters and other shellfish, legumes, nuts, seeds, organ meat, sweet potatoes, salmon, tempeh, dark chocolate, avocados, and mushrooms.
The Biological Roles of Copper
In the body, copper exists in the cuprous (Cu1+) or cupric (Cu2+) forms, and serves as a component of about two dozen proteins and enzymes (called cuproenzymes). As a result, a number of physiological functions in the body are copper dependent—including connective tissue maturation, bone production, energy production, neurotransmission, iron homeostasis, and melanin formation! For example, the copper-containing enzyme lysyl oxidase is needed to form cross-links in collagen and elastin (important components of connective tissue), as well as to maintain the health of connective tissue in the blood vessels and heart; it also plays a role in bone formation. Another copper-dependent enzyme, cytochrome c oxidase, catalyzes the reduction of molecular oxygen to water—in turn generating an electrical gradient that mitochondria use to create adenosine triphosphate, or ATP (the energy currency of cells). Cytochrome c oxidase is also involved in synthesizing phospholipids used for the myelin sheath (the protective membrane around nerve cells), while the enzyme dopamine beta-hydroxylase helps convert the neurotransmitter dopamine to another neurotransmitter, norepinephrine—making copper important for nervous system health and functioning. The protein ceruloplasmin helps regulate iron levels in the central nervous system. And, the copper-containing enzyme tyrosinase is needed for the production of melanin, which helps pigment the skin, eyes, and hair.
Copper also plays a major role in scavenging free radicals and facilitating oxidation-reduction (redox) reactions, largely due to its ability to easily donate and accept electrons. It serves as a component of two forms of superoxide dismutase (a very important enzyme group!), which functions as an antioxidant by helping convert free radicals to hydrogen peroxide. These copper-containing forms are the copper/zinc superoxide dismutase found in most cells (including red blood cells), and extracellular superoxide dismutase, which is found in high concentrations in the lungs. Copper-containing ceruloplasmin can also function as an antioxidant through two avenues: one, by binding free copper ions and preventing them from causing oxidative damage, and two, by helping load iron onto transferrin, in turn preventing free iron ions from participating in reactions that generate free radicals.
Another role of copper is in regulating gene expression. This mineral is necessary for the production of RNA, and copper can increase the amount of oxidative stress within cells (which then activates a variety of signal transduction pathways, leading to increased expression of genes involved in detoxifying reactive oxygen species).
Copper is plays a particularly important role in growth and development in early life. During the third trimester of pregnancy, the fetus rapidly accumulates copper in its liver, and by birth, has about four times the copper concentration of an adult! These liver copper stores are then used to supply copper to the rest of the body during the infant’s growth, since human breast milk is relatively low in copper. Interestingly, infants have unique biochemical mechanisms for regulating their copper status during this phase of life; over time, more permanent mechanisms develop.
Copper is likewise required by the immune system to support the production of some cytokines by T cells and regulate T cell proliferation (cell division), and dietary copper is important in resistance to infection.
The body tightly regulates copper homeostasis, and has complex mechanisms to help eliminate excess copper when it builds up, or retain copper when dietary intake is more scarce. When dietary copper intake is low, the body depletes copper stores in the liver to be used elsewhere; when too much copper builds up, the liver excretes it through bile. However, chronic over-ingestion or under-ingestion of copper can disrupt this homeostasis and lead to issues of excess or deficiency!
Interactions with Other Nutrients
Copper has some important relationships with other nutrients—one of the most significant being iron. Adequate copper status is needed for the body to properly metabolize iron, and inadequate copper can disrupt iron homeostasis. Four different copper-containing enzymes (called multi-copper oxidases, or ferroxidases) are involved in oxidizing ferrous iron to its ferric form, which can then be transported by the iron-carrying protein transferrin to the site of red blood cell formation. These ferroxidases include circulating and membrane-bound ceruloplasmin, which represent the vast majority of plasma copper; Zyklopen, which is found in the placenta; and Hephaestin, which is found in the intestine. In addition, copper-deficient animals have been shown to accumulate iron in their livers, due to copper being necessary for transporting iron out of this organ. Human studies, too, have demonstrated that copper deficiency can cause ceruloplasmin deficiency, in turn leading to iron overload or scarring in the liver. Conversely, ingesting high levels of iron has been shown to reduce the absorption of copper, especially in infants. So, these nutrients need to be kept in balance with each other for optimal health!
Copper also interacts with zinc in some noteworthy ways. Ongoing zinc supplementation of 50 mg daily or higher has been shown to induce copper deficiency—likely due to increased synthesis of a protein called metallothionein, which blocks the absorption of certain metals (including zinc!) by binding them and trapping them in intestinal cells. However, copper doesn’t appear to affect zinc status in any similar way.
Some limited research also suggests that high-dose vitamin C supplementation could impair the oxidase activity of copper-dependent ceruloplasmin. One study found that supplementing with 1.5 g daily of vitamin C, for a period of two months, led to a significant drop in ceruloplasmin oxidase activity; another study found that three weeks of supplementing with 605 mg of vitamin C daily likewise decreased ceruloplasmin oxidase activity. Interestingly, copper status remained unaffected during these studies, suggesting the effects of vitamin C on copper and its enzymes warrant further research!
Meanwhile, copper absorption appears to be enhanced when it’s ingested alongside animal protein, phosphate, or citrate.
Copper in Health and Disease
Copper serves as a component of numerous enzymes and proteins in the body, giving it diverse roles in the growth, development, and maintenance of various organs (including the heart and brain), bone, and connective tissue. Copper is also involved in glucose and cholesterol metabolism, helps regulate gene expression, can scavenge free radicals, and is needed for the production of red blood cells.
Copper and Cardiovascular Disease
Copper has been studied for its role in cardiovascular health and disease, although the results of this research aren’t always straightforward. In vitro experiments show that free copper and ceruloplasmin can promote LDL oxidation (a contributor to atherosclerotic plaque buildup), making some researchers hypothesize that copper could contribute to cardiovascular disease. But, what happens inside test tubes isn’t always the same as what happens inside of a living body, and very little evidence exists that copper plays a significant pro-oxidant role in the human cardiovascular system. In fact, because it serves as a component of several enzymes with antioxidant properties (such as superoxide dismutase), some researchers even believe copper may help protect against cardiovascular disease!
Human research has been similarly hard to assess. In observational studies, higher blood copper levels have been associated with a higher risk of cardiovascular disease incidence and mortality, as well as with poorer short-term outcomes among people with chronic heart failure or ischemic heart disease. And, a large prospective cohort study of middle-aged men found that high blood levels of copper were associated with a 50% greater risk of all-cause, cardiovascular, and cancer mortality. However, blood copper levels aren’t always a reflection of nutritional intake: they’re essentially a measurement of serum ceruloplasmin, which can fluctuate dramatically depending on a variety of non-dietary factors (for example, its levels can increase by over 50% in response to physical stressors such as disease, inflammation, and trauma—regardless of how much copper is being consumed!). So, higher blood copper levels are sometimes a marker for inflammation-related increases in ceruloplasmin, rather than a high intake from the diet.
In human intervention studies, the results of altering dietary copper levels have likewise been mixed. Some very small studies have shown that reduced copper consumption adversely impacts blood lipids, including raising total and LDL cholesterol while decreasing HDL cholesterol. But, most other studies of this nature have failed to show any effect of copper on blood lipids, including trials of copper supplementation of 2 to 3 mg daily. Similarly, in placebo-controlled trials, copper supplementation of up to 6 mg daily didn’t increase the participants’ LDL susceptibility to oxidation, and actually decreased the susceptibility of their red blood cells to oxidation—supporting the idea that copper’s pro-oxidant properties in vitro don’t happen the same way in our bodies!
Copper and Immune Health
Some evidence shows that copper may be involved in the innate immune response to bacterial infection. Copper exhibits direct toxicity through its ability to produce hydroxyl radicals—which can directly damage the lipids, nucleic acids, and proteins in invading pathogens. Copper can also disrupt protein structures by either binding to amino acids or interacting with polypeptide backbones. As a result of these properties, the body can use copper as a weapon against infection: activated macrophages, for example, accumulate copper in their phagosomes to help destroy microbes! Interestingly, some bacteria express copper tolerance genes that allow them to survive in the presence of copper (such as copper-exporting ATPases and other copper detoxification defenses), making them more resistant to attack from the body’s immune system.
Copper and Bone Health
Research (albeit limited!) suggests that copper could play a supportive role in bone health and protecting against osteoporosis. Some small studies have shown that reduced copper intake leads to increased breakdown of bone tissue—which, long-term, would be expected to cause a decrease in bone mineral density. However, other studies have found that copper supplementation of up to 6 mg daily had no effect on markers of bone breakdown or bone formation. Likewise, some research has shown that elderly patients with hip fractures have significantly lower levels of serum copper compared to matched controls, and one small study found that copper supplementation helped slow the loss of bone mineral density from the lumbar spine; but, other research has found no differences in serum copper levels among women with or without osteoporosis, and larger controlled studies have shown that supplemental copper was less effective than other mineral supplements (particularly calcium) in slowing the loss of bone mineral density. Theoretically, copper could help support bone health due to the activity of the copper-dependent enzyme lysyl oxidase, which supports healthy collagen (an important component in bone matrix!). Overall, it’s difficult to draw conclusions about the real-world effects of dietary copper on bone health with the evidence we currently have available, and more research is needed on this topic!
Copper and Cancer
There’s some evidence that cancer could play a role in cancer progression—especially angiogenesis, or the development of new blood vessels (which enables tumors to grow, invade, and metastasize). A copper-chelating agent called tetrathiomolybdate has been used to test the effects of copper depletion on tumor growth for a number of cancers (including liver cancer, colorectal cancer, breast cancer, kidney cancer, mesothelioma, and squamous cell carcinoma), with studies generally showing that lowering copper levels indeed reduces tumor angiogenesis. However, most of this research has been done in animals or in vitro, with only a handful of pilot studies in humans.
Health Effects of Copper Deficiency
True copper deficiency is relatively uncommon, although in extreme cases, blood levels of copper and ceruloplasmin levels can drop to only 30% of normal values and manifest with clinical symptoms. When severe, copper deficiency can cause anemia that doesn’t respond to iron therapy, as well as abnormally low counts of neutrophils (a type of white blood cell)—which in turn can increase a person’s susceptibility to infection. Similarly, people with copper deficiency and/or genetic conditions that lead to low copper levels have been shown to produce monocytes with impaired responses to immune challenges. Some evidence also suggests that copper insufficiency could reduce the body’s ability to regulate blood cell renewal in general. Less frequently, copper deficiency can cause neurological symptoms, impaired growth, and the loss of pigmentation on the body (due to copper’s role in melanin formation).
During pregnancy and early childhood, copper deficiency can be particularly damaging. Maternal copper deficiency has been linked to low birth weight, as well as to muscle weakness and neurological problems in the newborn. And, copper deficiency in infants and young children can sometimes lead to abnormal bone development and osteoporosis.
People at the greatest risk of copper deficiency include infants and children fed only cow’s milk formula (which is relatively low in copper), infants with chronic diarrhea, people recovering from malnutrition, diabetics, patients with cystic fibrosis, people with malabsorption syndromes such as celiac disease or short bowel syndrome, and people with excessive zinc intake. Iron supplementation can also increase the risk of copper deficiency.
Importantly, low blood copper (technically known as hypocupremia) can result from not only inadequate dietary intake, but also from genetic disorders of copper metabolism, such as aceruloplasminemia (which involves the abnormal accumulation of iron in internal organs) and Wilson’s disease (which causes excess copper to accumulate in the vital organs, but paradoxically can decrease its concentration in the blood!). Similarly, mutations in the ATP7A gene lead to impaired transport of copper within cells, leading to systemic copper deficiency and a decline in copper-dependent enzyme activity—ultimately culminating in a condition called Menkes disease. Along with neurological symptoms (including intractable seizures), Menkes disease can feature connective tissue problems, hair abnormalities, and hemorrhage.
Problems From Too Much Copper
Although most health experts agree that too little copper is a bigger public health issue than too much copper, copper toxicity can occur from either acute or chronic excess. Consuming extremely high amounts of copper in one sitting (upwards of 20 to 70 g, usually in the form of copper salts) has led to reports of abdominal pain, nausea and vomiting, headache, diarrhea, tachycardia, dizziness, respiratory difficulty, gastrointestinal bleeding, bloody urine, liver failure, kidney failure, and even death. Consuming water with high copper levels (typically 3 to 6 mg/L) can likewise lead to gastrointestinal upset, nausea, and vomiting.
Meanwhile, long-term high copper intake (30 to 60 mg daily for years) can increase the risk of liver injury, and may impact some markers of immune function and antioxidant status. Intakes of up to 10 mg daily are generally considered the safe upper limit for this nutrient, except in people with genetic disorders impacting copper metabolism.
How Much Copper Do We Need?
The recommended dietary allowance (RDA) for copper is 900 ug daily for adults in general, 1000 ug daily while pregnant, and 1300 ug daily while breastfeeding. Due to nutrient interactions, people supplementing with zinc or iron may need to consume more copper to compensate for its reduced bioavailability (especially during pregnancy!). Meanwhile, different health organizations have set tolerable upper intake levels for copper at 5 to 10 mg daily for adults.
Best Food Sources of Copper
The following foods have high concentrations of copper, containing at least 50% of the recommended dietary allowance per serving, making them our best food sources of this valuable antioxidant vitamin!
Good Food Sources of Copper
The following foods are also excellent or good sources of copper, containing at least 10% (and up to 50%) of the daily value per serving.
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