Copper Digestion and Absorption
The absorption of copper takes place mainly from the small intestine and to a lesser extent from the stomach. Prior to the absorption of copper in the cuprous (Cu+) state being able to take place from the small intestine, the copper needs to be reduced from the cupric (Cu++) state. This is accomplished to some extent by the acidic environment of the stomach, but primarily by the action of reductases on cell membranes.
The body more easily absorbs copper than many other minerals. The gastrointestinal tract typically absorbs approximately 50% to 80% of all the copper ingested. A compensatory mechanism is in place, just as there is for iron, whereby copper absorption percentage adjusts upward or downward based on how badly the body needs more of it. Absorption efficiency increases when copper intake is less and decreases, when copper intake is greater. For example, with a low copper intake (below 1 mg./day) copper absorption is likely to increase to above 50%, while with a high copper intake (over 5 mg./day), the absorption rate may drop to as low as 20%.
Meanwhile, copper absorption efficiency can be either enhanced or inhibited by a whole host of other factors. Except in the case of malabsorption caused by an underlying disease, these variables are largely controllable by the individual.
Enhancers of copper absorption
The presence of any of the following can facilitate the absorption of copper.
• Amino acids, such as histidine and cysterine , which bind to copper
• Organic acids in foods, such as citric, gluconic, lactic, acetic, and malic acids that act as binding ligands to make copper more soluble and, therefore, more absorbable
Inhibitors of copper absorption
Conversely, the presence of any of the following can make the absorption of copper more difficult.
• Excessive antacid intake or proton pump inhibitors, or common OTC medications like Zantac (ranitidine), Tagamet (cimetidine), or Pepcid (famotidine).
The problem is that while an acidic environment makes copper easier to absorb, an alkaline environment does the opposite. There, the copper tends to bind to hydroxides to form insoluble compounds that are not readily absorbed.
• Phytic acid (found in cereal and legumes)
Zinc supplements in the amount of 40 mg. or more per day can interfere with the absorption of copper. Copper deficiency resulting from high dosages of zinc supplements has been found to be difficult to correct, even when the zinc is discontinued, and copper supplements are given instead.
Molybdenum is another nutrient that interacts incompatibly with copper. Increased molybdenum intake causes more copper to be excreted in the urine.
• Vitamin C
• Iron in large quantities
Copper and iron compete for the same transport proteins in the enterocyte membranes. Therefore, a large iron intake can cause decreased absorption of copper.
• Any underlying medical disorder causing impaired absorption
Copper absorption is a fairly rapid process, taking no more than 15 minutes. Absorbed copper (usually bound to amino acids, glutathione, or other proteins), can either be stored in or used by enterocytes or transported by the blood to be used by other tissues.
Most of the copper circulating in the blood is found in ceruloplasmin, which then binds to cell membrane receptors, where reductases reduce the Cu++ to Cu + so that uptake of the copper into the cells can proceed.
The liver is the primary site for storing copper. Copper inside the cells is bound to the protein metallothinein.
The primary mode (95%+) of excretion for healthy individuals is through bile into the feces. In individuals with normal hepatic functioning, the liver helps to maintain homeostasis by regulating the amount of copper that is passed in the feces in direct proportion to dietary intake. If the dietary intake of copper is high, larger amounts will be excreted in the feces than if the dietary intake of copper is low. In Wilson’s disease, discussed earlier, this function of the liver is disturbed, and toxic amounts of copper remain in the body. Small amounts of copper are also excreted via urine, sweat, the skin, hair, and nails, and menses and semen.