Effect of Calcium, Phosphorus and Zinc on Zinc-65 Absorption and Turnover in Rats Fed Semipurified Diets

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Abstract
The objectives of this study were to assess the effects of dietary levels of calcium, phosphorus and zinc on zinc absorption and turnover in rats fed semipurified diets. In 7 experiments 65Zn-glycine was administered by diet, gavage and intramuscular injection to growing rats fed the various diets and 65Zn absorption and turnover were assessed by techniques described previously. Calcium decreased (P < 0.01) absorption of 65Zn in the presence of approximately 1% dietary inorganic phosphorus but not when phosphorus was 0.3 to 0.5%. Intermediate levels of phosphorus gave variable results. Calcium decreased (P < 0.05) the biological half-life of oral 65Zn zero to 44 hours post-administration and increased (P < 0.01) it 100 to 300 hours post-administration, both effects being independent of dietary phosphorus. Calcium decreased (P < 0.01) the proportion of the body 65Zn in liver and kidneys at 345 hours post-administration, and increased (P < 0.05) the proportion in bone. When the diet contained sufficient inorganic phosphorus, the effects of calcium on 65Zn metabolism with a semipurified diet containing protein of animal origin and no phytic acid were analogous to those observed earlier in rats fed a practical diet containing plant protein. Omitting zinc from a diet containing casein hydrolysate permitted almost complete absorption of dietary 65Zn and markedly increased body retention of 65Zn. Zinc deficiency caused a greater proportion of the body 65Zn to be in the liver at 385 hours post-administration and a smaller proportion to be in bone.