Dietary Zinc Absorption Research Articles

Absorption of dietary zinc in man: comparison of intrinsic and extrinsic labels using a triple stable isotope method

Determination of true absorption of dietary minerals in human subjects using "extrinsic-tag" approach with stable isotopes requires establishment of its validity. The present study was conducted to test with quantitative aspects absorption of an extrinsic-tag of zinc labeled with 70Zn as compared with an "intrinsic-tag" of the mineral as 68Zn-labeled chicken meat given simultaneously to health male subjects. Three diet periods were used in which diet modulation with respect to zinc dialy intake and nature of protein source (chicken/soy protein isolate) was also examined. Absorption was measured via quantitative fecal isotope balance of 64Zn, 68Zn, 70Zn. For the three diet period 1 (protein: chicken; Zn intake: ZN intake: 10 to 11 mg/day), 2 (protein: chicken/soy protein isolate, 50/50; Zn intake: 10 to 11 mg/day), and 3 (protein: chicken; Zn intake: 7 mg/day), fractional absorption of the extrinsic tag (mean +/- 1 SEM) was 0.46 +/- 0.06, 0.46 +/- 0.06, and 0.66 +/- 0.04 respectively. The comparable values for intrinsic 68Zn were 0.57 +/- 0.06, 0.57 +/- 0.06, and 0.72 +/- 0.04. There was a highly significant correlation (r=0.91), between zinc absorption from the two labels. However, absorption of intrinsic 68Zn was significantly higher (p less than 0.02) during all periods than that for the extrinsic 70Zn. A 50% replacement of protein from chicken meat with the soy protein isolate did not later fractional absorption of zinc from either tag. The ratio of fractional absorption of the extrinsic/intrinsic tag (mean +/- 1 SEM) was 0.79 +/- 0.06, 0.79 +/- 0.04, and 0.92 +/- 0.03 for periods 1, 2, 3, respectively.

Factors affecting the bioavailability of zinc

Host factors and dietary factors determine the absorption of zinc by an individual. There is evidence that the entrance of zinc into the body is regulated at the level of the intestinal mucosa by the adequacy of the host's zinc nutriture. Moreover, a variety of gastrointestinal diseases that interfere with the digestion of food, the secretion of zinc-binding ligand, or transmucosal absorption, per se, reduce the efficiency of zinc absorption. Zinc appears to be more available from breast milk than from cow's milk, and, in general, from foods of animal origin than from foods of plant origin. The task of nutrition researchers is to unravel further the mechanisms involved in normal absorption of dietary zinc in human beings and to pursue the identification of foods and to pursue the identification of foods andars to be more available from breast milk than from cow's milk, and, in general, from foods of animal origin than from foods of plant origin. The task of nutrition researchers is to unravel further the mechanisms involved in normal absorption of dietary zinc in human beings and to pursue the identification of foods and chemicals that enhance or inhibit zinc absorption.

Growth stimulating effect of picolinic acid added to rat diets.

Rats fed either a soybean protein-based diet or a casein-based diet supplemented with picolinic acid gained significantly more weight than rats fed unsupplemented diets. The zinc concentration of the kidneys from the rats fed the diets supplemented with picolinic acid was significantly greater than that of the rats fed the unsupplemented diets. Rats fed a pyridoxine-free diet formulated with vitamin-free casein and supplemented with picolinic acid gained significantly more weight than rats fed an unsupplemented pyridoxine-deficient diet. The zinc concentration of the kidneys from the rats fed the pyridoxine-deficient diet supplemented with picolinic acid was significantly greater than that of the rats fed the unsupplemented diet. Dietary zinc absorption and food efficiency were increased when rats were fed supplemental picolinic acid. The results suggest that picolinic acid may increase the bioavailability of dietary zinc and perhaps other divalent cations which results in increased food efficiency.

Change in apparent and true absorption and retention of dietary zinc with age in rats

Two groups of 16 rats each were fed the same diet with 12.9 ppm Zn. Nine days after each animal was injected with(65)Zn for assessing fecal zinc of endogenous origin, zinc intake and excretion were determined for a six-day period at the age of about five (group I) and nine (II) weeks. At mean growth rates of 5.1 and 5.2 g/day, food consumption per gram of gain was 2.01 g in group I vs 2.86 g in II. Overall, zinc retention amounted to 21 vs 25 μg Zn/g of gain. Apparent absorption averaged 92 vs 74% of Zn intake (132 vs 189 μg/day), while true absorption averaged 98 vs 92%. It was concluded that endogenous fecal zinc excretion was limited to the indispensable loss (F em) in group I (7 μg/day), while it exceeded this minimum loss in group II (33 μg/day). True retention, which reflected total zinc utilization (true absorption times metabolic efficiency), was derived from apparent absorption plusF em (11 μg/day for group II according to the greater metabolic body size of the rats). It averaged 98% of Zn intake in group I vs 80% in group II. The mean metabolic efficiency was 100% vs 87%. The conclusion was that these marked differences between age groups in utilizing the dietary zinc reflected the efficient homeostatic adjustments in absorption and endogenous excretion of zinc to the respective zinc supply status.

Formation constants for citrate-, folic acid-, gluconate- and succinate-proton, -manganese(II), and -zinc(II) systems: relevance to absorption of dietary manganese, zinc and iron

Formation constants for citrate-, folic acid-, gluconate- and succinate-proton, -manganese(II), and -zinc(II) systems: relevance to absorption of dietary manganese, zinc and iron

Effect of Vitamin D on 65Zn Absorption, Distribution and Turnover in Rats

Experiments were designed to study the effect of dietary vitamin D on the absorption, distribution and turnover of 65Zn in growing rats. In the first experiment, whole-animal retention of oral 65Zn by rats fed zinc-supplemented, but not zinc-deficient, diets was slightly (0.1 >P > 0.05) increased by continuous supplementation with vitamin D. Retention of injected 65Zn was not similarly enhanced, suggesting a possible effect on 65Zn absorption. In the second experiment 65Zn absorption and turnover were determined by more detailed analysis of whole-animal 65Zn retention patterns, and the distribution of oral and injected 65Zn at 60 hours postadministration was examined. The effect of vitamin D on uptake of oral 65Zn was most pronounced when the vitamin was suddenly added to the diet of previously vitamin D-deficient rats. At 60 hours skeletal, but not soft tissue, uptake of either oral or injected 65Zn was significantly increased by the supplementation of vitamin D to vitamin D-deficient rats. However, skeletal specific activity (% 65Zn per g) was increased by vitamin D only with the orally administered 65Zn. An explanation consistent with all data is that the increased absorption of dietary zinc attributed to vitamin D probably results, not from a direct effect of the vitamin, but from a homeostatic response to the increased need for zinc which accompanies enhanced skeletal growth and calcification.

Zinc Requirement and Balance Studies with the Rat

In a series of growth and balance studies concerned with investigating factors affecting the zinc requirement of the young albino rat, increasing calcium level from 0.8 to 1.6% of the diet was observed to depress weight gain at all levels of zinc fed both in diets containing casein and those containing isolated soybean protein. Apparent absorption of dietary zinc and its urinary excretion were not affected by increased calcium. Zinc requirement was 18 ppm with 7 ppm derived from soy protein and the remainder from ZnCO3; 12 ppm with 7 ppm supplied from casein and 5 from ZnCO3; and 12 ppm with 2 to 4 ppm derived from egg white and the remainder from ZnCO3. Apparent absorption of zinc from casein, ZnCO3 and isolated soybean protein was 84, 51 and 44%, respectively.