plasma zinc concentrations in men participating in a 5-hour, 70-km cross-country ski race were 19 percent higher immediately postrace compared to prerace values. However, by day 1 postrace, zinc concentrations were back to control levels. The observation that plasma zinc concentrations can increase significantly during strenuous exercise has since been verified by numerous investigators (Dressendorfer et al., 1982; Lukaski et al., 1984; Ohno et al., 1985; Van Rij et al., 1986). The magnitude of the increase in plasma zinc concentration with exercise is such that it cannot be due to hemoconcentration (Hetland et al., 1975; Lukaski et al., 1984); rather it is thought to reflect the result of muscle leakage of zinc into the extracellular fluid following muscle breakdown (Karlson et al., 1968). Following the cessation of exercise, there is normally a rapid drop in plasma zinc levels back to preexercise concentrations within a short period. It is thought that this rapid postexercise drop in plasma zinc is due to a high urinary excretion of the element coupled with a shift in the distribution of the element from the plasma fraction into the liver (Anderson et al., 1984; Campbell and Anderson, 1987; McDonald and Keen, 1988). The shift of zinc from the plasma into the liver is thought to be in part a consequence of the so-called acute-phase response, which occurs as a consequence of stressors such as infection, inflammation, and trauma. These stressors can result in the elaboration of cytokines, which result in the stimulation of the synthesis of several liver proteins (Cannon and Kluger, 1983; Cousins, 1985; Dinarello, 1989; Keen and Hackman, 1986; Singh et al., 1991). With regard to zinc, one component of the acute-phase response is an increase in liver metallothionein concentration, which can result in a sequestering of zinc in the liver (Cousins, 1985; Whanger and Oh, 1978). (Serum ferritin concentrations can increase as a result of the acute-phase response, a fact that must be considered when collecting samples for assessment of iron status; Singh et al., 1991; Taylor et al., 1987.)

Reductions in plasma zinc concentrations were also observed in men who participated in a 5-day intensive training course conducted by the U.S. Navy (Singh et al., 1991). This reduction in plasma zinc occurred despite an increase in dietary zinc intake during the training period. The authors attributed the reduction in plasma zinc primarily to a redistribution of plasma zinc into liver as a consequence of metallothionein synthesis stimulated by interleukin-6 (IL-6). (The observed increase in plasma IL-6 concentrations was associated with tissue trauma.) Consistent with the above finding, Lichton et al. (1988) observed a reduction in plasma zinc concentrations in male soldiers engaged in a 34-day field exercise at an elevation of 1800 m. The field exercise was simulated combat in which the men performed combat-support activities during both day and night and during which time they lost sleep. Activities included digging foxholes, building lava-stone walls, and walking. During the study, subjects were given a military operational