Studies of marginal zinc deprivation in rhesus monkeys. III. Effects on vitamin A metabolism

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Abstract
The relationship between dietary zinc, vitamin A, and retinol-binding protein (RBP) was studied in pregnant rhesus monkeys. Beginning on day 0 of gestation, monkeys were divided into three groups; 1) eight ad libitum-fed controls (AL) fed a diet containing 100 µg/g zinc, 2) 15 zinc-deprived (ZD) fed a diet containing 4 & #x00B5;g/g zinc, 3) 11 pair-fed controls (PF) fed the 100 µg/g control diet in amounts equal to those consumed by ZD animals. ZD monkeys had lower plasma zinc levels than did the AL and PF groups at day 135 of gestation, and at 1 and 3 months gestation. A positive correlation between plasma vitamin A and plasma zinc was observed (r = 0.5150, p < 0.05) and between RBP and zinc (r = 0.883, p < 0.001) in the ZD group at day 135 of pregnancy. By 3 months postpartum, plasma zinc levels increased in all groups; a positive correlation between zinc and vitamin A was observed in the ZD group (r = 0.5162, p < 0.05) and in the PF group (r = 0.6353, p < 0.05); however, no correlation between zinc and RBP was observed. In ZD monkeys, the ratio of RBP to vitamin A was higher (p < 0.05) than in controls at day 135 of pregnancy. Polynomial regression of the interaction between plasma vitamin A and zinc, and the RBP/vitamin A and zinc, indicated a curvilinear relationship between plasma zinc and these two parameters. These results suggest that there is an interrelationship among zinc, vitamin A, and RBP, and indicate that marginal zinc status may alter vitamin A metabolism, with potentially important implications for pregnant women whose dietary intakes may be less than adequate.