intake. In addition, excretion of copper into the gastrointestinal tract regulates copper retention. As more copper is absorbed, turnover is faster and more copper is excreted into the gastrointestinal tract (Turnlund et al., 1998). This excretion is probably the primary point of regulation of total body copper. This efficient homeostatic regulation of absorption and retention helps protect against copper deficiency and toxicity.
Zinc intakes, well in excess of the amount normally found in the diet, can decrease copper absorption in adults (Turnlund, 1999) (see Table 12-7). In one case report, an infant who was given 16 to 24 mg/day of zinc developed copper deficiency (Botash et al., 1992). Very high doses of zinc have been used to treat patients with Wilson’s disease, an inborn error of copper metabolism resulting in copper toxicity (Brewer et al., 1983). This zinc-induced inhibition of copper absorption could be the result of competition for a common, apically oriented transporter or the induction of metallothionein in intestinal cells by zinc. Because this protein has a higher binding affinity for copper than for zinc, copper is retained within enterocytes and its absorption is reduced. This response has been used as a therapy to diminish copper absorption in patients with Wilson’s disease (Yuzbasiyan-Gurkan et al., 1992). The interaction could also be responsible for reducing copper absorption during consumption of zinc supplements. When zinc-to-copper ratios of 2:1, 5:1, and 15:1 were fed to humans, there were limited effects on copper absorption (August et al., 1989).
High iron intakes may interfere with copper absorption in infants. Infants fed a formula containing low concentrations of iron absorbed more copper than infants consuming the same formula with a higher iron concentration (Haschke et al., 1986). Such an interaction has been reported to produce reduced copper status in infants (Lonnerdal and Hernell, 1994; Morais et al., 1994).
Studies in rats demonstrated that diets very high in fructose were associated with increased severity of copper deficiency in rats (Fields et al., 1984), but a similar effect was not observed in pigs