Zinc Retention Research Articles

The influence of pH and chloride on the retention of cadmium, lead, mercury, and zinc by soils

Abstract The extent of contamination of soils by toxic heavy metals not only depends on the rate of loading of the metal but also on the nature of the adsorbing surfaces, the degree of alkalinity or acidity of the soil and the presence of aqueous complexant ligands. This work reports on the role of pH on the retention of Cd, Hg, Pb and Zn by two soils and on the influence of the chloride, Cl‐, ion on the chemical speciation and retention of the four metals. Batch adsorption experiments were conducted from pH 3 to 7 in the presence of either 0.1 M LiCl or LiClO4. The results of the study showed that high concentrations of Cl‐ ions can greatly decrease the retention of Hg and have an increasingly lesser effect on Cd, Pb and Zn retention. The effect of the Cl‐ons was directly related to the metal‐Cl formation constants. The results of computer modeling of Cd and Hg retention by goethite and humic acid fractions indicated the relative importance of aqueous vs. surface complexation on metal retention. For orga...

Zinc Source Influences Zinc Retention in Hair and Hair Growth in the Dog

Zinc absorption has been shown to vary as a func tion of the source of the zinc in the diet (Ho and Hdiroglou 1977, Ashmead et al. 1985, Wedekind and Baker 1990, Wedekind et al. 1990) and, in dogs, as a function of the presence or absence of dietary antag onists (Robertson and Burns 1963). Zinc absorption also varies as a function of the ac tual quantity of zinc in the diet (Mejborn 1990), the effect being with respect to the absolute amount of zinc absorbed with increasing dietary zinc, in contrast to the percentage absorption that may remain un changed. Problems may, however, arise as a result of increas ing the zinc content of a diet in an attempt to increase zinc absorption form the gut. The increase in zinc content of the diet may result in interaction with an other mineral causing a reduction in absorption of that mineral. Increasing dietary zinc above the minimum recommended, however, remains common practice to counteract antagonist effects on zinc absorption (NRC 1985) in many commercial diets. It has been suggested that when dietary zinc is sup plied in the form of a chelate with amino acids, rather than from inorganic sources, a greater proportion of zinc is absorbed. Depending on the amino acids used to chelate the zinc, the retention of zinc in tissues may be increased (Ashmead et al. 1989) and the undesirable effects that dietary antagonists exert on zinc absorp tion may be negated. Thus the inclusion of a zinc chelate in a diet for dogs may allow for the improvement of zinc absorp tion irrespective of the presence of dietary antagonists without the need to increase the total zinc supply in the diet. The purpose of this study was to compare two sources of zinc, zinc-amino acid chelate (2 mol metgly:l mol Zn) containing 20% Zn (ZM) and a zincpolysaccharide complex consisting of zinc sulphate complexed with alkali-modified brewers wort (the liq uid portion of malted grain), 16.7% Zn (ZP) as a re placement for Zn from zinc oxide when added to a commercial diet formulation. Materials and methods. Each zinc source was added to a typical commercial diet formulation (Table 1) that contained no added zinc. An equivalent of an additional 50 mg Zn • kg'1 as either ZO, ZM or ZP was

Absorption and Retention of Zinc when Administered as an Amino-Acid Chelate in the Dog

Absorption and Retention of Zinc when Administered as an Amino-Acid Chelate in the Dog

Parenteral nutrient needs of very low birth weight infants

Objective: To determine nitrogen and mineral needs in parenterally nourished very low birth weight infants. Design: Prospective observational study. Setting: Neonatal intensive care unit. Patients: Twenty-four very low birth weight infants (<1.2 kg) expected to receive parenteral nutrition (PN) exclusively for 3 weeks beginning 3 days after birth. Interventions: Infants received PN solutions according to nursery protocol. Serial 24-hour balance studies were conducted twice weekly. Clinical therapies were tabulated. Main outcome measures: Intake, urinary excretion, and apparent retention of nitrogen, sodium, potassium, zinc, copper, calcium, phosphorus, and magnesium after initiation of PN. Results: Although urinary K, Zn, Ca, P, and Mg excretion (but not N, Na, and Cu excretion) increased after PN therapy was begun, net nutrient retention increased significantly above baseline for all nutrients. Average weekly nutrient retention was significantly below intrauterine estimates of nutrient accretion for N, Na, Ca, P, and Cu; closely approximated estimates for Zn; and significantly exceeded those for K and Mg. Regression analysis was used to predict parenteral nutrient intakes that would support postnatal nutrient retentions equivalent to the intrauterine estimates. Postnatal therapy with dexamethasone affected N, P, and K excretion and retention. Conclusions: Soon after PN administration is begun, positive nutrient balance may be achieved early in the neonatal period. The magnitude of this effect remains uniform during PN administration. Adjustments in parenteral nutrient intake are needed to provide nutrient intakes sufficient to support postnatal retention at rates similar to those of intrauterine accretion. These data should be considered in the design of future studies to determine optimal PN needs of very low birth weight infants. (J P EDIATR 1994;125:961-8)

Immobilized Cyanobacteria for Online Trace Metal Enrichment by Flow Injection Atomic Absorption Spectrometry

Cyanobacteria (Spirulina platensis) immobilized on controUed pore glass preconcentrate Cu(II), Zn(II), Cd(II), Pb(II), and Fe(III) from aqueous solution with high efficiency as ascertained using an on-line flow injection atomic absorption spectrometry system. The degree of metal binding depends on the pH of the solution. Quantitative retention of copper, zinc, and cadmium occurred at a wide range of pH values, while the retention for lead and iron was pH-dependent. The latter metals were adsorbed strongly only at pH 6 and 7, respectively. The breakthrough capacity was determined from the breakthrough curve, with values of 0.00035, 0.0008, 0.0011, 0.0028, and 0.0017 ng/mL for Cu, Zn, Cd, Pb, and Fe, respectively, being obtained

Effect of oral and i.v. iron on tissue retention and excretion of copper and zinc in growing rats

ZusammenfassungWirkung von oralem und i.v. Eisen auf die Gewebsretention und die Ausscheidung von Kupfer und Zink bei wachsenden RattenDer Einfluß von oral und intravenös verabreichten Eisenzulagen auf den Kupfer‐ und den Zinkstoffwechsel wurde in einem 20tägigen 3 × 2faktoriellen Versuch mit 30 wachsenden Sprague‐Dawley Ratten untersucht. Eine halbsynthetische Ration mit einem Eisengehalt von ca. 4 ppm wurde nicht oder mit 40 ppm bzw. 400 ppm organischem, dreiwertigem Eisen supplementiert. Die Hälfte der Tiere jeder oralen Behandlungsgruppe erhielt zu Beginn des Versuchs eine einmalige Dosis von 2,72 mg Fe in die Schwanzvene. Alle Diäten wurden mit anorganischem Kupfer (12 ppm) und Zink (50 ppm) supplementiert. Aufnahme sowie Kot‐ und Harnausscheidung an Kupfer und Zink wurden von Tag 7 bis Tag 20 des Versuchs vollständig erfaßkt. Eine Reihe von Organen und Geweben wie auch die Restkörper wurden auf die Gehalte an Cu und Zn untersucht.Eine steigende Eisenaufnahme zeigte keine systematischen Wirkungen auf die Kupferbilanz. Auch die Ganzkörpergehalte an Kupfer unterschieden sich nicht zwischen den oralen Behandlungen und machten im Durchschnitt 0,21 mg aus. In Leber, Nieren, Dünndarm und Blut trat ein Rückgang in Kupfergehalt und ‐bestand mit steigender Eisenzufuhr auf. Das intravenös verabreichte Eisen hatte keinen signifikanten Einfluß auf den Kupferstoffwechsel mit Ausnahme des Schwanzgewebes als der Injektionsstelle. Die Zinkabsorption wurde durch die steigende Eisenaufnahme beeinträchtigt. Insgesamt ging die Absorptionsrate beim Zink von 41% über 35% auf 29% mit 0 ppm, 40 ppm und 400 ppm supplementiertem Eisen zurück. Auch in einigen Organen und Geweben wie Dünndarm, Leber und Femora wurden die Zinkgehalte durch oral zugeführtes Eisen verringert. Die Unterschiede in den Ganzkörpergehalten fielen geringer aus, wobei im Mittel 4,2 mg Zink gefunden wurden. Wegen des erheblichen Anstiegs im Hämatokrit wurde der Zinkgehalt des Bluts durch steigende orale Eisenzufuhr sogar erhöht. Es traten keine Effekte von parenteralem Eisen auf Zinkretention und ‐ausscheidung auf. Die einzige wesentliche Interaktion zwischen oral und parenteral verabreichtem Eisen ergab sich bei der Zinkkonzentration im Blutkuchen, wobei jegliche Eisensupplementation von einem signifikanten Rückgang begleitet war.

Sodium iron EDTA [NaFe(III)EDTA] as a food fortificant: the effect on the absorption and retention of zinc and calcium in women

The iron fortificant NaFeEDTA could have a potential negative effect on the metabolism of other minerals. We have used stable isotopes to monitor zinc and calcium metabolism in 10 women consuming a single meal of high-extraction wheat rolls (100 g flour) fortified with 5 mg Fe as either FeSO4 or NaFeEDTA. Six-day chemical balances were made simultaneously to study apparent zinc and calcium retention from the complete diet containing the differently iron-fortified breads (200 g flour; 10 mg added Fe/d). Mean 70Zn absorption from the bread meal increased from 20.9% with FeSO4 to 33.5% with NaFeEDTA (P < 0.05) whereas mean 44Ca absorption was 53.3% from both breads. When NaFeEDTA-fortified bread was consumed, there was a small but significant increase in urinary excretion of 70Zn and 44Ca. There was a similar small increase in urinary zinc excretion during the 6-d balance, although the apparent retention of zinc and calcium was not different. Thus, we found no negative overall effect of NaFeEDTA consumption on the metabolism of zinc and calcium. In contrast, the results suggest that NaFeEDTA added to low-bioavailability diets might increase zinc absorption as well as provide iron with high bioavailability.

Effects of 1,25-Dihydroxycholecalciferol and Phytase on Zinc Utilization in Broiler Chicks

Studies were conducted with corn-soybean meal diets to evaluate the effects of phytate phosphorus utilization on zinc absorption and retention in broiler chicks. In the first two experiments, zinc-65 was used to determine zinc absorption. Experiment 1 was a 2 × 2 factorial with 0 or 5 μg/kg dihydroxycholecalciferol and 0 or 40 ppm supplemental zinc. In Experiment 2, 5 μg/kg 1,25-dihydroxycholecalciferol [l,25-(OH)2 D3] or 750 units/kg phytase or both were added to a diet containing 35 ppm zinc. The diets in Experiment 3 were similar to Experiment 2 except that 600 units/kg phytase was fed. Experiment 4 was similar to Experiment 3 except that dietary phosphorus was decreased by .15%. There were no treatment effects on body weight in Experiments 1 and 2. Zinc absorption was higher in zinc-deficient birds in Experiment 1, but there were no other effects on zinc-65 absorption or retention. Body weight was increased by l,25-(OH)2 D3 in Experiments 3 and 4 and by phytase in Experiment 4. Phytate phosphorus retention was increased by phytase and l,25-(OH)2 D3 and was increased additively when both sources were fed. Dietary l,25-(OH)2 D3 increased zinc retention at times during Experiments 3 and 4, but this response was inconsistent. Phytase did not affect zinc retention. Phytase plus l,25-(OH)2 D3 increased zinc retention synergistically in Experiment 3. Bone zinc was increased by l,25-(OH)2 D3 and phytase, and there was an additive effect in Experiment 3. Plasma zinc and alkaline phosphatase were not affected. The results suggest that supplemental zinc may be decreased in a corn-soybean meal diet when phytate phosphorus utilization is enhanced.

Low or high meat consumption: Effects on triglycerides, HDL cholesterol, and indices of iron nutriture in postmenopausal women

The effects of high and low meat diets on biochemical indices of nutritional status were determined as part of a controlled, metabolic unit study of meat consumption and zinc retention. Fourteen postmenopausal women, age (mean ± SD) 62.9 ± 6.1 y (range 51 to 70), with body mass index of 26.9 ± 4.8 kg/m2 (20.6 to 36.8) consumed three weighed, experimental diets—high meat, low meat, or low meat with mineral supplements—for 7 wk each in random order. The additional meat in the high meat diet was provided by 145 g lean beef, 115 g chicken, 160 g lean ham, and 35 g tuna per 2-d menu cycle with 2000 kcal/d, by replacing some fruits, sucrose, and fat principally from corn oil margarine in the low meat diet. The low and high meat diets contained, respectively, 10 and 20% protein, 61 and 52% carbohydrate, 29 and 28% fat (as a proportion of energy), 1.3 and 1.0 ratios of linoleate to total saturated fatty acids, 73 and 189 mg cholesterol/2000 kcal, 168 and 172 mg ascorbic acid/2000 kcal (calculated) and 10 and 12.5 mg iron/2000 kcal (analyzed). As a third experimental diet, the low meat diet was supplemented to be similar to the high meat diet in potassium, phosphorus, iron, magnesium, and zinc content. Serum lipids were determined after 6 and 7 wk, and indices of iron nutriture after 7 wk on each diet. The high meat diet, compared to the low meat or low meat supplemented diets, was associated with higher HDL cholesterol (1.50 vs 1.36 or 1.39 mmol/L, p<0.0005) and lower triglycerides (1.39 vs 1.66 or 1.72 mmol/L, p<0.0003), without change in total or LDL cholesterol. The high meat diet, compared to the low meat or low meat supplemented diets, was also associated with lower serum ferritin (74 vs 82 or 82 μg/L, p<0.02), higher total iron binding capacity (57.8 vs 52.8 or 53.0 μmol/L, p<0.002) and lower transferrin saturation (27.2 vs 31.4 or 30.9%, p<0.03), with no change in hematocrit, hemoglobin, erythrocyte zinc protoporphyrin, serum transferrin, or serum iron. These results suggest that substituting lean meat for carbohydrate and vegetable fat increases HDL cholesterol despite modest increases in dietary cholesterol and saturated fat. The negative effect of meat consumption on indices of iron status was unexpected, and is in contrast with previous studies of enhanced bioavailability of iron from meat. The results emphasize the need for testing effects of nutritional variables in the context of a whole diet of conventional foods, and for identifying additional dietary components that influence lipid metabolism and iron nutriture.

Zinc and iron utilization in young women consuming a beef-based diet

The purpose of this study was to determine the utilization of zinc in young adult women fed diets containing varying amounts of lean ground beef. A secondary objective was to determine the utilization of iron. The 28-day study was divided into one 7-day preexperimental period, during which a vegetarian diet was fed, and three randomly arranged 7-day experimental periods. During the experimental periods, the diets contained 3, 6, or 9 oz of beef, supplying varying levels of zinc and iron. Complete collections of urine and fecal samples were obtained from each subject. All the diets resulted in positive zinc balance; however, mean zinc balances were significantly higher when subjects consumed the experimental diets containing beef. When data for all diets containing beef were combined, mean values for apparent zinc absorption and zinc retention were not significantly higher than values that resulted from the vegetarian diet. Consumption of all diets resulted in a positive iron balance; however, mean iron balances were significantly higher for diets containing beef. As the amount of beef in the diet increased, the bioavailability of iron increased. We found that zinc and iron utilization was enhanced after consumption of a diet including lean ground beef. Results of this study also suggest that little increase in zinc and iron utilization is realized by including more than 3 oz beef per day in the diet.

Zinc retention from an experimental diet based on the U.S.F.D.A. total diet study

To investigate retention of Zn from U.S. diets, two research diets were developed using 200 foods which represent average intakes of 25–30 year-old U.S. men and women, respectively (FDA Total Diet Study). The women's diet contained 7.8 mg Zn (analyzed) and 1570 kcal (calculated) daily; the men's diet contained 14.0 mg Zn and 2545 kcal. The diets were consumed by 14 women and 14 men for nine weeks. Although the food lists were intended to represent typical intakes in the U.S., they did not provide sufficient energy for weight maintenance. Despite energy adjustments with sucrose, followed by a 10% increase in all foods, the women lost (mean±SD) 4.4±1.4 and the men, 4.0±1.7 kg. The entire 3-d menu was extrinsically labelled with Zn-65 during week 3. Zn retention was monitored by whole body scintillation counting. Oral contraceptives did not affect Zn retention. Women absorbed a larger proportion of Zn from their diet (29±8 vs 22±4%), but less total Zn (2.3±0.6 vs 3.1 ±0.5 mg), and retained the Zn with a shorter biological half-life (147±32 vs 182±32 d) than men. Men and women absorbed similar amounts of Zn per kg. Although the difference in body weight between men and women was less than the difference in dietary Zn, the women apparently compensated by absorbing Zn more efficiently. Approximately a quarter of the Zn in a representative U.S. diet was absorbed.

Zinc toxicity in ectomycorrhizal Pinus sylvestris

Six strains of ectomycorrhizal fungi were compared for their ability to increase zinc tolerance in Pinus sylvestris L. seedlings. Pioneer and ‘late-stage’ fungi as well as one strain collected from a Zn-polluted site were included in the study. The accumulation of zinc in the host plants was determined at two different sublethal substrate Zn concentrations. The mycobionts varied considerably in their protection of the autobionts against zinc toxicity. Several fungal species reduced zinc accumulation in the pine seedlings. A Thelephora terrestris (Ehrh.) Fr. Strain, however, increased the Zn concentration in its host plants. Specific zinc-retaining capacity of the mycelium and density of the extramatrical mycelium were important features determining the effectiveness of the zinc retention in the fungal symbiont.

Calcium and zinc retention from protein hydrolysate formulas in suckling rhesus monkeys.

To determine calcium and zinc retention from infant formulas based on protein hydrolysates. Randomized, crossover. Newborn nursery at the California Primate Research Center, Davis. Suckling infant rhesus monkeys (N = 7), aged 6 weeks at the beginning of the study. Each infant received seven different formulas. Fasted infant monkeys were fed diets radiolabeled with calcium 47 and zinc 65. Retention was determined by counting whole body radioactivity immediately after dosing and 7 days after dosing. Retention of 47Ca was a mean (+/- SEM) of 79% +/- 4% from casein hydrolysate and 72% +/- 6% from the whey protein hydrolysate formula. Calcium 47 retention from hydrolysates based on whey protein/casein mixtures (a ratio of 60:40 or 50:50) was similar despite differences in protein sources and calcium content. Calcium 47 retention from two types of soy/collagen hydrolysate formula was found to be 68% +/- 6% and 59% +/- 4%, respectively, which is significantly lower than retention from casein hydrolysate. Considering the different calcium content of these formulas, total calcium retention from milk protein hydrolysates was higher than from soy/collagen products. Retention of 65Zn from milk protein hydrolysates ranged from 18% +/- 3% to 29% +/- 4% and was higher than that from soy/collagen formulas with a mean retention of 7% +/- 3% and 10% +/- 4%, respectively. Despite these differences in 65Zn retention, total zinc retention from all soy/collagen formulas was similar due to their higher zinc content. Calcium and zinc bioavailability was high from formulas based on milk protein hydrolysate, but was considerably lower from soy hydrolysates. Higher levels of calcium and zinc provided in soy hydrolysate formula compensated for the lower bioavailability and resulted in similar amounts of calcium and zinc retained.

Zinc in Surgery

Zinc is an essential trace element which is the cofactor of at least 200 different enzymes. These enzymes play an important role in biochemical processes such as DNA and RNA replication, cell division and protein synthesis. These actions explain the impact of zinc on wound healing and immunity, two important factors that influence the clinical outcome of surgical patients. Early papers as well as more recent ones confirm the effectiveness of zinc supplementation in correcting serum zinc drop and in facilitating wound healing. Zinc status should therefore be corrected before the intervention in the case of marginal deficiency. in the case of major surgev, the stress caused by the intervention provokes a serum zinc drop that can reach 47% of the pre-operative value; this drop exclusively affects the evailable part of serum zinc, thus resulting in an actual decrease of 60% of this index, and can last eight days. the mechanism of this drop, rather than increased output, is explained by retention of zinc by the liver which synthesizes more metallothioneins as a response to the secretion of interleukin I. At least in the case of major surgical interventions, the evidence pleads in favour of daily zinc supplementation started before the intervention in order to restore zinc supplies to peripheral tissues which need more zinc in the days following surgery.

Milk consumption and zinc retention in postmenopausal women : J. Nutr. 1990 120/4 (398–403)

We measured intestinal 65Zn absorption and whole-body retention in postmenopausal women following a meal extrinsically labeled with 65Zn. The meal was consumed with 200 mL of milk or with a calcium phosphate supplement. Fifteen elderly (mean age 69) subjects were studied during three 12-d experimental periods in which they were fed either a basal diet containing 16 mg Zn or the basal diet supplemented either with 400 mL of milk or with dibasic calcium phosphate supplements containing an equivalent amount of calcium (468 mg) and phosphorus (360 mg). Measurements of fractional zinc absorption were made in 9 of the 15 subjects by a dual-isotope technique using 65Zn and 51Cr (as nonabsorbable fecal markers). Fractional zinc absorption was 0.22 +/- 0.06 (mean +/- SEM) after the standard meal, 0.23 +/- 0.06 with added milk and 0.22 +/- 0.03% with the added calcium phosphate supplement. The corresponding values for 65Zn retention in 15 subjects 12 d after dosing were 0.10 +/- 0.01% for all treatments. No significant effect of milk or calcium phosphate supplementation was observed on either 65Zn absorption or retention. We conclude that increased milk consumption with meals has no detrimental consequences on zinc nutriture in elderly women.

Effect of Marginal Maternal Zinc Intake on Zinc Absorption and Growth of 3-September-Old Infant Rhesus Monkeys

One compensatory mechanism for marginal zinc intake may be through an enhanced absorption of zinc. Such a compensatory mechanism could be of value to the neonate, as poor zinc nutriture during early life has severe consequences on growth and development. We studied the uptake of zinc by 3-month-old infant rhesus monkeys born to dams fed control diets (100 micrograms of zinc per gram of diet or zinc-restricted diets (4 micrograms of zinc per gram of diet). Zinc uptake/retention was studied by feeding 3-month-old infant monkeys that had fasted an infant formula containing zinc 65 by gavage. Whole body radioactivity was counted immediately after intubation and on days 10 and 17 after intubation. Regardless of dietary group, 65 zinc retention was high, ranging from 33% to 71% of the dose fed to the monkeys. There were no significant differences between the two dietary groups in the percentage of zinc retention at days 10 and 17. Independent of the dietary group, there was no correlation between plasma zinc and zinc absorption. A positive correlation was found between weight gain and zinc retention in the marginal zinc infants, while a negative correlation between weight gain and zinc retention was observed in the control infants. These observations suggest that the mechanisms underlying growth may be different in infants born to dams fed control vs marginal zinc diets.

Meal protein and zinc levels interact to influence zinc retention by the rat

The relationship between the effect of egg white protein and zinc in a meal on zinc retention was examined by feeding test meals labeled with Zn-65 to rats and monitoring retention of radioactivity with a whole body counter. Corrected retention (an estimate of absorption) was determined by extrapolating to zero time the semilogarithmic plot of Zn-65 retention between 5 and 26 days after the meal. Test meals contained fixed amounts of sucrose, cornstarch, corn oil, and variable amounts of egg white and zinc chloride. Fractional zinc retention was reduced by increasing the usual dietary zinc intake or zinc in the meal, and was enhanced by increasing protein in the meal. Meal zinc and protein interacted, such that with more zinc in the meal, more protein was needed to observe enhanced zinc retention. Enhancement of zinc retention by protein was not linear with the amount of protein and was not related to the protein to zinc ratio in the meal. The interaction was similar whether rats were accustomed to diets containing 14 or 37 mg zinc/kg. These data indicate that zinc absorption is affected by an interaction between the protein and zinc content of a meal, and the dose-response relationship between the amount of zinc consumed and the amount retained may be amplified by a moderate amount of protein.

Oral copper supplementation: effect on copper and zinc balance during acute gastroenteritis in infants

To evaluate the effect of copper supplementation during recovery from acute diarrhea, we randomly assigned 14 hospitalized infants to receive either 80 micrograms copper sulfate.kg body wt-1.d-1 or a placebo. Metabolic balance and plasma copper and zinc concentrations were measured before randomization (period 1) and 6 d after admission (period 2). Fifteen control subjects were studied after respiratory illness. Fecal copper was not affected by supplementation; fecal zinc during period 2 rose significantly only in the copper-supplemented group. Copper retention was significantly higher in the supplemented infants; plasma concentrations increased for period 2 but were similar to those in the placebo group. Zinc concentrations improved over time in both groups but zinc retention was higher in the placebo group for period 2. A significant interference by copper supplementation on zinc absorption was noted. Copper supplementation during the early phase of recovery from diarrhea is not recommended.

Milk Consumption and Zinc Retention in Postmenopausal Women

We measured intestinal 65Zn absorption and whole-body retention in postmenopausal women following a meal extrinsically labeled with 65Zn. The meal was consumed with 200 mL of milk or with a calcium phosphate supplement. Fifteen elderly (mean age 69) subjects were studied during three 12-d experimental periods in which they were fed either a basal diet containing 16 mg Zn or the basal diet supplemented either with 400 mL of milk or with dibasic calcium phosphate supplements containing an equivalent amount of calcium (468 mg) and phosphorus (360 mg). Measurements of fractional zinc absorption were made in 9 of the 15 subjects by a dual-isotope technique using 65Zn and 51Cr (as nonabsorbable fecal markers). Fractional zinc absorption was 0.22 +/- 0.06 (mean +/- SEM) after the standard meal, 0.23 +/- 0.06 with added milk and 0.22 +/- 0.03% with the added calcium phosphate supplement. The corresponding values for 65Zn retention in 15 subjects 12 d after dosing were 0.10 +/- 0.01% for all treatments. No significant effect of milk or calcium phosphate supplementation was observed on either 65Zn absorption or retention. We conclude that increased milk consumption with meals has no detrimental consequences on zinc nutriture in elderly women.

Effect of oral cadmium exposure during pregnancy on maternal and fetal zinc metabolism in the rat

To study the effect of cadmium exposure on maternal and fetal zinc metabolism, rats were exposed to 0, 5, 50, or 100 ppm Cd in the drinking water on Days 6 through 20 of pregnancy. In comparison to controls, fetal and maternal weights were slightly reduced in the 50- and 100-ppm groups, but not the 5-ppm group. Multiple regression analysis revealed that in the 50-ppm group, but not in the 100-ppm group, the decrease in fetal weight was not solely a consequence of decreased maternal weight. Cd accumulated in a dose-dependent manner in both maternal organs and fetuses, although the absolute concentrations in fetuses were very low as compared to those of maternal tissues. In the 50- and 100-ppm groups, zinc concentrations were significantly increased in maternal liver and kidney, and significantly decreased in fetal liver. The changes in tissue Zn concentrations were accompanied by altered Zn-metalloenzyme activities in both maternal and fetal tissues. These findings support the hypothesis that Cd-induced maternal zinc retention is responsible for fetal Zn deprivation and impaired fetal growth.