Acute Effects. Acute adverse effects of excess zinc have been reported. These include epigastric pain, nausea, vomiting, loss of appetite, abdominal cramps, diarrhea, and headaches (Prasad, 1976; Samman and Roberts, 1987). Fosmire (1990) estimated that an emetic dose of zinc sulfate was approximately 1 to 2 g of the salt (225 to 450 mg of zinc). Gastrointestinal distress has been reported at doses of 50 to 150 mg/day of supplemental zinc (Freeland-Graves et al., 1982).
Immunological Response. Intake of 300 mg/day of supplemental zinc as the sulfate for 6 weeks has been shown to cause some functional impairment in immunological response as well as significantly decreased concentrations of HDL cholesterol (Chandra, 1984).
Lipoprotein and Cholesterol. Two studies (Black et al., 1988; Hooper et al., 1980) have found that zinc at doses between 50 and 160 mg/ day decreased serum lipoprotein and cholesterol concentrations in men. Samman and Roberts (1988), however, reported no depression of HDL concentrations in men at 150 mg/day of zinc and found some indication of a depression of low-density lipoproteins (LDL) in women. The different response to excess zinc in women was supported by an earlier study by Freeland-Graves and coworkers (1982). The reduction in HDL cholesterol concentration was shown to be transient and not dose related.
Reduced Copper Status. Reduced copper status has been associated with increased zinc intake (Boukaiba et al., 1993; Burke et al., 1981; Festa et al., 1985; Fischer et al., 1984; Prasad et al., 1978; Samman and Roberts, 1988; Yadrick et al., 1989) (Table 12-7). In all studies in which the interaction of excess zinc and copper was measured, there was a consistent decrease in erythrocyte copper-zinc superoxide dismutase (ESOD) activity, an erythrocyte enzyme indicative of copper status. Yadrick and coworkers (1989) reported this effect after total zinc intakes of about 60 mg/day (50-mg supplement plus 10 mg of dietary zinc) for up to 10 weeks. Although the clinical significance of the depressed ESOD activity is unknown, this marker enzyme is known to be a sensitive indicator of the effect of high zinc levels on copper homeostasis.
Zinc-Iron Interactions. Zinc and iron are known to interact, and Whittaker (1998) has reviewed the available studies (also see “Factors Affecting the Zinc Requirement”).