complex (1,000 mg/day of calcium) having no statistically significant effect on zinc absorption (McKenna et al., 1997). Differences could be related to the calcium sources, techniques used, and the extent of luminal zinc solubility. At present, data suggest consumption of a calcium-rich diet does not have a major effect on zinc absorption at an adequate intake level of the nutrient. Calcium effects at low dietary zinc intakes have not been adequately investigated. Dietary phosphorus-containing salts over an extensive intake range have not been shown to influence zinc balance (Greger and Snedeker, 1980; Spencer et al., 1984). Other dietary sources of phosphorus include phytate and phosphorus-rich proteins, for example, milk casein and nucleic acids, all of which bind zinc tenaciously and decrease zinc absorption.
Large-scale studies on the influence of dietary copper intake on zinc absorption and utilization have not been carried out with human subjects. Various experimental approaches with animals have not revealed a uniform influence of copper on intestinal zinc uptake (Cousins, 1985; Sandstrom and Lonnerdal, 1989). Rather, evidence for an interaction derives from the therapeutic effect of zinc in reducing copper absorption in patients with Wilson’s disease (Yuzbasiyan-Gurkan et al., 1992). This action includes the induction of intestinal metallothionein by zinc and the subsequent binding of excess copper by this metalloprotein, which may limit transcellular copper absorption. The relationship may have relevance in situations where zinc supplements are consumed with marginal dietary copper intake.
Folate bioavailability is enhanced when polyglutamate folate is hydrolyzed by the zinc-dependent enzyme, polyglutamate hydrolase, to the monoglutamate. This occurrence suggests a possible point of interaction. Some studies have shown a relationship between folate and zinc (Milne et al., 1984), with low zinc intake decreasing folate absorption/status. More recent evidence does not support any effect of low zinc intake on folate utilization and shows that folate supplementation does not adversely affect zinc status (Kauwell et al., 1995). Extensive studies on this potential relationship have not been carried out in women. Given that these nutrients have important functions in both fetal and postnatal development, the relationship requires further study.